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glPixelTransfer(3G)
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glPixelTransfer, glPixelTransferf, glPixelTransferi - set
pixel transfer modes
void glPixelTransferf(
GLenum pname,
GLfloat param ); void glPixelTransferi(
GLenum pname,
GLint param );
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.
Specifies the value that pname is set to.
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 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 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 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 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 precision to the right of the binary point.
The pixel transfer operations performed on the four basic
pixel types are as follows: 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-tocolor
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().
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 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 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]. 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 sup 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 sup 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(). Each depth value is
multiplied by GL_DEPTH_SCALE, added to
GL_DEPTH_BIAS, then clamped to the range [0,1].
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
sup 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 Valid Range
Value
---------------------------------------------------------------------
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 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 assigned to realvalued
parameters.
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.
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().
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
glCallList(3), glColorTable(3), glColorSubTable(3), glConvolutionFilter1D(3), glConvolutionFilter2D(3), glCopyPixels(3), glCopyTexImage1D(3), glCopyTexImage2D(3), glCopyTexSubImage1D(3), glCopyTexSubImage2D(3), glCopyTexSubImage3D(3), glDrawPixels(3), glNewList(3), glPixelMap(3),
glPixelStore(3), glPixelZoom(3), glReadPixels(3), glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), glTexSubImage1D(3), glTexSubImage2D(3), glTexSubImage3D(3)
glPixelTransfer(3G)
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