GLfloat param )
void GLAPIENTRY glPixelTransferi( GLenum pname,
GLint param )
PARAMETERS
pname Specifies the symbolic name of the pixel transfer parameter to be
set. Must be one of the following: 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.
param Specifies the value that pname 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 commands. Addi‐
tionally, if the GL_ARB_imaging subset is supported, 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 glTexSubImage3D).
Pixel transfer operations happen in the same order, and in the same man‐
ner, regardless of the command that resulted in the pixel operation.
Pixel storage modes (see glPixelStore) control the unpacking of pixels
being read from client memory, and the packing of pixels being written
back into client memory.
Pixel transfer operations handle four fundamental pixel types: color,
color index, depth, and stencil. Color pixels consist of four floating-
point values with unspecified mantissa and exponent sizes, scaled such
that 0 represents zero intensity and 1 represents full intensity. Color
indices comprise a single fixed-point value, with unspecified precision
to the right of the binary point. Depth pixels comprise a single float‐
nent 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 re‐
placed 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 re‐
placed by the contents of GL_PIXEL_MAP_B_TO_B indexed by it‐
self. 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 con‐
tents 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 tran‐
formation by the color matrix. That is, the red component
is multiplied by GL_POST_COLOR_MATRIX_RED_SCALE, then added
to GL_POST_COLOR_MATRIX_RED_BIAS; the green component is
multiplied by GL_POST_COLOR_MATRIX_GREEN_SCALE, then added
to GL_POST_COLOR_MATRIX_GREEN_BIAS; the blue component is
multiplied by GL_POST_COLOR_MATRIX_BLUE_SCALE, then added to
GL_POST_COLOR_MATRIX_BLUE_BIAS; and the alpha component is
multiplied by GL_POST_COLOR_MATRIX_ALPHA_SCALE, then added
to GL_POST_COLOR_MATRIX_ALPHA_BIAS. After all four color
components are scaled and biased, each is clamped to the
range [0,1].
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 component is multi‐
plied by GL_POST_CONVOLUTION_GREEN_SCALE, then added to
GL_POST_CONVOLUTION_GREEN_BIAS; the blue component is multi‐
plied 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 compo‐
nents are scaled and biased, each is clamped to the range
[0,1].
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 con‐
tents 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 for‐
mat 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 by 2n−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 Each index is shifted GL_INDEX_SHIFT bits just 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.
─────────────────────────────────────────────────────────────────────────
pname Type Initial Value Valid Range
─────────────────────────────────────────────────────────────────────────
GL_MAP_COLOR boolean false true/false
GL_MAP_STENCIL boolean false true/false
GL_INDEX_SHIFT integer 0 (-∞,∞)
GL_INDEX_OFFSET integer 0 (-∞,∞)
GL_RED_SCALE float 1 (-∞,∞)
GL_GREEN_SCALE float 1 (-∞,∞)
GL_BLUE_SCALE float 1 (-∞,∞)
GL_ALPHA_SCALE float 1 (-∞,∞)
GL_DEPTH_SCALE float 1 (-∞,∞)
GL_RED_BIAS float 0 (-∞,∞)
GL_GREEN_BIAS float 0 (-∞,∞)
GL_BLUE_BIAS float 0 (-∞,∞)
GL_ALPHA_BIAS float 0 (-∞,∞)
GL_DEPTH_BIAS float 0 (-∞,∞)
GL_POST_COLOR_MATRIX_RED_SCALE float 1 (-∞,∞)
GL_POST_COLOR_MATRIX_GREEN_SCALE float 1 (-∞,∞)
GL_POST_CONVOLUTION_ALPHA_BIAS float 0 (-∞,∞)
─────────────────────────────────────────────────────────────────────────
glPixelTransferf can be used to set any pixel transfer parameter. If
the parameter type is boolean, 0 implies false and any other value im‐
plies true. If pname is an integer parameter, param is rounded to the
nearest integer.
Likewise, glPixelTransferi can be used to set any of the pixel transfer
parameters. Boolean parameters are set to false if param is 0 and to
true otherwise. param is converted to floating point before being as‐
signed to real-valued parameters.
NOTES
If a glColorTable, glColorSubTable, glConvolutionFilter1D,
glConvolutionFilter2D, glCopyPixels, glCopyTexImage1D, glCopyTexImage2D,
glCopyTexSubImage1D, glCopyTexSubImage2D, glCopyTexSubImage3D,
glDrawPixels, glReadPixels, glSeparableFilter2D, glTexImage1D,
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 different from
the settings when the command was compiled into the display list.
ERRORS
GL_INVALID_ENUM is generated if pname is not an accepted value.
GL_INVALID_OPERATION is generated if glPixelTransfer is executed between
the execution of glBegin and the corresponding 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
glDrawPixels, glNewList, glPixelMap, glPixelStore, glPixelZoom,
glReadPixels, glTexImage1D, glTexImage2D, glTexImage3D, glTexSubImage1D,
glTexSubImage2D, glTexSubImage3D
GLPIXELTRANSFER(3G)
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