HP c3700 - Workstation, Reference Manual, Page: 334 / 486

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glPixelTransfer
Chapter 14
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Each of the four color components is multiplied by a scale factor, then added to a bias
factor. That is, the red component is multiplied by GL_RED_SCALE, then added to
GL_RED_BIAS; the green component is multiplied by GL_GREEN_SCALE, then added
to GL_GREEN_BIAS; the blue component is multiplied by GL_BLUE_SCALE, then
added to GL_BLUE_BIAS; and the alpha component is multiplied by
GL_ALPHA_SCALE, then added to GL_ALPHA_BIAS. After all four color components
are scaled and biased, each is clamped to the range [0, 1]. All color, scale, and bias values
are specified with glPixelTransfer.
If GL_MAP_COLOR is true, each color component is scaled by the size of the
corresponding color-to-color map, then replaced by the contents of that map indexed by
the scaled component. That is, the red component is scaled by
GL_PIXEL_MAP_R_TO_R_SIZE, then replaced by the contents of
GL_PIXEL_MAP_R_TO_R indexed by itself. The green component is scaled by
GL_PIXEL_MAP_G_TO_G_SIZE, then replaced by the contents of
GL_PIXEL_MAP_G_TO_G indexed by itself. The blue component is scaled by
GL_PIXEL_MAP_B_TO_B_SIZE, then replaced by the contents of
GL_PIXEL_MAP_B_TO_B indexed by itself. And the alpha component is scaled by
GL_PIXEL_MAP_A_TO_A_SIZE, then replaced by the contents of
GL_PIXEL_MAP_A_TO_A indexed by itself. All components taken from the maps are
then clamped to the range [0, 1]. GL_MAP_COLOR is specified with glPixelTransfer. The
contents of the various maps are specified with glPixelMap.
Color index
Each color index is shifted left by GL_INDEX_SHIFT bits; any bits beyond the number
of fraction bits carried by the fixed-point index are filled with zeros. If
GL_INDEX_SHIFT is negative, the shift is to the right, again zero filled. Then
GL_INDEX_OFFSET is added to the index. GL_INDEX_SHIFT and
GL_INDEX_OFFSET are specified with glPixelTransfer.
From this point, operation diverges depending on the required format of the resulting
pixels. If the resulting pixels are to be written to a color index buffer, or if they are being
read back to client memory in GL_COLOR_INDEX format, the pixels continue to be
treated as indices. If GL_MAP_COLOR is true, each index is masked by 2
n
-1, where n is
GL_PIXEL_MAP_I_TO_I_SIZE, then replaced by the contents of
GL_PIXEL_MAP_I_TO_I indexed by the masked value. GL_MAP_COLOR is specified
with glPixelTransfer. The contents of the index map is specified with glPixelMap.
If the resulting pixels are to be written to an RGBA color buffer, or if they are read back
to client memory in a format other than GL_COLOR_INDEX, the pixels are converted
from indices to colors by referencing the four maps GL_PIXEL_MAP_I_TO_R,
GL_PIXEL_MAP_I_TO_G, GL_PIXEL_MAP_I_TO_B, and GL_PIXEL_MAP_I_TO_A.
Before being de-referenced, the index is masked by 2
n
- 1, where n is
GL_PIXEL_MAP_I_TO_R_SIZE for the red map, GL_PIXEL_MAP_I_TO_G_SIZE for
the green map, GL_PIXEL_MAP_I_TO_B_SIZE for the blue map, and
GL_PIXEL_MAP_I_TO_A_SIZE for the alpha map. All components taken from the maps
are then clamped to the range [0, 1]. The contents of the four maps is specified with
glPixelMap.
Depth
Each depth value is multiplied by GL_DEPTH_SCALE, added to GL_DEPTH_BIAS,
then clamped to the range [0, 1].
Stencil