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| Context(s) | shading |
vector reflectlight(float bias, float max_contrib, ...)
bias is typically a small number (for example 0.005) used to help
eliminate self-reflection. If bias is less than 0, the default
ray tracing bias specified with the vm_raybias setting will be used
instead.
max_contrib tells the renderer how much the reflected light will contribute to the final color of the pixel. This is typically the maximum of the reflection component of a lighting model. This has no effect on the resultant color. This value should typically be less than 1.
vector reflectlight(vector P, vector D, float bias, float max_contrib, ...)
A general form which takes a position P and a direction D.
vector reflectlight(vector P, vector N, vector I, float bias, float max_contrib, ...)
A general form which takes a position P, direction D, and incident angle I and returns the reflection vector.
Area sampling options
For area sampling, you must specify both the angle and sample variadic parameters. For example:
surface blurry_mirror(float angle = 3; int samples = 16; float bias=0.05) { Cf = reflectlight(bias, 1, "angle", angle, "samples", samples); }
Ray options
Tip
When you specify a texture, such as with the "environment" keyword,
you can also use the image filtering keyword arguments. See environment
for a listing of the image filter keyword arguments.
"scope",
string
A list of objects which can be hit by the rays. When specified, scope overrides the default scope that would have been selected for the given raystyle. The "scope:default" value will cause the scope argument to use the default scope for the current context - as if the argument were not specified.
Allows an override of the scope for ray-intersections.
A special scope argument, scope:self, will match the currently
shading object.
"maxdist",
float
=-1
The maximum distance to search for objects. This can be used to limit the search of objects to nearby objects only. If the maxdist given is negative, then it will act as if there is no maximum distance.
Allows an override of the maximum distance the ray can travel when testing for intersections. Some functions (such as fastshadow) have the maximum distance implicitly defined (by the length of the ray) and should probably avoid using this option. However, this option can be used effectively when computing reflections, global illumination, refraction etc.
"variancevar",
string
The name of a VEX export variable to use for variance anti-aliasing. The renderer compares the value with adjacent micropolygons in micropolygon rendering to decide what shading points need additional samples (using vm_variance property as a threshold). If more samples are required, the algorithm takes samples up to the specified maximum ray samples.
This variable must be imported from the hit surface, so it must be in the list of imported names (see "importing information back from the ray" below). If the named variable is not imported, this option will be ignored.
Variance antialiasing puts more samples in areas of the image with high variance, for example a sharp shadow edge. It is only used when vm_dorayvariance is enabled. Otherwise, only the min ray samples (or an explicitly supplied "samples" value) are used for antialiasing of the gather loop.
Overrides the global variance control (mantra’s -v option) which is used to determine anti-aliasing quality of ray tracing. For more information please refer to the documentation on mantra.
"angle",
float
=0
The distribution angle (specified in radians). For gather(), rays will be distributed over this angle. For trace(), the angle is used to indicate the rate at which the filter width should increase with increasing intersection distance. Larger angles will cause farther hit surfaces to use larger derivatives, leading to improved texturing and displacement performance.
To be effective, the samples parameter should also be specified.
"samples",
int|float
=1
How many samples should be sent out to filter rays. For the irradiance and occlusion functions, specifying a samples parameter will override the default irradiance sampling.
"environment",
string
If the ray sent out to the scene misses everything, then it’s possible to specify an environment map to evaluate.
Using the ray’s direction, the environment map specified will be evaluated and the resulting color will be returned. Most likely, it will be necessary to specify a transform space for the environment map evaluations.
In the case of refractlight and trace the Of and Af variables will be set to 0 regardless of the background color specified. the resulting color.
When an environment map is specified, the filtering options from texture() are also supported.
"envobject",
string
If an environment map is used, the orientation of the environment map can be specified by transforming the ray into the space of another object, light or fog object in the scene. In Houdini, null objects can be used to specify the orientation. For example:
Cf = R*reflectlight(bias, max(R), "environment", "map.rat", "envobject", "null_object_name");
"envlight",
string
If an environment map is used, the orientation of the environment map can be specified by transforming the ray into the space of a light in the scene.
"envtint",
vector
If an environment map is used, tint it with this color.
"background",
vector
If a ray misses all objects, use this as the background color of the scene. In the case of refractlight and trace the Of and Af variables will be set to 0 regardless of the background color specified.
"distribution",
string
Functions: irradiance, occlusion
Distribution for computing irradiance. The default is to use
a cosine distribution (diffuse illumination). The possible
values for the style are "nonweighted" for uniform sampling
or "cosine" for cosine weighted sampling.
Image filtering options
Examples of specifying filter parameters:
colormap(map, u, v, "smode", "decal", "tmode", "repeat", "border", {.1,1,1}); colormap(map, u, v, "mode", "clamp", "width", 1.3); colormap(map, u, v, "filter", "gauss", "width", 1.3, "mode", "repeat");
If the texture is a deep .rat file, you can use the "channel" keyword argument
to specify a channel in the file:
string channelname = "N"; cf = colormap(map, u, v, "channel", channelname);
"wrap",
string
="repeat"
repeat or periodic
The image map will repeat outside the range 0 to 1. Basically, the integer component of the texture coordinate is ignored. This is the default.
clamp or edge or streak
The texture coordinates will be clamped to the range 0 to 1. This causes evaluations outside the range to evaluate to the color at the closest edge of the image (the border pixels are streaked outside the range).
black or decal or color
Coordinates outside the range 0 to 1 will evaluate to the border color (rather than a color in the image). The border color is black (i.e. 0) by default.
"uwrap",
string
(AKA swrap)
Specifies the behavior when the u coordinate is outside
the range 0 to 1. The values are the same as with wrap.
"vwrap",
string
(AKA twrap)
Specifies the behavior when the v coordinate is outside
the range 0 to 1. The values are the same as with wrap.
"border",
float|vector|vector4
=0
Specifies the border color when Black/Decal/Color wrapping is used.
"channel",
Specifies the color channel for textures that have multiple color
planes (for example, diffuse_indirect or N).
For ptex images, this specifies the index of the first channel
(for example, 0 or 4).
"blur",
float
Blurs in x and y directions. Blur is measured as a percentage
of the image size - so a blur of 0.1 will blur 10% of the image
width. Use xblur and yblur if you need different blur
amounts in either dimension.
"xblur",
(AKA ublur, sblur)
Blur amount in the x image direction.
"yblur",
(AKA vblur, tblur)
Blur amount in the y image direction.
"pixelblur",
float
Blurs the texture by a floating point number of pixels.
Cf = texture("map.rat", ss, tt, "pixelblur", 2.0);
"xpixelblur",
float
Blurs the texture by a floating point number of pixels in the X direction.
"ypixelblur",
float
Blurs the texture by a floating point number of pixels in the Y direction.
"filter",
string
="box"
Specifies the type of anti-aliasing filter to be used for evaluation. The following argument should be a string specifying one of:
point
Point sampling (i.e. no filtering)
box
Box filter (default)
gauss
Gaussian filter
bartlett
Bartlett/Triangular filter
sinc
Sinc sharpening filter
hanning
Hanning filter
blackman
Blackman filter
catrom
Catmull-Rom filter
"xfilter",
string
(AKA ufilter, sfilter)
Specifies the filter for the X direction. The filters are
the same as with filter.
"yfilter",
string
(AKA vfilter, tfilter)
Specifies the filter for the Y direction. The filters are
the same as with filter.
"width",
float
=1.0
Filter width in both X and Y directions.
"xwidth",
float
(AKA uwidth, swidth)
Filter width in the X direction.
"ywidth",
float
(AKA vwidth, twidth)
Filter width in the Y direction.
"zwidth",
float
Filter width in the Z direction (for shadow maps). This is measured in world space units, unlike the other width arguments.
"extrapolate",
int
whether to use derivative extrapolation when computing anti-aliasing information. Extrapolation of derivatives is on by default. The argument should be either 0 or 1.
"lerp",
int
Specifies whether RAT files should interpolate between different MIP levels. By default, this is turned off. Turning interpolation on will help remove discontinuities when different MIP levels of a .rat file are accessed. However, the results of texture evaluation will be slightly softer (i.e. blurrier) and will take more time.
There are three possible values for this argument.
0
Disable MIP map interpolation (fastest).
1
Approximate MIP map interpolation (fast).
2
High Quality MIP map interpolation (slower but highest quality).
"depthinterp",
string
Specifies the depth interpolation mode for deep shadow maps, to control the opacity value that will be returned when the map is sampled between two z-records.
The argument must be a string.
discrete
(default) Return the first z-record before the sample point.
linear
Linearly interpolate the opacities of the z-records before and after the sample point.
See deep shadow maps for more on the difference between the two modes.
"beerlambert",
int
When evaluating volumetric deep shadow maps, this will enable Beer-Lambert interpolation of opacity. Beer-Lambert is more a accurate but more expensive form of interpolation.
The argument should be either 0 or 1.
"srccolorspace",
string
Specifies the color space in which the texture is stored. When texture values are accessed, they will be translated from this space into linear space for rendering if needed.
auto
(default) Determine the source color space based on the file. Currently, this will assume sRGB color space for 8-bit textures and linear for all other textures.
linear
Transform to linear space. This currently only affects 8-bit textures, since all others are assumed to be already in linear space. Use this option to force linear interpretation of textures used for bump or displacement maps.
"face",
When using a Ptex texture map, the face argument is used to
specify the face for ptexture lookup.
"ptexorient",
int
When using Ptex textures, the implicit texture coordinates on
polygons are used as the interpolants for texture lookup (combined
with the face). However, different software may have different
beliefs about winding and orientation. This keyword argument
allows you to control the interpretation of orientation for Houdini
polygons. The ptexorient expects an integer argument which is
composed of a bit-field
For example, a value of 6 (0×4|0×2) is equivalent to calling
texture(map, 1-t, s) instead of texture(map, s, t).
The default ptexorient is 0, which works correctly with the
examples found at https://ptex.us.
Examples
surface mirror(vector refl_color=1; float bias=.005) { Cf = refl_color * reflectlight(bias, max(refl_color)); }
| See also | |
| surface |