glCopyConvolutionFilter2D — copy pixels into a two-dimensional convolution filter
void glCopyConvolutionFilter2D( | GLenum | target, |
| GLenum | internalformat, | |
| GLint | x, | |
| GLint | y, | |
| GLsizei | width, | |
| GLsizei | height); |
target
Must be GL_CONVOLUTION_2D.
internalformat
The internal format of the convolution filter kernel.
The allowable values are
GL_ALPHA,
GL_ALPHA4,
GL_ALPHA8,
GL_ALPHA12,
GL_ALPHA16,
GL_LUMINANCE,
GL_LUMINANCE4,
GL_LUMINANCE8,
GL_LUMINANCE12,
GL_LUMINANCE16,
GL_LUMINANCE_ALPHA,
GL_LUMINANCE4_ALPHA4,
GL_LUMINANCE6_ALPHA2,
GL_LUMINANCE8_ALPHA8,
GL_LUMINANCE12_ALPHA4,
GL_LUMINANCE12_ALPHA12,
GL_LUMINANCE16_ALPHA16,
GL_INTENSITY,
GL_INTENSITY4,
GL_INTENSITY8,
GL_INTENSITY12,
GL_INTENSITY16,
GL_R3_G3_B2,
GL_RGB,
GL_RGB4,
GL_RGB5,
GL_RGB8,
GL_RGB10,
GL_RGB12,
GL_RGB16,
GL_RGBA,
GL_RGBA2,
GL_RGBA4,
GL_RGB5_A1,
GL_RGBA8,
GL_RGB10_A2,
GL_RGBA12, or
GL_RGBA16.
x, yThe window space coordinates of the lower-left coordinate of the pixel array to copy.
widthThe width of the pixel array to copy.
heightThe height of the pixel array to copy.
glCopyConvolutionFilter2D defines a two-dimensional convolution filter kernel with pixels
from the current GL_READ_BUFFER (rather than from main memory,
as is the case for glConvolutionFilter2D).
The screen-aligned pixel rectangle with lower-left corner at (x,\ y),
width width and height height
is used to define the convolution filter. If any pixels within this
region are
outside the window that is associated with the GL context, the
values obtained for those pixels are undefined.
The pixels in the rectangle are processed
exactly as if glReadPixels had been called with format
set to RGBA, but the process stops just before final conversion.
The R, G, B, and A components of each pixel are next scaled by the four
2D GL_CONVOLUTION_FILTER_SCALE parameters and biased by the
four 2D GL_CONVOLUTION_FILTER_BIAS parameters.
(The scale and bias parameters are set by glConvolutionParameter
using the GL_CONVOLUTION_2D target and the names
GL_CONVOLUTION_FILTER_SCALE and GL_CONVOLUTION_FILTER_BIAS.
The parameters themselves are vectors of four values that are applied to red,
green, blue, and alpha, in that order.)
The R, G, B, and A values are not clamped to [0,1] at any time during this
process.
Each pixel is then converted to the internal format specified by
internalformat.
This conversion simply maps the component values of the pixel (R, G, B,
and A) to the values included in the internal format (red, green, blue,
alpha, luminance, and intensity). The mapping is as follows:
| Internal Format | Red | Green | Blue | Alpha | Luminance | Intensity |
|---|---|---|---|---|---|---|
GL_ALPHA
| A | |||||
GL_LUMINANCE
| R | |||||
GL_LUMINANCE_ALPHA
| A | R | ||||
GL_INTENSITY
| R | |||||
GL_RGB
| R | G | B | |||
GL_RGBA
| R | G | B | A |
The red, green, blue, alpha, luminance, and/or intensity components of the resulting pixels are stored in floating-point rather than integer format.
Pixel ordering is such that lower x screen coordinates correspond to lower i filter image coordinates, and lower y screen coordinates correspond to lower j filter image coordinates.
Note that after a convolution is performed, the resulting color
components are also scaled by their corresponding
GL_POST_CONVOLUTION_c_SCALE parameters and biased by their
corresponding GL_POST_CONVOLUTION_c_BIAS parameters (where
c takes on the values RED, GREEN, BLUE, and
ALPHA).
These parameters are set by glPixelTransfer.
glCopyConvolutionFilter2D is present only if ARB_imaging is returned when glGetString
is called with an argument of GL_EXTENSIONS.
GL_INVALID_ENUM is generated if target is not
GL_CONVOLUTION_2D.
GL_INVALID_ENUM is generated if internalformat is not one of the
allowable values.
GL_INVALID_VALUE is generated if width is less than zero or greater
than the maximum supported value.
This value may be queried with glGetConvolutionParameter
using target GL_CONVOLUTION_2D and name
GL_MAX_CONVOLUTION_WIDTH.
GL_INVALID_VALUE is generated if height is less than zero or greater
than the maximum supported value.
This value may be queried with glGetConvolutionParameter
using target GL_CONVOLUTION_2D and name
GL_MAX_CONVOLUTION_HEIGHT.
GL_INVALID_OPERATION is generated if glCopyConvolutionFilter2D is executed
between the execution of glBegin and the corresponding
execution of glEnd.
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.