DESCRIPTION
glCopyConvolutionFilter1D defines a one-dimensional convolution filter kernel with pixels from the current
GL_READ_BUFFER (rather than from main memory, as is the case for
glConvolutionFilter1D).
The screen-aligned pixel rectangle with lower-left corner at (
x,
y), width
width and height 1 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 1D
GL_CONVOLUTION_FILTER_SCALE parameters and biased by the four 1D
GL_CONVOLUTION_FILTER_BIAS parameters. (The scale and bias parameters are set by
glConvolutionParameter using the
GL_CONVOLUTION_1D 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.
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.