glPixelTransferi
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 )
delim $$
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 trans-
fer 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 opera-
tion. 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 float-
ing-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:
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 com-
ponent 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 compo-
nent 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 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
transformation by the color matrix. That is, the red com-
ponent 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 mul-
tiplied by GL_POST_CONVOLUTION_GREEN_SCALE, then added to
GL_POST_CONVOLUTION_GREEN_BIAS; the blue component is mul-
tiplied 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 pix-
els 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 speci-
fied 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 compo-
nents 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 $2 sup n
~-~ 1$, 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 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_COLOR_MATRIX_BLUE_SCALE float 1 (-∞,∞)
GL_POST_COLOR_MATRIX_ALPHA_SCALE float 1 (-∞,∞)
GL_POST_COLOR_MATRIX_RED_BIAS float 0 (-∞,∞)
GL_POST_COLOR_MATRIX_GREEN_BIAS float 0 (-∞,∞)
GL_POST_COLOR_MATRIX_BLUE_BIAS float 0 (-∞,∞)
GL_POST_COLOR_MATRIX_ALPHA_BIAS float 0 (-∞,∞)
GL_POST_CONVOLUTION_RED_SCALE float 1 (-∞,∞)
GL_POST_CONVOLUTION_GREEN_SCALE float 1 (-∞,∞)
GL_POST_CONVOLUTION_BLUE_SCALE float 1 (-∞,∞)
GL_POST_CONVOLUTION_ALPHA_SCALE float 1 (-∞,∞)
GL_POST_CONVOLUTION_RED_BIAS float 0 (-∞,∞)
GL_POST_CONVOLUTION_GREEN_BIAS float 0 (-∞,∞)
GL_POST_CONVOLUTION_BLUE_BIAS float 0 (-∞,∞)
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
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 trans-
fer 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 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
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)
