GLPIXELTRANSFER(3G) UNIX Programmer's Manual GLPIXELTRANSFER(3G)
glPixelTransferf, glPixelTransferi - set pixel transfer
modes
void glPixelTransferf( GLenum pname,
GLfloat param )
void glPixelTransferi( GLenum pname,
GLint param )
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 sup-
ported, 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.
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
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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 opera-
tions 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 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 unspeci-
fied precision to the right of the binary point. Depth pix-
els 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 max-
imum 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 component
is multiplied by GL_BLUE_SCALE, then added to
GL_BLUE_BIAS; and the alpha component is multi-
plied 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
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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 transformation 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 com-
ponent is multiplied by
GL_POST_COLOR_MATRIX_GREEN_SCALE, then added to
GL_POST_COLOR_MATRIX_GREEN_BIAS; the blue com-
ponent 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 com-
ponent 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
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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
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
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 con-
tents 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.
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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.
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 con-
verted to floating point before being assigned to real-
valued parameters.
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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 exe-
cuted 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
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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)
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