7. Standard Library Functions#
7.1. Basic math functions#
Mathematical constants#
OSL defines several mathematical constants:
Constant 
Value 


\(\pi\) 

\(\pi/2\) 

\(\pi/4\) 

\(2/\pi\) 

\(2\pi\) 

\(4\pi\) 

\(2/\sqrt{\pi}\) 

\(e\) 

\(\ln 2\) 

\(\ln 10\) 

\(\log_2 e\) 

\(\log_{10} e\) 

\(\sqrt{2}\) 

\(\sqrt{1/2}\) 
Mathematical functions#
Most of these functions operate on a generic type that my be any of float
,
color
, point
, vector
, or normal
. For color
and point
like types,
the computations are performed componentbycomponent (separately for x
,
y
, and z
).
type
radians
(type
deg
)
type
degrees
(type
rad
)Convert degrees to radians or radians to degrees.
type
cos
(type
x
)
type
sin
(type
x
)
type
tan
(type
x
)Computes the cosine, sine, or tangent of
x
(measured in radians).void
sincos
(type
x
,output
type
sinval
,output
type
cosval
)Computes both the sine and cosine of \(x\) (measured in radians). If both are needed, this function is less expensive than calling
sin()
andcos()
separately.type
acos
(type
x
)
type
asin
(type
y
)
type
atan
(type
y_over_x
)
type
atan2
(type
y
,type
x
)Compute the principal value of the arc cosine, arc sine, and arc For
acos()
andasin()
, the value of the argument will first be clamped to \([1,1]\) to avoid invalid domain.For
acos()
, the result will always be in the range of \([0, \pi]\), and forasin()
andatan()
, the result will always be in the range of \([\pi/2, \pi/2]\). Foratan2()
, the signs of both arguments are used to determine the quadrant of the return value.type
cosh
(type
x
)
type
sinh
(type
x
)
type
tanh
(type
x
)Computes the hyperbolic cosine, sine, and tangent of \(x\) (measured in radians).
type
pow
(type
x
,type
y
)
type
pow
(type
x, float y
)Computes \(x^y\). This function will return 0 for “undefined” operations, such as
pow(1,0.5)
.type
exp
(type
x
)
type
exp2
(type
x
)
type
expm1
(type
x
)Computes \(e^x\), \(2^x\), and \(e^x1\), respectively. Note that
expm1(x)
is accurate even for very small values of \(x\).type
log
(type
x
)
type
log2
(type
x
)
type
log10
(type
x
)
type
log
(type
x, float b
)Computes the logarithm of \(x\) in base \(e\), 2, 10, or arbitrary base \(b\), respectively.
type
logb
(type
x
)Returns the exponent of x, as a floatingpoint number.
type
sqrt
(type
x
)
type
inversesqrt
(type
x
)Computes \(\sqrt{x}\) and \(1/\sqrt{x}\). Returns 0 if \(x<0\).
type
cbrt
(type
x
)Computes \(\sqrt[3]{x}\). The sign of the return value will match \(x\).
float
hypot
(float x, float y)
float
hypot
(float x, float y, float z)
Computes \(\sqrt{x^2+y^2}\) and \(\sqrt{x^2+y^2+z^z}\), respectively.
type
abs
(type
x
)
type
fabs
(type
x
)Absolute value of \(x\). (The two functions are synonyms.)
type
sign
(type
x
)Returns 1 if \(x>0\), 1 if \(x<0\), 0 if \(x=0\).
type
floor
(type
x
)
type
ceil
(type
x
)
type
round
(type
x
)
type
trunc
(type
x
)Various rounding methods:
floor
returns the largest integer less than or equal to \(x\);ceil
returns the smallest integer greater than or equal to \(x\);round
returns the closest integer to \(x\), in either direction; andtrunc
returns the integral part of \(x\) (equivalent tofloor
if \(x>0\) andceil
if \(x<0\)).type
fmod
(type
a
,type
b
)
type
mod
(type
a
,type
b
)The
fmod()
function returns the floatingpoint remainder of \(a/b\), i.e., is the floatingpoint equivalent of the integer%
operator. It is nearly identical to the C or C++fmod
function, except that in OSL,fmod(a,0)
returns0
, rather thanNaN
. Note that if \(a < 0\), the return value will be negative.The
mod()
function returns \(a  b*\mbox{floor}(a/b)\), which will always be a positive number or zero.As an example,
fmod(0.25,1.0) = 0.25
, butmod(0.25,1.0) = 0.75
. For positivea
they return the same value.For both functions, the
type
may be any offloat
,point
,vector
,normal
, orcolor
.type
min
(type
a
,type
b
)
type
max
(type
a
,type
b
)
type
clamp
(type
x
,type
minval
,type
maxval
)The
min()
andmax()
functions return the minimum or maximum, respectively, of a list of two or more values. Theclamp
function returnsmin(max(x,minval),maxval)
that is, the value \(x\) clamped to the specified range.
type
mix
(type
x
,type
y
,type
alpha
)
type
mix
(type
x
,type
y, float alpha
)The
mix
function returns a linear blending: \( x*(1\alpha) + y*(\alpha) \)type
select
(type
x
,type
y
,type
cond
)
type
select
(type
x
,type
y, float cond
)
type
select
(type
x
,type
y, int cond
)The
select
function returnsx
ifcond
is zero, ory
ifcond
is nonzero. This is roughly equivalent to(cond ? y : x)
, except that ifcond
is a componentbased type (such ascolor
), the selection happens on a componentbycomponent basis. It is presumed that the underlying implementation is not a true conditional and will not incur any branching penalty.int
isnan
(float x)
int
isinf
(float x)
int
isfinite
(float x)
The
isnan()
function returns 1 if \(x\) is a notanumber (NaN) value, 0 otherwise. Theisinf()
function returns 1 if \(x\) is an infinite (Inf
orInf
) value, 0 otherwise. Theisfinite()
function returns 1 if \(x\) is an ordinary number (neither infinite norNaN
), 0 otherwise.float
erf
(float x)
float
erfc
(float x)
The
erf()
function returns the error function \({\mathrm{erf}(x) = \frac{2}{\sqrt{\pi}} \int_0^x e^{t^2}} dt\). Theerfc
returns the complementary error function1erf(x)
(useful in maintaining precision for large values of \(x\)).
7.2. Geometric functions#
ptype
ptype
(float f)
ptype
ptype
(float x, float y, float z)
Constructs a pointlike value (
ptype
may be any ofpoint
,vector
, ornormal
) from individualfloat
values. If constructed from a singlefloat
, the value will be replicated for \(x\), \(y\), and \(z\).ptype
ptype
(string space, f)
ptype
ptype
(string space, float x, float y, float z)
Constructs a pointlike value (
ptype
may be any ofpoint
,vector
, ornormal
) from individualfloat
coordinates, relative to the named coordinate system. In other words,point (space, x, y, z)
is equivalent to
transform (space, "common", point(x,y,z))
(And similarly for
vector
/normal
.)float
dot
(vector A, vector B)
Returns the inner product of the two vectors (or normals), i.e., \(A \cdot B = A_x B_x + A_y B_y + A_z B_z\).
vector
cross
(vector A, vector B)
Returns the cross product of two vectors (or normals), i.e., \(A \times B\).
float
length
(vector V)
float
length
(normal V)
Returns the length of a vector or normal.
float
distance
(point P0, point P1)
Returns the distance between two points.
float
distance
(point P0, point P1, point Q)
Returns the distance from
Q
to the closest point on the line segment joiningP0
andP1
.vector
normalize
(vector V)
normal
normalize
(normal V)
Return a vector in the same direction as \(V\) but with length 1, that is,
V / length(V)
.vector
faceforward
(vector N, vector I, vector Nref)
vector
faceforward
(vector N, vector I)
If
dot (Nref, I)
\(<0\), returnsN
, otherwise returnsN
. For the version with only two arguments,Nref
is implicitlyNg
, the true surface normal. The point of these routines is to return a version ofN
that faces towards the camera — in the direction “opposite” ofI
.To further clarify the situation, here is the implementation of
faceforward
expressed in OSL:vector faceforward (vector N, vector I, vector Nref) { return (I.Nref > 0) ? N : N; } vector faceforward (vector N, vector I) { return faceforward (N, I, Ng); }
vector
reflect
(vector I, vector N)
For incident vector
I
and surface orientationN
, returns the reflection directionR = I  2*(N.I)*N
. Note thatN
must be normalized (unit length) for this formula to work properly.vector
refract
(vector I, vector N, float eta)
For incident vector
I
and surface orientationN
, returns the refraction direction using Snell’s law. Theeta
parameter is the ratio of the index of refraction of the volume containingI
divided by the index of refraction of the volume being entered. The result is not necessarily normalized and a zerolength vector is returned in the case of total internal reflection. For reference, here is the equivalent OSL of the implementation:vector refract (vector I, vector N, float eta) { float IdotN = dot (I, N); float k = 1  eta*eta * (1  IdotN*IdotN); return (k < 0) ? vector(0,0,0) : (eta*I  N * (eta*IdotN + sqrt(k))); }
void
fresnel
(vector I, normal N, float eta, output float Kr, output float Kt, output vector R, output vector T)
According to Snell’s law and the Fresnel equations,
fresnel
computes the reflection and transmission direction vectorsR
andT
, respectively, as well as the scaling factors for reflected and transmitted light,Kr
andKt
. TheI
parameter is the normalized incident ray,N
is the normalized surface normal, andeta
is the ratio of refractive index of the medium containingI
to that on the opposite side of the surface.point
rotate
(point Q, float angle, point P0, point P1)
point
rotate
(point Q, float angle, vector axis)
Returns the point computed by rotating point
Q
byangle
radians about the axis that passes from pointP0
toP1
, or about theaxis
vector centered on the origin.ptype
transform
(string tospace,
ptype
p)
ptype
transform
(string fromspace, string tospace,
ptype
p)
ptype
transform
(matrix Mto,
ptype
p)
Transform a
point
,vector
, ornormal
(depending on the type of the ptype p argument) from the coordinate system named byfromspace
to the one named bytospace
. Iffromspace
is not supplied,p
is assumed to be in “common” space coordinates, so the transformation will be from “common” space totospace
. A \(4 \times 4\) matrix may be passed directly rather than specifying coordinate systems by name.Depending on the type of the passed point
p
, different transformation semantics will be used. Apoint
will transform as a position, avector
as a direction without regard to positioning, and anormal
will transform subtly differently than avector
in order to preserve orthogonality to the surface under nonlinear scaling.Technically, what happens is this: The from and to spaces determine a \(4 \times 4\) matrix. A
point
\((x,y,z)\) will transform the 4vector \((x,y,z,1)\) by the matrix; avector
will transform \((x,y,z,0)\) by the matrix; anormal
will transform \((x,y,z,0)\) by the inverse of the transpose of the matrix.float
transformu
(string tounits, float x)
float
transformu
(string fromunits, string tounits, float x)
Transform a measurement from
fromunits
totounits
. Iffromunits
is not supplied, \(x\) will be assumed to be in “common” space units.For length conversions, unit names may be any of:
"mm"
,"cm"
,"m"
,"km"
,"in"
,"ft"
,"mi"
, or the name of any coordinate system, including"common"
,"world"
,"shader"
, or any other named coordinate system that the renderer knows about.For time conversions, units may be any of:
"s"
,"frames"
, or"common"
(which indicates whatever timing units the renderer is using).It is only valid to convert length units to other length units, or time units to other time units. Attempts to convert length to time or vice versa will result in an error. Don’t even think about trying to convert monetary units to time.
7.3. Color functions#
color
color
(float f)
color
color
(float r, float g, float b)
Constructs a
color
from individualfloat
values. If constructed from a singlefloat
, the value will be replicated forr
, \(g\), and \(b\).color
color
(string colorspace, f)
color
color
(string colorspace, float r, float g, float b)
Constructs an RGB
color
that is equivalent to the individualfloat
values in a named color space. In other words,color (colorspace, r, g, b)
is equivalent to
transformc (colorspace, "rgb", color(r, g, b))
float
luminance
(color rgb)
Returns the linear luminance of the color
rgb
, which is implemented per the ITUR standard as \(0.2126 R + 0.7152 G + 0.0722 B\).color
blackbody
(float temperatureK)
The
blackbody()
function returns the blackbody emission (the incandescent glow of warm bodies) expected from a material of the given temperature in Kelvin, in units of \(W/m^2\). Note thatemission()
has units of radiance, so will require a scaling factor of \(1/\pi\) on surfaces, and \(1/4\pi\) on volumes to convert to \(W/m^2/sr\).color
wavelength_color
(float wavelength_nm)
Returns an RGB color corresponding as closely as possible to the perceived color of a pure spectral color of the given wavelength (in nm).
color
transformc
(string fromspace, string tospace, color Cfrom)
color
transformc
(string tospace, color Cfrom)
Transforms color
Cfrom
from color spacefromspace
to color spacetospace
. Iffromspace
is not supplied, it is assumed to be transforming from “RGB” space.
7.4. Matrix functions#
matrix
matrix
(float m00, float m01, float m02, float m03,
\(~~~~~~~~~~~~~~~~~~~~~~~\)float m10, float m11, float m12, float m13,
\(~~~~~~~~~~~~~~~~~~~~~~~\)float m20, float m21, float m22, float m23,
\(~~~~~~~~~~~~~~~~~~~~~~~\)float m30, float m31, float m32, float m33)
Constructs a
matrix
from 16 individualfloat
values, in rowmajor order.matrix
matrix
(float f)
Constructs a
matrix
withf
in all diagonal components, 0 in all other components. In other words,matrix(1)
is the identity matrix, andmatrix(f)
isf*matrix(1)
.matrix
matrix
(string fromspace, float m00, ..., float m33)
matrix
matrix
(string fromspace, float f)
Constructs a
matrix
relative to the named space, multiplying it by the spacetocommon transformation matrix. If the coordinate system name is unknown, it will be assumed to be the identity matrix.Note that
matrix (space, 1)
returns the spacetocommon transformation matrix. If the coordinate system name is unknown, it will be assumed to be the identity matrix.matrix
matrix
(string fromspace, string tospace)
Constructs a
matrix
that can be used to transform coordinates fromfromspace
totospace
. If either of the coordinate system names are unknown, they will be assumed to be the identity matrix.int
getmatrix
(string fromspace, string tospace, output matrix M)
Sets
M
to thematrix
that transforms coordinates fromfromspace
totospace
. Return 1 upon success, or 0 if either of the coordinate system names are unknown (in which caseM
will not be modified). This is very similar to thematrix(from,to)
constructor, except thatgetmatrix()
allows the shader to gracefully handle unknown coordinate system names.float
determinant
(matrix M)
Computes the determinant of matrix
M
.matrix
transpose
(matrix M)
Computes the transpose of matrix
M
.
7.5. Pattern generation#
float
step
(float edge, float x)
type
step
(type
edge
,type
x
)Returns 0 if \(x < {\mathit edge}\) and 1 if \(x \ge {\mathit edge}\).
The
type
may be any of offloat
,color
,point
,vector
, ornormal
. Forcolor
andpoint
like types, the computations are performed componentbycomponent (separately for \(x\), \(y\), and \(z\)).float
linearstep
(float edge0, float edge1, float x)
type
linearstep
(type
edge0
,type
edge1
,type
x
)Returns 0 if
x
\(\le\)edge0
, and 1 ifx
\(\ge\)edge1
, and performs a linear interpolation between 0 and 1 whenedge0
\(<\)x
\(<\)edge1
. This is equivalent tostep(edge0, x)
whenedge0 == edge1
. Forcolor
andpoint
like types, the computations are performed componentbycomponent (separately for \(x\), \(y\), and \(z\)).float
smoothstep
(float edge0, float edge1, float x)
type
smoothstep
(type
edge0
,type
edge1
,type
x
)Returns 0 if
x
\(\le\)edge0
, and 1 ifx
\(\ge\)edge1
, and performs a smooth Hermite interpolation between 0 and 1 whenedge0
\(<\)x
\(<\)edge1
. This is useful in cases where you would want a thresholding function with a smooth transition.The
type
may be any of offloat
,color
,point
,vector
, ornormal
. Forcolor
andpoint
like types, the computations are performed componentbycomponent.float
smooth_linearstep
(float edge0, float edge1, float x, float eps)
type
smooth_linearstep
(type
edge0
,type
edge1
,type
x
,type
eps)This function is strictly linear between
edge0 + eps
andedge1  eps
but smoothly ramps to 0 betweenedge0  eps
andedge0 + eps
and smoothly ramps to 1 betweenedge1  eps
andedge1 + eps
. It is 0 whenx
\(\le\)edge0eps,
and 1 ifx
\(\ge\)edge1 + eps
, and performs a linear interpolation between 0 and 1 whenedge0
< x <edge1
. Forcolor
andpoint
like types, the computations are performed componentbycomponent.
type
noise
(string noisetype, float u, ...)
type
noise
(string noisetype, float u, float v, ...)
type
noise
(string noisetype, point p, ...)
type
noise
(string noisetype, point p, float t, ...)
Returns a continuous, pseudorandom (but repeatable) scalar field defined on a domain of dimension 1 (
float
), 2 (2float
’s), 3 (point
), or 4 (point
andfloat
), with a return value of either 1D (float
) or 3D (color
,point
,vector
, ornormal
).The
noisename
specifies which of a variety of possible noise functions will be used:"perlin", "snoise"
A signed Perlinlike gradient noise with an output range of \([1,1]\), approximate average value of \(0\), and is exactly \(0\) at integer lattice points. This is equivalent to the
snoise()
function."uperlin", "noise"
An unsigned Perlinlike gradient noise with an output range of \((0,1)\), approximate average value of \(0.5\), and is exactly \(0.5\) at integer lattice points. This is equivalent to the
noise()
function (the one that doesn’t take a name string)."cell"
A discrete function that is constant on \([i,i+1)\) for all integers \(i\) (i.e.,
cellnoise(x) == cellnoise(floor(x))
), but has a different and uncorrelated value at every integer. The range is \([0,1]\), its largescale average is 0.5, and its values are evenly distributed over \([0,1]\)."hash"
A function that returns a different, uncorrelated (but deterministic and repeatable) value at every real input coordinate. The range is \([0,1]\) its largescale average is 0.5, and its values are evenly distributed over \([0,1]\).
"simplex"
A signed simplex noise with an output range of \([1,1]\), approximate average value of \(0\).
"usimplex"
An unsigned simplex noise with an output range of \([0,1]\), approximate average value of \(0.5\).
"gabor"
A bandlimited, filtered, sparse convolution noise based on the Gabor impulse function (see Lagae et al., SIGGRAPH 2012). Our Gabor noise is designed to have somewhat similar frequency content and range as Perlin noise (range \([1,1]\), approximately largescale average of \(0\)). It is significantly more expensive than Perlin noise, but its advantage is that it correctly filters automatically based on the input derivatives. Gabor noise allows several optional parameters to the
noise()
call:"anisotropic",
int
"direction",
vectorIf
anisotropic
is 0 (the default), Gabor noise will be isotropic. Ifanisotropic
is 1, the Gabor noise will be anisotropic with the 3D frequency given by thedirection
vector (which defaults to(1,0,0)
). Ifanisotropic
is 2, a hybrid mode will be used which is anisotropic along thedirection
vector, but radially isotropic perpendicular to that vector. Thedirection
vector is not used ifanisotropic
is 0."bandwidth",
floatControls the bandwidth for Gabor noise. The default is 1.0.
"impulses",
floatControls the number of impulses per cell for Gabor noise. The default is 16.
"do_filter",
intIf
do_filter
is 0, no filtering/antialiasing will be performed. The default is 1 (yes, do filtering). There is probably no good reason to ever turn off the filtering, it is primarily to test that the filtering is working properly.
Note that some of the noise varieties have an output range of \([1,1]\) but others have range \([0,1]\); some may automatically antialias their output (based on the derivatives of the lookup coordinates) and others may not, and various other properties may differ. The user should be aware of which noise varieties are useful in various circumstances.
A particular renderer’s implementation of OSL may supply additional noise varieties not described here.
The
noise()
functions take optional arguments after their coordinates, passed as token/value pairs (similarly to optional texture arguments). Generally, such arguments are specific to the type of noise, and are ignored for noise types that don’t understand them.type
pnoise
(string noisetype, float u, float uperiod)
type
pnoise
(string noisetype, float u, float v, float uperiod, float vperiod)
type
pnoise
(string noisetype, point p, point pperiod)
type
pnoise
(string noisetype, point p, float t, point pperiod, float tperiod)Periodic version of
noise()
, in which the domain wraps with the given period(s). Generally, only integervalued periods are supported.
type
noise
(float u)
type
noise
(float u, float v)
type
noise
(point p)
type
noise
(point p, float t)
type
snoise
(float u)
type
snoise
(float u, float v)
type
snoise
(point p)
type
snoise
(point p, float t)The old
noise(...coords...)
function is equivalent tonoise("uperlin",...coords...)
andsnoise(...coords...)
is equivalent tonoise("perlin",...coords...)
.
type
pnoise
(float u, float uperiod)
type
pnoise
(float u, float v, float uperiod, float vperiod)
type
pnoise
(point p, point pperiod)
type
pnoise
(point p, float t, point pperiod, float tperiod)
type
psnoise
(float u, float uperiod)
type
psnoise
(float u, float v, float uperiod, float vperiod)
type
psnoise
(point p, point pperiod)
type
psnoise
(point p, float t, point pperiod, float tperiod)The old
pnoise(...coords...)
function is equivalent topnoise("uperlin",...coords...)
andpsnoise(...coords...)
is equivalent topnoise("perlin",...coords...)
.
type
cellnoise
(float u)
type
cellnoise
(float u, float v)
type
cellnoise
(point p)
type
cellnoise
(point p, float t)
: The old cellnoise(...coords...)
function is equivalent to
noise("cell",...coords...)
.
type
hashnoise
(float u)
type
hashnoise
(float u, float v)
type
hashnoise
(point p)
type
hashnoise
(point p, float t)
Returns a deterministic, repeatable hash of the 1, 2, 3, or 4D coordinates. The return values will be evenly distributed on \([0,1]\) and be completely repeatable when passed the same coordinates again, yet will be uncorrellated to hashes of any other positions (including nearby points). This is like having a random value indexed spatially, but that will be repeatable from frame to frame of an animation (provided its input is precisely identical).
int
hash
(float u)
int
hash
(float u, float v)
int
hash
(point p)
int
hash
(point p, float t)
int
hash
(int i)
Returns a deterministic, repeatable integer hash of the 1, 2, 3, or 4D coordinates.
type
spline
(string basis, float x,
type
\(\mathtt{y}_0\),type
\(\mathtt{y}_1\), …type
\(\mathtt{y}_{n1}\))
type
spline
(string basis, float x,
type
y[])
type
spline
(string basis, float x, int nknots,
type
y[])
As \(x\) varies from 0 to 1,
spline
returns the value of a cubic interpolation of uniformlyspaced knots \(y_0\)…\(y_{n1}\), or \(y[0]\)…\(y[n1]\) for the array version of the call (where \(n\) is the length of the array), or \(y[0]\)…\(y[nknots1]\) for the version that explicitly specifies the number of knots (which may be less than the full array length). The input value \(x\) will be clamped to lie on \([0,1]\). Thetype
may be any offloat
,color
,point
,vector
, ornormal
; for multicomponent types (e.g.color
), each component will be interpolated separately.The type of interpolation is specified by the
basis
parameter, which may be any of:"catmullrom"
,"bezier"
,"bspline"
,"hermite"
,"linear"
, or"constant"
. Some basis types require particular numbers of knot values – Bezier splines require \(3n+1\) values, Hermite splines require \(2n+2\) values, and all of CatmullRom, linear, and constant requires \(3+n\), where in all cases, \(n \ge 1\) is the number of spline segments.To maintain consistency with the other spline types,
"linear"
splines will ignore the first and last data value; interpolating piecewiselinearly between \(y_1\) and \(y_{n2}\), and"constant"
splines ignore the first and the two last data values.float
splineinverse
(string basis, float v, float y
_{0},... float y
_{n1})
float
splineinverse
(string basis, float v, float y[])
float
splineinverse
(string basis, float v, int nknots, float y[])
Computes the inverse of the
spline()
function, i.e., returns the value \(x\) for whichspline (basis, x, y...)
would return value \(v\). Results are undefined if the knots do not specify a monotonic (only increasing or only decreasing) set of values.
Note that the combination of
spline()
andsplineinverse()
makes it possible to compute a full splinewithnonuniformabscissae:float v = splineinverse (basis, x, nknots, abscissa); result = spline (basis, v, nknots, value);
7.6. Derivatives and area operators#
float
Dx
(float a)
,Dy
(float a)
,Dz
(float a)
vector
Dx
(point a)
,Dy
(point a)
,Dz
(point a)
vector
Dx
(vector a)
,Dy
(vector a)
,Dz
(vector a)
color
Dx
(color a)
,Dy
(color a)
,Dz
(color a)
Compute an approximation to the partial derivatives of \(a\) with respect to each of two principal directions, \(\partial a / \partial x\) and \(\partial a / \partial y\). Depending on the renderer implementation, those directions may be aligned to the image plane, on the surface of the object, or something else.
The
Dz
function is only meaningful for volumetric shading, and is expected to return0
in other contexts. It is also possible that particular OSL implementations may only return “correct”Dz
values for particular inputs (such asP
).float
filterwidth
(float x)
vector
filterwidth
(point x)
vector
filterwidth
(vector x)
Compute differentials of the argument
x
, i.e., the approximate change inx
between adjacent shading samples.float
area
(point p)
Returns the differential area of position
p
corresponding to this shading sample. Ifp
is the actual surface positionP
, thenarea(P)
will return the surface area of the section of the surface that is “covered” by this shading sample.vector
calculatenormal
(point p)
Returns a vector perpendicular to the surface that is defined by point
p
(asp
is computed at all points on the currentlyshading surface), taking into account surface orientation.float
aastep
(float edge, float s)
float
aastep
(float edge, float s, float ds)
float
aastep
(float edge, float s, float dedge, float ds)
Computes an antialiased step function, similar to
step(edge,s)
but filtering the edge to take into account how rapidlys
andedge
are changing over the surface. If the differentialsds
and/ordedge
are not passed explicitly, they will be automatically computed (usingfilterwidth()
).
7.7. Displacement functions#
void
displace
(float amp)
void
displace
(string space, float amp)
void
displace
(vector offset)
Displace the surface in the direction of the shading normal
N
byamp
units as measured in the namedspace
(or “common” space if none is specified). Alternately, the surface may be moved by a fully generaloffset
, which does not need to be in the direction of the surface normal.In either case, this function both displaces the surface and adjusts the shading normal
N
to be the new surface normal of the displaced surface (properly handling both continuously smooth surfaces as well as interpolated normals on faceted geometry, without introducing faceting artifacts).void
bump
(float amp)
void
bump
(string space, float amp)
void
bump
(vector offset)
Adjust the shading normal
N
to be the surface normal as if the surface had been displaced by the given amount (see thedisplace()
function description), but without actually moving the surface positions.
7.8. String functions#
void
printf
(string fmt, ...)
Much as in C,
printf
takes a format stringfmt
and an argument list, and prints the resulting formatted string to the console.Where the
fmt
contains a format string similar toprintf
in the C language. The%d
,%i
,%o
, and%x
arguments expect anint
argument. The%f
,%g
, and%e
expect afloat
,color
, pointlike, ormatrix
argument (for multicomponent types such ascolor
, the format will be applied to each of the components). The%s
expects astring
orclosure
argument.All of the substitution commands follow the usual C/C++ formatting rules, so format commands such as
"%6.2f"
, etc., should work as expected.string
format
(string fmt, ...)
The
format
function works similarly toprintf
, except that instead of printing the results, it returns the formatted text as astring
.void
error
(string fmt, ...)
void
warning
(string fmt, ...)
The
error()
andwarning()
functions work similarly toprintf
, but the results will be printed as a renderer error or warning message, possibly including information about the name of the shader and the object being shaded, and other diagnostic information.void
fprintf
(string filename, string fmt, ...)
The
fprintf()
function works similarly toprintf
, but rather than printing to the default text output stream, the results will be concatenated onto the end of the text file named byfilename
.string
concat
(string s1, ..., string sN)
Concatenates a list of strings, returning the aggregate string.
int
strlen
(string s)
Return the number of characters in string
s
.int
startswith
(string s, string prefix)
Return 1 if string
s
begins with the substringprefix
, otherwise return 0.int
endswith
(string s, string suffix)
Return 1 if string
s
ends with the substringsuffix
, otherwise return 0.int
stoi
(string str)
Convert/decode the initial part of
str
to anint
representation. Base 10 is assumed. The return value will be0
if the string doesn’t appear to hold valid representation of the destination type.float
stof
(string str)
Convert/decode the initial part of
str
to afloat
representation. The return value will be0
if the string doesn’t appear to hold valid representation of the destination type.string
substr
(string str, output string results[], string sep, int maxsplit)
string
substr
(string str, output string results[], string sep)
string
substr
(string str, output string results[])
Fills the
result
array with the words in the stringstr
, usingsep
as the delimiter string. Ifmaxsplit
is supplied, at mostmaxsplit
splits are done. Ifsep
is""
(or if not supplied), any whitespace string is a separator. The value returned is the number of elements (separated strings) written to theresults
array.string
substr
(string s, int start, int length)
string
substr
(string s, int start)
Return at most
length
characters froms
, starting with the character indexed bystart
(beginning with 0). Iflength
is omitted, return the rest ofs
, starting withstart
. Ifstart
is negative, it counts backwards from the end of the string (for example,substr(s,1)
returns just the last character ofs
).int
getchar
(string s, int n)
Returns the numeric value of the \(n^{\mathrm{th}}\) character of the string, or
0
ifN
does not index a valid character of the string.int
hash
(string s)
Returns a deterministic, repeatable hash of the string.
int
regex_search
(string subject, string regex)
int
regex_search
(string subject, int results[], string regex)
Returns 1 if any substring of
subject
matches a standard POSIX regular expressionregex
, 0 if it does not.In the form that also supplies a
results
array, when a match is found, the array will be filled in as follows:results[0]
the character index of the start of the sequence that matched the regular expression.
results[1]
the character index of the end (i.e., one past the last matching character) of the sequence that matched the regular expression.
results[
\(2i\)]
the character index of the start of the sequence that matched subexpression \(i\) of the regular expression.
results[
\(2i+1\)]
the character index of the end (i.e., one past the last matching character) of the sequence that matched subexpression \(i\) of the regular expression.
Subexpressions are denoted by surrounding them in parentheses in the regular expression.
A few examples illustrate regular expression searching:
r = regex_search ("foobar.baz", "bar"); // = 1 r = regex_search ("foobar.baz", "bark"); // = 0 int match[2]; regex_search ("foobar.baz", match, "[Oo]{2}") = 1 (match[0] == 1, match[1] == 3) substr ("foobar.baz", match[0], match[1]match[0]) = "oo" int match[6]; regex_search ("foobar.baz", match, "(f[Oo]{2}).*(.az)") = 1 substr ("foobar.baz", match[0], match[1]match[0]) = "foobar.baz" substr ("foobar.baz", match[2], match[3]match[2]) = "foo" substr ("foobar.baz", match[4], match[5]match[4]) = "baz"
int
regex_match
(string subject, string regex)
int
regex_match
(string subject, int results[], string regex)
Identical to
regex_search
, except that it must match the wholesubject
string, not merely a substring.
7.9. Texture#
type
texture
(string filename, float s, float t,
...params...
)
type
texture
(string filename, float s, float t,
\(~~~~~~~~~~~~~~~~~~~~~~~\)float dsdx, float dtdx, float dsdy, float dtdy,
...params...
)
Perform a texture lookup of an image file, indexed by 2D coordinates (
s
,t
), antialiased over a region defined by the differentialsdsdx
,dtdx
,dsdy
anddtdy
(which are computed automatically froms
andt
, if not supplied). Whether the results are assigned to afloat
or acolor
(or type cast to one of those) determines whether the texture lookup is a single channel or three channels.The 2D lookup coordinate(s) may be followed by optional keyvalue arguments (see Section Function calls) that control the behavior of
texture()
:"blur",
float
Additional blur when looking up the texture value (default: 0). The blur amount is relative to the size of the texture (i.e., 0.1 blurs by a kernel that is 10% of the full width and height of the texture).
The blur may be specified separately in the
s
andt
directions by using the"sblur"
and"tblur"
parameters, respectively."width",
float
Scale (multiply) the size of the filter as defined by the differentials (or implicitly by the differentials of
s
andt
). The default is1
, meaning that no special scaling is performed. A width of0
would effectively turn off texture filtering entirely.The width value may be specified separately in the
s
andt
directions by using the"swidth"
and"twidth"
parameters, respectively."wrap",
string
Specifies how the texture wraps coordinates outside the \([0,1]\) range. Supported wrap modes include:
"black"
,"periodic"
,"clamp"
,"mirror"
, and"default"
(which is the default). A value of"default"
indicates that the renderer should use any wrap modes specified in the texture file itself (a non"default"
value overrides any wrap mode specified by the file).The wrap modes may be specified separately in the
s
andt
directions by using the"swrap"
and"twrap"
parameters, respectively."firstchannel",
int
The first channel to look up from the texture map (default: 0).
"subimage",
int
“subimage",
string
Specify the subimage (by numerical index, or name) of the subimage within a multiimage texture file (default: subimage 0).
"fill",
float
The value to return for any channels that are requested, but not present in the texture file (default: 0).
"missingcolor",
color
,"missingalpha",
float
If present, supplies a missing color (and alpha value) that will be used for missing or broken textures – instead of treating it as an error. If you want a missing or broken texture to be reported as an error, you must not supply the optional
"missingcolor"
parameter."alpha",
floatvariable
The alpha channel (presumed to be the next channel following the channels returned by the
texture()
call) will be stored in the variable specified. This allows for RGBA lookups in a single call totexture()
."errormessage",
stringvariable
If this option is supplied, any error messages generated by the texture system will be stored in the specified variable rather than issuing error calls to the renderer, thus leaving it up to the shader to handle any errors. The error message stored will be
""
if no error occurred."interp",
string
Overrides the texture interpolation method:
"smartcubic"
(the default),"cubic"
,"linear"
, or"closest"
.
type
texture3d
(string filename, point p,
...params...
)
type
texture3d
(string filename, point p, vector dpdx, vector dpdy, vector dpdz,
...params...
)
Perform a 3D lookup of a volume texture, indexed by 3D coordinate
p
, antialiased over a region defined by the differentialsdpdx
,dpdy
, anddpdz
(which are computed automatically fromp
, if not supplied). Whether the results are assigned to afloat
or acolor
(or type cast to one of those) determines whether the texture lookup is a single channel or three channels.The
p
coordinate (anddpdx
,dpdy
, anddpdz
derivatives, if supplied) are assumed to be in “common” space and will be automatically transformed into volume local coordinates, if such a transormation is specified in the volume file itself.The 3D lookup coordinate may be followed by optional token/value arguments that control the behavior of
texture3d()
:"blur"
,float
Additional blur when looking up the texture value (default: 0). The blur amount is relative to the size of the texture (i.e., 0.1 blurs by a kernel that is 10% of the full width, height, and depth of the texture).
The blur may be specified separately in the
s
,t
, andr
directions by using the"sblur"
,"tblur"
, and"rblur"
parameters, respectively."width"
,float
Scale (multiply) the size of the filter as defined by the differentials (or implicitly by the differentials of
s
,t
, andr
). The default is1
, meaning that no special scaling is performed. A width of0
would effectively turn off texture filtering entirely.The width value may be specified separately in the
s
,t
, andr
directions by using the"swidth"
,"twidth"
, and"rwidth"
parameters, respectively."wrap"
,string
Specifies how the texture wraps coordinates outside the \([0,1]\) range. Supported wrap modes include:
"black"
,"periodic"
,"clamp"
,"mirror"
, and"default"
(which is the default). A value of"default"
indicates that the renderer should use any wrap modes specified in the texture file itself (a non"default"
value overrides any wrap mode specified by the file).The wrap modes may be specified separately in the
s
,t
, andr
directions by using the"swrap"
,"twrap"
, and"rwrap"
parameters, respectively."firstchannel"
,int
The first channel to look up from the texture map (default: 0).
"subimage"
,int
"subimage"
,string
Specify the subimage (by numerical index, or name) of the subimage within a multiimage texture file (default: subimage 0).
"fill"
,float
The value to return for any channels that are requested, but not present in the texture file (default: 0).
"missingcolor"
,color
,"missingalpha"
,float
If present, supplies a missing color (and alpha value) that will be used for missing or broken textures – instead of treating it as an error. If you want a missing or broken texture to be reported as an error, you must not supply the optional
"missingcolor"
parameter."time"
,float
A time value to use if the volume texture specifies a timevarying local transformation (default: 0).
"alpha"
,floatvariable
The alpha channel (presumed to be the next channel following the channels returned by the
texture3d()
call) will be stored in the variable specified. This allows for RGBA lookups in a single call totexture3d()
."errormessage"
, ‘stringvariable’If this option is supplied, any error messages generated by the texture system will be stored in the specified variable rather than issuing error calls to the renderer, thus leaving it up to the shader to handle any errors. The error message stored will be
""
if no error occurred.
type
environment
(string filename, vector R,
...params...
)
type
environment
(string filename, vector R, vector dRdx, vector dRdy,
...params...
)
Perform an environment map lookup of an image file, indexed by direction
R
, antialiased over a region defined by the differentialsdRdx
,dRdy
(which are computed automatically fromR
, if not supplied). Whether the results are assigned to afloat
or acolor
(or type cast to one of those) determines whether the texture lookup is a single channel or three channels.The lookup direction (and optional derivatives) may be followed by optional token/value arguments that control the behavior of
environment()
: “blur”,
float
Additional blur when looking up the texture value (default: 0). The blur amount is relative to the size of the texture (i.e., 0.1 blurs by a kernel that is 10% of the full width and height of the texture).
The blur may be specified separately in the
s
andt
directions by using the"sblur"
and"tblur"
parameters, respectively. “width”,
float
Scale (multiply) the size of the filter as defined by the differentials (or implicitly by the differentials of
s
andt
). The default is1
, meaning that no special scaling is performed. A width of0
would effectively turn off texture filtering entirely.The width value may be specified separately in the
s
andt
directions by using the"swidth"
and"twidth"
parameters, respectively. “firstchannel”,
int
The first channel to look up from the texture map (default: 0).
 “fill”,
float
The value to return for any channels that are requested, but not present in the texture file (default: 0).
 “missingcolor”,
color
, “missingalpha”,float
If present, supplies a missing color (and alpha value) that will be used for missing or broken textures – instead of treating it as an error. If you want a missing or broken texture to be reported as an error, you must not supply the optional
"missingcolor"
parameter. “alpha”,
floatvariable
The alpha channel (presumed to be the next channel following the channels returned by the
environment()
call) will be stored in the variable specified. This allows for RGBA lookups in a single call toenvironment()
. “errormessage”,
stringvariable
If this option is supplied, any error messages generated by the texture system will be stored in the specified variable rather than issuing error calls to the renderer, thus leaving it up to the shader to handle any errors. The error message stored will be
""
if no error occurred.
 “blur”,
int
gettextureinfo
(string texturename, string paramname, output
type
destination)
int
gettextureinfo
(string texturename, float s, float t, string paramname, output
type
destination)
Retrieves a parameter from a named texture file. If the file is found, and has a parameter that matches the name and type specified, its value will be stored in
destination
andgettextureinfo()
will return1
. If the file is not found, or doesn’t have a matching parameter (including if the type does not match),destination
will not be modified andgettextureinfo()
will return0
.The version of
gettextureinfo()
that takess
andt
parameters retrieves information about the texture file that will be used for those texture coordinates. This can be useful for UDIM textures that may use different texture files for different regions, based on the corodinates. For regular, nonUDIM textures, the coordinates, if supplied, will be ignored. When UDIM textures are queried without coordinates supplied, it will succeed and return the texture info only if that parameter is found and has the same value in all files comprising the UDIM set. (Note: the version with coordinates was added in OSL 1.12.)Valid parameters recognized are listed below:
Name
Type
Description
"exists"
int
Result is 1 if the file exists and is an texture format that OSL can read, or 0 if the file does not exist, or could not be properly read as a texture. Note that unlike all other queries, this query will “succeed” (return
1
) if the file does not exist."resolution"
int[2]
The resolution (\(x\) and \(y\)) of the highest MIPmap level stored in the texture map.
"resolution"
int[3]
The resolution (\(x\), \(y\), and \(z\)) of the highest MIPmap level stored in the 3D texture map. If it isn’t a volumetric texture, the third component (
z
resolution) will be 1."channels"
int
The number of channels in the texture map.
"type"
string
Returns the semantic type of the texture, one of:
"Plain Texture"
,"Shadow"
,"Environment"
,Volume Texture"
."subimages"
int
Returns the number of subimages in the texture file.
"textureformat"
string
Returns the texture format, one of: “
Plain Texture
”, “Shadow
”, “CubeFace Shadow
”, “Volume Shadow
”, “CubeFace Environment
”, “LatLong Environment
”, “Volume Texture
”. Note that this differs from"type"
in that it specifically distinguishes between the different types of shadows and environment maps."datawindow"
int[]
Returns the pixel data window of the image. The argument is an
int
array either of length 4 or 6, in which will be placed the (xmin, ymin, xmax, ymax) or (xmin, ymin, zmin, xmax, ymax, zmax), respectively. (N.B. thez
values may be useful for 3D/volumetric images; for 2D images they will be 0)."displaywindow"
int[]
Returns the display (a.k.a. full) window of the image. The argument is an
int
array either of length 4 or 6, in which will be placed the (xmin, ymin, xmax, ymax) or (xmin, ymin, zmin, xmax, ymax, zmax), respectively. (N.B. thez
values may be useful for 3D/volumetric images; for 2D images they will be 0)."worldtocamera"
matrix
If the texture is a rendered image, retrieves the worldtocamera 3D transformation matrix that was used when it was created.
"worldtoscreen"
matrix
If the texture is a rendered image, retrieves the matrix that projected points from world space into a 2D screen coordinate system where \(x\) and \(y\) range from \(1\) to \(+1\).
"averagecolor"
color
Retrieves the average color (first three channels) of the texture.
"averagealpha"
float
Retrieves the average alpha (the channel with
"A"
name) of the texture.anything else
any
Searches for matching name and type in the metadata or other header information of the texture file.
int
pointcloud_search
(string ptcname, point pos, float radius, int maxpoints, [int sort,] string attr, Type data[], ..., string attrN, Type dataN[] )
Search the named point cloud for the
maxpoints
closest points topos
within the givenradius
, returning the values of any named attributes of those points in the the givendata
arrays. If the optionalsort
parameter is present and is nonzero, the ordering of the points found will be sorted by distance frompos
, from closest to farthest; otherwise, the results are guaranteed to be themaxpoints
closest topos
, but not necessarily sorted by distance (this may be faster for some implementations than when sorted results are required). The return value is the number of points returned, ranging from 0 (nothing found in the neighborhood) to the lesser ofmaxpoints
and the actual lengths of the arrays (the arrays will never be written beyond their actual length).These attribute names are reserved:
Name
Type
Description
“
position
”point
The position of each point
“
distance
”float
The distance between the point and
pos
“
index
”int
The point’s unique index within the cloud
Note that the named point cloud will be created, if it does not yet exist in memory, and that it will be initialized by reading a point cloud from disk, if there is one matching the name.
Generally, the element type of the data arrays must match exactly the type of the point data attribute, or else you will get a runtime error. But there are two exceptions: (1) “triple” types (
color
,point
,vector
,normal
) are considered interchangeable; and (2) it is legal to retrievefloat
arrays (e.g., a point cloud attribute that isfloat[4]
) into a regular array offloat
, and the results will simply be concatenated into the larger array (which must still be big enough, in total, to holdmaxpoints
of the data type in the file).Example:
float r = 3.0; point pos[10]; color col[10]; int n = pointcloud_search ("particles.ptc", P, r, 10, "position", pos, "color", col); printf ("Found %d particles within radius %f of (%p)\n", r, P); for (int i = 0; i < n; ++i) printf (" position (%f) > color (%g)\n", pos[i], col[i]);
int
pointcloud_get
(string ptcname, int indices[], int count, string attr,
type
data[])
Given a point cloud and a list of points
indices[0..count1]
, store the attribute named byattr
for each point, respectively, indata[0..count1]
. Return 1 if successful, 0 for failure, which could include the attribute not matching the type ofdata
, invalid indices, or an unknown point cloud file.This can be used in conjunction with
pointcloud_search()
, as in the following example:float r = 3.0; int indices[10]; int n = pointcloud_search ("particles.ptc", P, r, 10, "index", indices); float temp[10]; // presumed to be "float" attribute float quaternions[40]; // presumed to be "float[4]" attribute int ok = pointcloud_get ("particles.ptc", indices, n, "temperature", temp, "quat", quaternions);
As with
pointcloud_search
, the element type of the data array must either be equivalent to the point cloud attribute being retrieved, or else when retrievingfloat
arrays (e.g., a point cloud attribute that isfloat[4]
) into a regular array offloat
, and the results will simply be concatenated into the larger array (which must still be big enough, in total, to holdmaxpoints
of the data type in the file).int
pointcloud_write
(string ptcname, point pos, string attr1,
type
data1, ...)
Save the tuple (
attr1
,data1
, …,attrN
,dataN
) at positionpos
in a named point cloud. The point cloud will be saved when the frame is finished computing. Return 1 if successful, 0 for failure, which could include the attributes not matching names or types at different positions in the point cloud.Example:
color C = ...; int ok = pointcloud_write ("particles.ptc", P, "normal", N, "color", C);
7.10. Material Closures#
For closure color
functions, the return “value” is symbolic and may be
passed to an output variable or assigned to Ci
, to be evaluated at a later
time convenient to the renderer in order to compute the exitant radiance in
the direction I
. But the shader itself cannot examine the numeric values
of the closure color
.
The intent of this specification is to give a minimal but useful set of
material closures that you can expect any renderer implementation to provide.
Individual renderers may supply additional closures that are specific to the
workings of that renderer. Additionally, individual renderers may allow
additional parameters or controls on the standard closures, passed as
token/value pairs following the required arguments (much like the optional
arguments to the texture()
function). Consult the documentation for your
specific renderer for details.
OSL’s standard material closures are by synchronized to match the names and properties of the physicallybased shading nodes of MaterialX v1.38 (https://www.materialx.org/).
Surface BSDF closures#
closure color
oren_nayar_diffuse_bsdf
(normal N, color albedo, float roughness)
Constructs a diffuse reflection BSDF based on the OrenNayar reflectance model.
Parameters include:
N
Normal vector of the surface point being shaded.
albedo
Surface albedo.
roughness
Surface roughness [0,1]. A value of 0.0 gives Lambertian reflectance.
The OrenNayar reflection model is described in M. Oren and S. K. Nayar, “Generalization of Lambert’s Reflectance Model,” Proceedings of SIGGRAPH 1994, pp.239246 (July, 1994).
closure color
burley_diffuse_bsdf
(normal N, color albedo, float roughness)
Constructs a diffuse reflection BSDF based on the corresponding component of the Disney Principled shading model.
Parameters include:
N
Normal vector of the surface point being shaded.
albedo
Surface albedo.
roughness
Surface roughness [0,1]. A value of 0.0 gives Lambertian reflectance.
closure color
dielectric_bsdf
(normal N, vector U, color reflection_tint, color transmission_tint, float roughness_x, float roughness_y, float ior, string distribution)
Constructs a reflection and/or transmission BSDF based on a microfacet reflectance model and a Fresnel curve for dielectrics. The two tint parameters control the contribution of each reflection/transmission lobe. The tints should remain 100% white for a physically correct dielectric, but can be tweaked for artistic control or set to 0.0 for disabling a lobe.
The closure may be vertically layered over a base BSDF for the surface beneath the dielectric layer. This is done using the
layer()
closure. By chaining multipledielectric_bsdf
closures you can describe a surface with multiple specular lobes. If transmission is enabled (transmission_tint
\(>\) 0.0) the closure may be layered over a VDF closure describing the surface interior to handle absorption and scattering inside the medium.Parameters include:
N
Normal vector of the surface point being shaded.
U
Tangent vector of the surface point being shaded.
reflection_tint
Weight per color channel for the reflection lobe. Should be (1,1,1) for a physicallycorrect dielectric surface, but can be tweaked for artistic control. Set to (0,0,0) to disable reflection.
transmission_tint
Weight per color channel for the transmission lobe. Should be (1,1,1) for a physicallycorrect dielectric surface, but can be tweaked for artistic control. Set to (0,0,0) to disable transmission.
roughness_x
Surface roughness in the U direction with a perceptually linear response over its range.
roughness_y
Surface roughness in the V direction with a perceptually linear response over its range.
ior
Refraction index.
distribution
Microfacet distribution. An implementation is expected to support the following distributions:
"ggx"
thinfilm_thickness
Optional float parameter for thickness of an iridescent thin film layer on top of this BSDF. Given in nanometers.
thinfilm_ior
Optional float parameter for refraction index of the thin film layer.
closure color
conductor_bsdf
(normal N, vector U, float roughness_x, float roughness_y, color ior, color extinction, string distribution)
Constructs a reflection BSDF based on a microfacet reflectance model. Uses a Fresnel curve with complex refraction index for conductors/metals. If an artistic parametrization is preferred the
artistic_ior()
utility function can be used to convert from artistic to physical parameters.Parameters include:
N
Normal vector of the surface point being shaded.
U
Tangent vector of the surface point being shaded.
roughness_x
Surface roughness in the U direction with a perceptually linear response over its range.
roughness_y
Surface roughness in the V direction with a perceptually linear response over its range.
ior
Refraction index.
extinction
Extinction coefficient.
distribution
Microfacet distribution. An implementation is expected to support the following distributions:
"ggx"
thinfilm_thickness
Optional float parameter for thickness of an iridescent thin film layer on top of this BSDF. Given in nanometers.
thinfilm_ior
Optional float parameter for refraction index of the thin film layer.
closure color
generalized_schlick_bsdf
(normal N, vector U, color reflection_tint, color transmission_tint, float roughness_x, float roughness_y, color f0, color f90, float exponent, string distribution)
Constructs a reflection and/or transmission BSDF based on a microfacet reflectance model and a generalized Schlick Fresnel curve. The two tint parameters control the contribution of each reflection/transmission lobe.
The closure may be vertically layered over a base BSDF for the surface beneath the dielectric layer. This is done using the layer() closure. By chaining multiple
dielectric_bsdf
closures you can describe a surface with multiple specular lobes. If transmission is enabled (transmission_tint
\(>\) 0.0) the closure may be layered over a VDF closure describing the surface interior to handle absorption and scattering inside the medium.Parameters include:
N
Normal vector of the surface point being shaded.
U
Tangent vector of the surface point being shaded.
reflection_tint
Weight per color channel for the reflection lobe. Set to (0,0,0) to disable reflection.
transmission_tint
Weight per color channel for the transmission lobe. Set to (0,0,0) to disable transmission.
roughness_x
Surface roughness in the U direction with a perceptually linear response over its range.
roughness_y
Surface roughness in the V direction with a perceptually linear response over its range.
f0
Reflectivity per color channel at facing angles.
f90
Reflectivity per color channel at grazing angles.
exponent
Variable exponent for the Schlick Fresnel curve, the default value should be 5.
distribution
Microfacet distribution. An implementation is expected to support the following distributions:
"ggx"
thinfilm_thickness
Optional float parameter for thickness of an iridescent thin film layer on top of this BSDF. Given in nanometers.
thinfilm_ior
Optional float parameter for refraction index of the thin film layer.
closure color
translucent_bsdf
(normal N, color albedo)
Constructs a translucent (diffuse transmission) BSDF based on the Lambert reflectance model.
Parameters include:
N
Normal vector of the surface point being shaded.
albedo
Surface albedo.
roughness
Surface roughness [0,1]. A value of 0.0 gives Lambertian reflectance.
closure color
transparent_bsdf
( )
Constructs a closure that represents straight transmission through a surface.
closure color
subsurface_bssrdf
( )
Constructs a BSSRDF for subsurface scattering within a homogeneous medium.
Parameters include:
N
Normal vector of the surface point being shaded.
albedo
Singlescattering albedo of the medium.
transmission_depth
Distance travelled inside the medium by white light before its color becomes transmission_color by Beer’s law. Given in scene length units, range [0,infinity). Together with transmission_color this determines the extinction coefficient of the medium.
transmission_color
Desired color resulting from white light transmitted a distance of ‘transmission_depth’ through the medium. Together with transmission_depth this determines the extinction coefficient of the medium.
anisotropy
Scattering anisotropy [1,1]. Negative values give backwards scattering, positive values give forward scattering, and 0.0 gives uniform scattering.
closure color
sheen_bsdf
(normal N, color albedo, float roughness)
Constructs a microfacet BSDF for the backscattering properties of clothlike materials. This closure may be vertically layered over a base BSDF, where energy that is not reflected will be transmitted to the base closure.
Parameters include:
N
Normal vector of the surface point being shaded.
albedo
Surface albedo.
roughness
Surface roughness [0,1].
Volumetric material closures#
closure color
anisotropic_vdf
(color albedo, color extinction, float anisotropy)
Constructs a VDF scattering light for a general participating medium, based on the HenyeyGreenstein phase function. Forward, backward and uniform scattering is supported and controlled by the anisotropy input.
Parameters include:
albedo
Singlescattering albedo of the medium.
extinction
Volume extinction coefficient.
anisotropy
Scattering anisotropy [1,1]. Negative values give backwards scattering, positive values give forward scattering, and 0.0 gives uniform scattering.
closure color
medium_vdf
(color albedo, float transmission_depth, color transmission_color, float anisotropy, float ior, int priority)
Constructs a VDF for light passing through a dielectric homogeneous medium, such as glass or liquids. The parameters
transmission_depth
andtransmission_color
control the extinction coefficient of the medium in an artistfriendly way. A priority can be set to determine the ordering of overlapping media.Parameters include:
albedo
Singlescattering albedo of the medium.
transmission_depth
Distance travelled inside the medium by white light before its color becomes transmission_color by Beer’s law. Given in scene length units, range [0,infinity). Together with transmission_color this determines the extinction coefficient of the medium.
transmission_color
Desired color resulting from white light transmitted a distance of ‘transmission_depth’ through the medium. Together with transmission_depth this determines the extinction coefficient of the medium.
anisotropy
Scattering anisotropy [1,1]. Negative values give backwards scattering, positive values give forward scattering, and 0.0 gives uniform scattering.
ior
Refraction index of the medium.
priority
Priority of this medium (for nested dielectrics).
Light emission closures#
closure color
uniform_edf
(color emittance)
Constructs an EDF emitting light uniformly in all directions. This is used to represent a glowing/emissive material. When called in the context of a surface shader group, it implies that light is emitted in a full hemisphere centered around the surface normal. When called in the context of a volume shader group, it implies that light is emitted evenly in all directions around the point being shaded.
The
emittance
parameter is the amount of emission and has units of radiance (e.g., \(\mathrm{W}\cdot\mathrm{sr}^{1}\cdot\mathrm{m}^{2}\)). This means that a surface directly seen by the camera will directly reproduce the closure weight in the final pixel, regardless of being a surface or a volume.For an emissive surface, if you divide the return value of
uniform_edf()
bysurfacearea() * M_PI
, then you can easily specify the total emissive power of the light (e.g., \(\mathrm{W}\)), regardless of its physical size.
Layering and Signaling closures#
closure color
layer
(closure color top, closure color base)
Vertically layer a layerable BSDF such as
dielectric_bsdf
,generalized_schlick_bsdf
orsheen_bsdf
over a BSDF or VDF. The implementation is target specific, but a standard way of handling this is by albedo scaling, usingbase*(1reflectance(top)) + top
, wherereflectance()
calculates the directional albedo of a given top BSDF.closure color
holdout
( )
Returns a
closure color
that does not represent any additional light reflection from the surface, but does signal to the renderer that the surface is a holdout object (appears transparent in the final output yet hides objects behind it). “Partial holdouts” may be designated by weighting theholdout()
closure by a weight that is less than 1.0.closure color
debug
(string outputname)
Returns a
closure color
that does not represent any additional light reflection from the surface, but does signal to the renderer to add the weight of the closure (which may be afloat
or acolor
) to the named output (i.e., AOV).
Material utility functions#
void
artistic_ior
(color reflectivity, color edge_tint, output color ior, output color extinction)
Converts the artistic parameterization reflectivity and edge_tint to complex IOR values. To be used with the
conductor_bsdf()
closure.Parameters include:
reflectivity
Reflectivity per color channel at facing angles (\(r\) parameter in [OG14])
edge_tint
Color bias for grazing angles (\(g\) parameter in [OG14]). NOTE: This is not equal to ‘f90’ in a Schlick Fresnel parameterization.
ior
Output refraction index.
extinction
Output extinction coefficient.
Reference: [OG14] Ole Gulbrandsen, “Artist Friendly Metallic Fresnel”, Journal of Computer Graphics Tools 3(4), 2014. http://jcgt.org/published/0003/04/03/paper.pdf
Deprecated closures#
These were described in the original OSL language specification, but beginning with OSL 1.12, these are considered deprecated. Support for them will be removed entirely in OSL 2.0.
Deprecated Surface closures#
closure color
diffuse
(normal N)
Returns a
closure color
that represents the Lambertian diffuse reflectance of a smooth surface,\[ \int_{\Omega}{\frac{1}{\pi} \max(0, N \cdot \omega) Cl(P,\omega) d\omega} \]where \(N\) is the unitlength forwardfacing surface normal at
P
, \(\Omega\) is the set of all outgoing directions in the hemisphere surrounding \(N\), and \(Cl(P,\omega)\) is the incident radiance atP
coming from the direction \(\omega\).closure color
phong
(normal N, float exponent)
Returns a
closure color
that represents specular reflectance of the surface using the Phong BRDF. Theexponent
parameter indicates how smooth or rough the material is (higherexponent
values indicate a smoother surface).closure color
oren_nayar
(normal N, float sigma)
Returns a
closure color
that represents the diffuse reflectance of a rough surface, implementing the OrenNayar reflectance formula. Thesigma
parameter indicates how smooth or rough the microstructure of the material is, with 0 being perfectly smooth and giving an appearance identical todiffuse()
.The OrenNayar reflection model is described in M. Oren and S. K. Nayar, “Generalization of Lambert’s Reflectance Model,” Proceedings of SIGGRAPH 1994, pp.239246 (July, 1994).
closure color
ward
(normal N, vector T, float xrough, float yrough)
Returns a
closure color
that represents the anisotropic specular reflectance of the surface atP
. TheN
andT
vectors, both presumed to be unitlength, are the surface normal and tangent, used to establish a local coordinate system for the anisotropic effects. Thexrough
andyrough
specify the amount of roughness in the tangent (T
) and bitangent (N
\(\times\)T
) directions, respectively.The Ward BRDF is described in Ward, G., “Measuring and Modeling Anisotropic Reflection,” Proceedings of SIGGRAPH 1992.
closure color
microfacet
(string distribution, normal N, float alpha, float eta, int refract)
Returns a
closure color
that represents scattering on the surface using some microfacet distribution. A simplified isotropic version of the previous function.closure color
reflection
(normal N, float eta)
Returns a
closure color
that represents sharp mirrorlike reflection from the surface. The reflection direction will be automatically computed based on the incident angle. Theeta
parameter is the index of refraction of the material. Thereflection()
closure behaves as if it were implemented as follows:vector R = reflect (I, N); return raytrace (R);
closure color
refraction
(normal N, float eta)
Returns a
closure color
that represents sharp glasslike refraction of objects “behind” the surface. Theeta
parameter is the ratio of the index of refraction of the medium on the “inside” of the surface divided by the index of refration of the medium on the “outside” of the surface. The “outside” direction is the one specified byN
.The refraction direction will be automatically computed based on the incident angle and
eta
, and the radiance returned will be automatically scaled by the Fresnel factor for dielectrics. Therefraction()
closure behaves as if it were implemented as follows:float Kr, Kt; vector R, T; fresnel (I, N, eta, Kr, Kt, R, T); return Kt * raytrace (T);
closure color
transparent
( )
Returns a
closure color
that shows the light behind the surface without any refractive bending of the light directions. Thetransparent()
closure behaves as if it were implemented as follows:return raytrace (I);
closure color
translucent
( )
Returns a
closure color
that represents the Lambertian diffuse translucence of a smooth surface, which is much likediffuse()
except that it gathers light from the far side of the surface. Thetranslucent()
closure behaves as if it were implemented as follows:return diffuse (N);
Deprecated Volumetric closures#
closure color
isotropic
( )
Returns a
closure color
that represents the scattering of an isotropic volumetric material, scattering light evenly in all directions, regardless of its original direction.closure color
henyey_greenstein
(float g)
Returns a
closure color
that represents the directional volumetric scattering by small suspended particles. Theg
parameter is the anisotropy factor, in the range \((1, 1)\), with positive values indicating predominantly forwardscattering, negative values indicating predominantly backscattering, and value of \(g=0\) resulting in isotropic scattering.closure color
absorption
( )
Returns a
closure color
that does not represent any additional light scattering, but rather signals to the renderer the absorption represents the scattering of an isotropic volumetric material, scattering light evenly in all directions, regardless of its original direction.
Deprecated Emission closures#
closure color
emission
( )
Returns a
closure color
that represents a glowing/emissive material. When called in the context of a surface shader group, it implies that light is emitted in a full hemisphere centered around the surface normal. When called in the context of a volume shader group, it implies that light is emitted evenly in all directions around the point being shaded.The weight of the emission closure has units of radiance (e.g., \(\mathrm{W}\cdot\mathrm{sr}^{1}\cdot\mathrm{m}^{2}\)). This means that a surface directly seen by the camera will directly reproduce the closure weight in the final pixel, regardless of being a surface or a volume.
For an emissive surface, if you divide the return value of
emission()
bysurfacearea() * M_PI
, then you can easily specify the total emissive power of the light (e.g., \(\mathrm{W}\)), regardless of its physical size.closure color
background
( )Returns a
closure color
that represents the radiance of the “background” infinitely far away in the view direction. The implementation is rendererspecific, but often involves looking up from an HDRI environment map.
7.11. Renderer state and message passing#
int
getattribute
(string name, output
type
destination)
int
getattribute
(string name, int arrayindex, output
type
destination)
int
getattribute
(string object, string name, output
type
destination)
int
getattribute
(string object, string name, int arrayindex, output
type
destination)
Retrieves a named renderer attribute or the value of an interpolated geometric variable. If an object is explicitly named, that is the only place that will be searched (
"global"
means the global scenewide attributes). For the forms of the function with no object name, or if the object name is the empty string""
, the renderer will first search perobject attributes on the current object (or interpolated variables with that name attached to the object), then if not found it will search global scenewide attributes.If the attribute is found and can be converted to the type of
destination
, the attribute’s value will be stored indestination
andgetattribute
will return1
. If not found, or the type cannot be converted,destination
will not be modified andgetattribute
will return0
.The automatic type conversions include those that are allowed by assignment in OSL source code:
int
tofloat
,float
toint
(truncation),float
(orint
) to triple (replicating the value), any triple to any other triple. Additionally, the following conversions which are not allowed by assignment in OSL source code will also be performed by this call:float
(orint
) tofloat[2]
(replication into both array elements),float[2]
to triple (setting the third component to 0).The forms of this function that have the the
arrayindex
parameter will retrieve the individual indexed element of the named array. In this case,name
must be an array attribute, the type ofdestination
must be the type of the array element (not the type of the whole array), and the value ofarrayindex
must be a valid index given the array’s size.Tables giving “standardized” names for different kinds of attributes may be found below. All renderers are expected to use the same names for these attributes, but are free to choose any names for additional attributes they wish to make queryable.
Names of standard attributes that may be retrieved:
Name
Type
Description
"osl:version"
int
Major x 10000 + Minor x 100 + patch.
"shader:shadername"
string
Name of the shader master.
"shader:layername"
string
Name of the layer instance.
"shader:groupname"
string
Name of the shader group.
Names of standard camera attributes that may be retrieved are in the table below. If the
getattribute()
function specifies anobjectname
parameter and it is the name of a valid camera, the value specific to that camera is retrieved. If no specific camera is named, the global or default camera is implied.Name
Type
Description
"camera:resolution"
int[2]
Image resolution.
"camera:pixelaspect"
float
Pixel aspect ratio.
"camera:projection"
string
Projection type (e.g.,
"perspective"
,"orthographic"
, etc.)"camera:fov"
float
Field of fiew.
"camera:clip_near"
float
Near clip distance.
"camera:clip_far"
float
Far clip distance.
"camera:clip"
float[2]
Near and far clip distances.
"camera:shutter_open"
float
Shutter open time.
"camera:shutter_close"
float
Shutter close time.
"camera:shutter"
float[2]
Shutter open and close times.
"camera:screen_window"
float[4]
Screen window (xmin, ymin, xmax, ymax).
void
setmessage
(string name, output
type
value)
Store a name/value pair in an area where it can later be retrieved by other shaders attached to the same object. If there is already a message with the same name attached to this shader invocation, it will be replaced by the new value. The message
value
may be any basic scalar type, array, or closure, but may not be astruct
.int
getmessage
(string name, output
type
destination)
int
getmessage
(string source, string name, output
type
destination)
Retrieve a message from another shader attached to the same object. If a message is found with the given name, and whose type matches that of
destination
, the value will be stored indestination
andgetmessage()
will return1
. If no message is found that matches both the name and type,destination
will be unchanged andgetmessage()
will return0
.The
source
, if supplied, designates from where the message should be retrieved, and may have any of the following values:"trace"
Retrieves data about the object hit by the last
trace
call made. Data recognized include:Name
Type
Description
"hit"
int
Zero if the ray hit nothing, 1 if it hit.
"hitdist"
float
The distance to the hit.
"geom:name"
string
The name of the object hit.
other
Retrieves the named global (
P
,N
, etc.), shader parameter, or set message of the closest object hit (only if it was a shaded ray).
Note that which information may be retrieved depends on whether the ray was traced with the optional
"shade"
parameter indicating whether or not the shader ought to execute on the traced ray. If"shade"
was 0, you may retrieve “globals” (P
,N
, etc.), interpolated vertex variables, shader instance values, or graphics state attributes (object name, etc.). But"shade"
must be nonzero to correctly retrieve shader output variables or messages that are set by the shader (viasetmessage()
).
float
surfacearea
( )
Returns the surface area of the area light geometry being shaded. This is meant to be used in conjunction with
emission()
in order to produce the correct emissive radiance given a user preference for a total wattage for the area light source. The value of this function is not expected to be meaningful for nonlight shaders.int
raytype
(string name)
Returns 1 if ray being shaded is of the given type, or 0 if the ray is not of that type or if the ray type name is not recognized by the renderer.
The set of ray type names is customizeable for renderers supporting OSL, but is expected to include at a minimum
"camera"
,"shadow"
,"diffuse"
,"glossy"
,"reflection"
,"refraction"
. They are not necessarily mutually exclusive, with the exception that camera rays should be of class"camera"
and no other.int
backfacing
( )
Returns 1 if the surface is being sampled as if “seen” from the back of the surface (or the “inside” of a closed object). Returns 0 if seen from the “front” or the “outside” of a closed object.
int
isconnected
(
type
parameter)
Returns 1 if the argument is a shader parameter and is connected to an earlier layer in the shader group, 2 if the argument is a shader output parameter connected to a later layer in the shader group, 3 if connected to both earlier and later layers, otherwise returns 0. Remember that function arguments in OSL are always passbyreference, so
isconnected()
applied to a function parameter will depend on what was passed in as the actual parameter.int
isconstant
(
type
expr)
Returns 1 if the expression can, at runtime (knowing the values of all the shader group’s parameter values and connections), be discerned to be reducible to a constant value, otherwise returns 0.
This is primarily a debugging aid for advanced shader writers to verify their assumptions about what expressions can end up being constantfolded by the runtime optimizer.
7.12. Dictionary Lookups#
int
dict_find
(string dictionary, string query)
int
dict_find
(int nodeID, string query)
Find a node in the dictionary by a query. The
dictionary
is either a string containing the actual dictionary text, or the name of a file containing the dictionary. (The system can easily distinguish between them.) XML dictionaries are currently supported, and additional formats may be supported in the future. The query is expressed in “XPath 1.0” syntax (or a reasonable subset therof).The return value is a Node ID, an opaque integer identifier that is the handle of a node within the dictionary data. The value 0 is reserved to mean “query not found” and the value 1 indicates that the dictionary was not a valid syntax (or, if a file, could not be read). If more than one node within the dictionary matched the query, the node ID of the first match is returned, and
dict_next()
may be used to step to the next matching node.The version that takes a nodeID rather than a dictionary string simply interprets the query as being relative to the node specified by nodeID, as opposed to relative to the root of the dictionary.
All expensive operations (such as reading the dictionary from a file and the initial parsing of the dictionary) are performed only once, and subsequent lookups merely copy data and are thus inexpensive. The
dictionary
string is, therefore, used as a hash into a cached data structure holding the parsed dictionary database. Implementations may also cache individual node lookups or type conversions behind the scenes.int
dict_next
(int nodeID)
Return the node ID of the next node that matched the query that returned nodeID, or 0 if nodeID was the last matching node for its query.
int
dict_value
(int nodeID, string attribname, output
type
value)
Retrieves the named attribute of the given dictionary node, or the value of the node itself if
attribname
is the empty string""
. If the attribute is found, its value will be stored invalue
and 1 will be returned. If the requested attribute is not found on the node, or if the type ofvalue
does not appear to match that of the named node,value
will be unmodified and 0 will be returned.Type conversions are straightforward: anything may be retrieved as a string; to retrieve as an int or float, the value must parse as a single integer or floating point value; to retrieve as a point, vector, normal, color, or matrix (or any array), the value must parse as the correct number of values, separated by spaces and/or commas.
int
trace
(point pos, vector dir, ...)
Trace a ray from pos in the direction dir. The ray is traced immediately, and may incur significant expense compared to rays that might be traced incidentally to evaluating the
Ci
closure. Also, beware that this can be easily abused in such a way as to introduce viewdependence into shaders. The return value is 0 if the ray missed all geometry, 1 if it hit anything within the distance range.The following optional keyvalue arguments (see Section Function calls) can be passed:
"mindist",
float
The minimum hit distance (default: 0).
The units of the
"mindist"
and"maxdist"
are determined by the renderer and are sometimes defined by the dir vector, which can lead to unexpected behavior. So, generally, clearly written and portable shaders should pass a unit length (see Section Geometric functions) dir vector."mindist",
float
The maximum hit distance (default: infinite).
"shade",
int
Defines whether objects hit will be shaded (default: 0).
"traceset",
string
An optional named set of objects to ray trace (if preceded by a

character, it means to exclude that set).Information about the closest object hit by the ray may be retrieved using
getmessage("trace",...)
(see Section Renderer state and message passing).
The main purpose of this function is to allow shaders to “probe” nearby geometry, for example to apply a projected texture that can be blocked by geometry, apply more “wear” to exposed geometry, or make other ambient occlusionlike effects.
7.13. Miscellaneous#
int
arraylength
(
type
A[])
Returns the length of the referenced array, which may be of any type.
void
exit
()
Exits the shader without further execution. Within the main body of a shader, this is equivalent to calling
return
, but inside a function,exit()
will exit the entire shader, whereasreturn
would only exit the enclosing function.