- set pixel transfer modes
C SPECIFICATION
PARAMETERS
_param1 Specifies the symbolic name of the pixel transfer
parameter to be set. Must be one of the follow-
ing: GL_MAP_COLOR, GL_MAP_STENCIL,
GL_INDEX_SHIFT, GL_INDEX_OFFSET, GL_RED_SCALE,
GL_RED_BIAS, GL_GREEN_SCALE, GL_GREEN_BIAS,
GL_BLUE_SCALE, GL_BLUE_BIAS, GL_ALPHA_SCALE,
GL_ALPHA_BIAS, GL_DEPTH_SCALE, or GL_DEPTH_BIAS.
Additionally, if the GL_ARB_imaging extension is
supported, the following symbolic names are
accepted: GL_POST_COLOR_MATRIX_RED_SCALE,
GL_POST_COLOR_MATRIX_GREEN_SCALE,
GL_POST_COLOR_MATRIX_BLUE_SCALE,
GL_POST_COLOR_MATRIX_ALPHA_SCALE,
GL_POST_COLOR_MATRIX_RED_BIAS,
GL_POST_COLOR_MATRIX_GREEN_BIAS,
GL_POST_COLOR_MATRIX_BLUE_BIAS,
GL_POST_COLOR_MATRIX_ALPHA_BIAS,
GL_POST_CONVOLUTION_RED_SCALE,
GL_POST_CONVOLUTION_GREEN_SCALE,
GL_POST_CONVOLUTION_BLUE_SCALE,
GL_POST_CONVOLUTION_ALPHA_SCALE,
GL_POST_CONVOLUTION_RED_BIAS,
GL_POST_CONVOLUTION_GREEN_BIAS,
GL_POST_CONVOLUTION_BLUE_BIAS, and
GL_POST_CONVOLUTION_ALPHA_BIAS.
_param2 Specifies the value that _param1 is set to.
DESCRIPTION
glPixelTransfer sets pixel transfer modes that affect the
operation of subsequent glCopyPixels, glCopyTexImage1D,
glCopyTexImage2D, glCopyTexSubImage1D,
glCopyTexSubImage2D, glCopyTexSubImage3D, glDrawPixels,
glReadPixels, glTexImage1D, glTexImage2D, glTexImage3D,
glTexSubImage1D, glTexSubImage2D, and glTexSubImage3D com-
mands. Additionally, if the GL_ARB_imaging subset is sup-
ported, the routines glColorTable, glColorSubTable,
glConvolutionFilter1D, glConvolutionFilter2D, glHistogram,
glMinmax, and glSeparableFilter2D are also affected. The
algorithms that are specified by pixel transfer modes
operate on pixels after they are read from the frame
buffer (glCopyPixels glCopyTexImage1D, glCopyTexImage2D,
glCopyTexSubImage1D, glCopyTexSubImage2D,
glCopyTexSubImage3D, and glReadPixels), or unpacked from
client memory (glDrawPixels, glTexImage1D, glTexImage2D,
glTexImage3D, glTexSubImage1D, glTexSubImage2D, and
pixels comprise a single floating-point value, with
unspecified mantissa and exponent sizes, scaled such that
0.0 represents the minimum depth buffer value, and 1.0
represents the maximum depth buffer value. Finally, sten-
cil pixels comprise a single fixed-point value, with
unspecified precision to the right of the binary point.
The pixel transfer operations performed on the four basic
pixel types are as follows:
Color Each of the four color components is multi-
plied by a scale factor, then added to a bias
factor. That is, the red component is multi-
plied 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 multi-
plied by GL_BLUE_SCALE, then added to
GL_BLUE_BIAS; and the alpha component is mul-
tiplied by GL_ALPHA_SCALE, then added to
GL_ALPHA_BIAS. After all four color compo-
nents 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 con-
tents of that map indexed by the scaled compo-
nent. 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.
If the GL_ARB_imaging extension is supported,
each of the four color components may be
scaled and biased after tranformation by the
color matrix. That is, the red component is
Similiarly, if the GL_ARB_imaging extension is
supported, each of the four color components
may be scaled and biased after processing by
the enabled convolution filter. That is, the
red component is multiplied by
GL_POST_CONVOLUTION_RED_SCALE, then added to
GL_POST_CONVOLUTION_RED_BIAS; the green compo-
nent is multiplied by
GL_POST_CONVOLUTION_GREEN_SCALE, then added to
GL_POST_CONVOLUTION_GREEN_BIAS; the blue com-
ponent is multiplied by
GL_POST_CONVOLUTION_BLUE_SCALE, then added to
GL_POST_CONVOLUTION_BLUE_BIAS; and the alpha
component is multiplied by
GL_POST_CONVOLUTION_ALPHA_SCALE, then added to
GL_POST_CONVOLUTION_ALPHA_BIAS. After all
four color components are scaled and biased,
each is clamped to the range [0,1].
Color index Each color index is shifted left by
GL_INDEX_SHIFT bits; any bits beyond the num-
ber 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 speci-
fied with
glPixelTransfer.
From this point, operation diverges depending
on the required 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 , the
pixels continue to be treated as indices. If
GL_MAP_COLOR is true, each index is masked by
2n-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 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 dereferenced, the index is masked
as a color index is, then added to
GL_INDEX_OFFSET. If GL_MAP_STENCIL is true,
each index is masked by 2n-1, where n is
GL_PIXEL_MAP_S_TO_S_SIZE, then replaced by the
contents of GL_PIXEL_MAP_S_TO_S indexed by the
masked value.
The following table gives the type, initial value, and
range of valid values for each of the pixel transfer
parameters that are set with glPixelTransfer.
-------------------------------------------------------------------------
_param1 Type Initial Value Valid Range
-------------------------------------------------------------------------
GL_MAP_COLOR boolean false true/false
GL_MAP_STENCIL boolean false true/false
GL_INDEX_SHIFT integer 0 (-oo,oo)
GL_INDEX_OFFSET integer 0 (-oo,oo)
GL_RED_SCALE float 1 (-oo,oo)
GL_GREEN_SCALE float 1 (-oo,oo)
GL_BLUE_SCALE float 1 (-oo,oo)
GL_ALPHA_SCALE float 1 (-oo,oo)
GL_DEPTH_SCALE float 1 (-oo,oo)
GL_RED_BIAS float 0 (-oo,oo)
GL_GREEN_BIAS float 0 (-oo,oo)
GL_BLUE_BIAS float 0 (-oo,oo)
GL_ALPHA_BIAS float 0 (-oo,oo)
GL_DEPTH_BIAS float 0 (-oo,oo)
GL_POST_COLOR_MATRIX_RED_SCALE float 1 (-oo,oo)
GL_POST_COLOR_MATRIX_GREEN_SCALE float 1 (-oo,oo)
GL_POST_COLOR_MATRIX_BLUE_SCALE float 1 (-oo,oo)
GL_POST_COLOR_MATRIX_ALPHA_SCALE float 1 (-oo,oo)
GL_POST_COLOR_MATRIX_RED_BIAS float 0 (-oo,oo)
GL_POST_COLOR_MATRIX_GREEN_BIAS float 0 (-oo,oo)
GL_POST_COLOR_MATRIX_BLUE_BIAS float 0 (-oo,oo)
GL_POST_COLOR_MATRIX_ALPHA_BIAS float 0 (-oo,oo)
GL_POST_CONVOLUTION_RED_SCALE float 1 (-oo,oo)
GL_POST_CONVOLUTION_GREEN_SCALE float 1 (-oo,oo)
GL_POST_CONVOLUTION_BLUE_SCALE float 1 (-oo,oo)
GL_POST_CONVOLUTION_ALPHA_SCALE float 1 (-oo,oo)
GL_POST_CONVOLUTION_RED_BIAS float 0 (-oo,oo)
GL_POST_CONVOLUTION_GREEN_BIAS float 0 (-oo,oo)
GL_POST_CONVOLUTION_BLUE_BIAS float 0 (-oo,oo)
GL_POST_CONVOLUTION_ALPHA_BIAS float 0 (-oo,oo)
-------------------------------------------------------------------------
glPixelTransferf can be used to set any pixel transfer
parameter. If the parameter type is boolean, 0 implies
false and any other value implies true. If _param1 is an
integer parameter, _param2 is rounded to the nearest inte-
glTexImage2D, glTexImage3D, glTexSubImage1D,
glTexSubImage2D, or glTexSubImage3D. command is placed in
a display list (see glNewList and glCallList), the pixel
transfer mode settings in effect when the display list is
executed are the ones that are used. They may be differ-
ent from the settings when the command was compiled into
the display list.
ERRORS
GL_INVALID_ENUM is generated if _param1 is not an accepted
value.
GL_INVALID_OPERATION is generated if glPixelTransfer is
executed between the execution of glBegin and the corre-
sponding execution of glEnd.
ASSOCIATED GETS
glGet with argument GL_MAP_COLOR
glGet with argument GL_MAP_STENCIL
glGet with argument GL_INDEX_SHIFT
glGet with argument GL_INDEX_OFFSET
glGet with argument GL_RED_SCALE
glGet with argument GL_RED_BIAS
glGet with argument GL_GREEN_SCALE
glGet with argument GL_GREEN_BIAS
glGet with argument GL_BLUE_SCALE
glGet with argument GL_BLUE_BIAS
glGet with argument GL_ALPHA_SCALE
glGet with argument GL_ALPHA_BIAS
glGet with argument GL_DEPTH_SCALE
glGet with argument GL_DEPTH_BIAS
glGet with argument GL_POST_COLOR_MATRIX_RED_SCALE
glGet with argument GL_POST_COLOR_MATRIX_RED_BIAS
glGet with argument GL_POST_COLOR_MATRIX_GREEN_SCALE
glGet with argument GL_POST_COLOR_MATRIX_GREEN_BIAS
glGet with argument GL_POST_COLOR_MATRIX_BLUE_SCALE
glGet with argument GL_POST_COLOR_MATRIX_BLUE_BIAS
glGet with argument GL_POST_COLOR_MATRIX_ALPHA_SCALE
glGet with argument GL_POST_COLOR_MATRIX_ALPHA_BIAS
glGet with argument GL_POST_CONVOLUTION_RED_SCALE
glGet with argument GL_POST_CONVOLUTION_RED_BIAS
glGet with argument GL_POST_CONVOLUTION_GREEN_SCALE
glGet with argument GL_POST_CONVOLUTION_GREEN_BIAS
glGet with argument GL_POST_CONVOLUTION_BLUE_SCALE
glGet with argument GL_POST_CONVOLUTION_BLUE_BIAS
glGet with argument GL_POST_CONVOLUTION_ALPHA_SCALE
glGet with argument GL_POST_CONVOLUTION_ALPHA_BIAS
SEE ALSO
glCallList, glColorTable, glColorSubTable,
glConvolutionFilter1D, glConvolutionFilter2D,
glCopyPixels, glCopyTexImage1D, glCopyTexImage2D,