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GLPIXELTRANSFER(3G) GLPIXELTRANSFER(3G)
NAME
glPixelTransferf, glPixelTransferi - set pixel transfer modes
C SPECIFICATION
void glPixelTransferf( GLenum pname,
GLfloat param )
void 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. Additionally, if the GL_ARB_imaging subset is sup-ported, supported,
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 glTexSubImage3D). Pixel transfer operations hap-pen happen
pen in the same order, and in the same manner, 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 sten-cil. stencil.
cil. 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 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, stencil pixels comprise a single fixed-point value, with unspecified preci-sion precision
sion 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 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 com-ponent. component.
ponent. 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
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 compo-nents components
nents 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 multiplied by
GL_POST_CONVOLUTION_GREEN_SCALE, then added to GL_POST_CONVOLUTION_GREEN_BIAS; the blue
component 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 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 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 (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 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 (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 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 (2^n)-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, -inf/inf)
GL_INDEX_OFFSET (integer, 0, -inf/inf)
GL_RED_SCALE (float, 1, -inf/inf)
GL_GREEN_SCALE (float, 1, -inf/inf)
GL_BLUE_SCALE (float, 1, -inf/inf)
GL_ALPHA_SCALE (float, 1, -inf/inf)
GL_DEPTH_SCALE (float, 1, -inf/inf)
GL_RED_BIAS (float, 0, -inf/inf)
GL_GREEN_BIAS (float, 0, -inf/inf)
GL_BLUE_BIAS (float, 0, -inf/inf)
GL_ALPHA_BIAS (float, 0, -inf/inf)
GL_DEPTH_BIAS (float, 0, -inf/inf)
GL_POST_COLOR_MATRIX_RED_SCALE (float, 1, -inf/inf)
GL_POST_COLOR_MATRIX_GREEN_SCALE (float, 1, -inf/inf)
GL_POST_COLOR_MATRIX_BLUE_SCALE (float, 1, -inf/inf)
GL_POST_COLOR_MATRIX_ALPHA_SCALE (float, 1, -inf/inf)
GL_POST_COLOR_MATRIX_RED_BIAS (float, 0, -inf/inf)
GL_POST_COLOR_MATRIX_GREEN_BIAS (float, 0, -inf/inf)
GL_POST_COLOR_MATRIX_BLUE_BIAS (float, 0, -inf/inf)
GL_POST_COLOR_MATRIX_ALPHA_BIAS (float, 0, -inf/inf)
GL_POST_CONVOLUTION_RED_SCALE (float, 1, -inf/inf)
GL_POST_CONVOLUTION_GREEN_SCALE (float, 1, -inf/inf)
GL_POST_CONVOLUTION_BLUE_SCALE (float, 1, -inf/inf)
GL_POST_CONVOLUTION_ALPHA_SCALE (float, 1, -inf/inf)
GL_POST_CONVOLUTION_RED_BIAS (float, 0, -inf/inf)
GL_POST_CONVOLUTION_GREEN_BIAS (float, 0, -inf/inf)
GL_POST_CONVOLUTION_BLUE_BIAS (float, 0, -inf/inf)
GL_POST_CONVOLUTION_ALPHA_BIAS (float, 0, -inf/inf)
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 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 parame-ters parameters
ters are set to false if param is 0 and to true otherwise. param is converted to floating point
before being assigned 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 exe-cuted executed
cuted are the ones that are used. They may be different from the settings when the command was com-piled compiled
piled 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
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(3G), glColorTable(3G), glColorSubTable(3G), glConvolutionFilter1D(3G), glConvolutionFilter2D(3G),
glCopyPixels(3G), glCopyTexImage1D(3G), glCopyTexImage2D(3G), glCopyTexSubImage1D(3G), glCopyTexSubImage2D(3G),
glCopyTexSubImage3D(3G), glDrawPixels(3G), glNewList(3G), glPixelMap(3G), glPixelStore(3G), glPixelZoom(3G), glReadPixels(3G),
glTexImage1D(3G), glTexImage2D(3G), glTexImage3D(3G), glTexSubImage1D(3G), glTexSubImage2D(3G), glTexSubImage3D(3G)
GLPIXELTRANSFER(3G)
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