glCopyConvolutionFilter2D
GLCOPYCONVOLUTIONFILTER2D(3G) GLCOPYCONVOLUTIONFILTER2D(3G)
NAME
glCopyConvolutionFilter2D - copy pixels into a two-dimensional convo-
lution 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 coordi-
nate 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 fil-
ter. 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 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
Pixel ordering is such that lower x screen coordinates correspond to
lower i filter image coordinates, and lower y screen coordinates cor-
respond to lower j filter image coordinates.
Note that after a convolution is performed, the resulting color compo-
nents are also scaled by their corresponding
GL_POST_CONVOLUTION_c_SCALE parameters and biased by their correspond-
ing 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 exe-
cuted 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)
