GLCOPYCONVOLUTIONFILTER2D(3G) GLCOPYCONVOLUTIONFILTER2D(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 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 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 (red,
green, blue, alpha, luminance, and intensity). The mapping is as follows:
Internal Format Channel mapping
GL_ALPHA A=Alpha
GL_LUMINANCE R=Luminance
GL_LUMINANCE_ALPHA A=Alpha, R=Luminance
GL_INTENSITY R=Intensity
GL_RGB R=Red, G=Green, B=Blue
GL_RGBA R=Red, G=Green, B=Blue, A=Alpha
The red, green, blue, alpha, luminance, and/or intensity components of the resulting pixels are
stored in floating-point rather than integer
Pixel ordering is such that lower x screen coordinates correspond to lower i filter image coordi-nates, coordinates,
nates, 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 GL_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(3G), glConvolutionParameter(3G), glPixelTransfer(3G)
GLCOPYCONVOLUTIONFILTER2D(3G)
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