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float filterstep(float edge, float x, ...)
float filterstep(float edge, float x0, float x1, ...)
Returns the anti-aliased weight of the step function. The
step function returns 0 if x is less than edge and 1 if x is greater
than edge. filterstep returns a fraction representing the
filtered area under the step function. Filtering is computed using
derivatives Du() and Dv() which are only non-zero in shading and COP
contexts, so filterstep will not perform filtering in other contexts.
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
f = filterstep(0.5, s+t, "filter", "gauss", "width", 2);
The filterstep(float edge, x, ...) form is roughly equivalent to:
f = filterstep(edge, x, x + abs(Du(x) + Dv(x)));
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