GLCOPYCONVOLUTIONFIL(3G)

NAME
glCopyConvolutionFilter2D - copy pixels into a two-dimensional convolution filter

C SPECIFICATION

void glCopyConvolutionFilter2D(GLenum target, GLenum internalformat, GLint x, GLint y, GLsizei width, GLsizei height);

PARAMETERS

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, y
    The window space coordinates of the lower-left coordinate of the pixel array to copy.

width
    The width of the pixel array to copy.

height
    The height of the pixel array to copy.

DESCRIPTION

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().

NOTES

glCopyConvolutionFilter2D is present only if ARB_imaging is returned when glGetString() is called with an argument of GL_EXTENSIONS.

ERRORS

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().

ASSOCIATED GETS

glGetConvolutionParameter(), glGetConvolutionFilter()

SEE ALSO

glConvolutionFilter2D(), glConvolutionParameter(), glPixelTransfer()

COPYRIGHT

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/.