NAME
fglPixelTransferf, fglPixelTransferi - set pixel transfer
modes
FORTRAN SPECIFICATION
SUBROUTINE fglPixelTransferf( INTEGER*4 pname,
REAL*4 param )
SUBROUTINE fglPixelTransferi( INTEGER*4 pname,
INTEGER*4 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.
param Specifies the value that pname is set to.
DESCRIPTION
fglPixelTransfer sets pixel transfer modes that affect the
operation of subsequent fglCopyPixels, fglCopyTexImage1D,
fglCopyTexImage2D, fglCopyTexSubImage1D,
fglCopyTexSubImage2D, fglDrawPixels, fglReadPixels,
fglTexImage1D, fglTexImage2D, fglTexSubImage1D, and
fglTexSubImage2D commands. The algorithms that are
specified by pixel transfer modes operate on pixels after
they are read from the frame buffer (fglCopyPixels
fglCopyTexImage1D, fglCopyTexImage2D, fglCopyTexSubImage1D,
fglCopyTexSubImage2D, and fglReadPixels), or unpacked from
client memory (fglDrawPixels, fglTexImage1D, fglTexImage2D,
fglTexSubImage1D, and fglTexSubImage2D). 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 fglPixelStore) 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:
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 fglPixelTransfer.
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 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 fglPixelTransfer. The
contents of the various maps are specified with
fglPixelMap.
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
fglPixelTransfer.
From this point, operation diverges depending on
the required format 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 format,
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 fglPixelTransfer.
The contents of the index map is specified with
fglPixelMap.
If the resulting pixels are to be written to an
RGBA color buffer, or if they are read back to
client memory in a format 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
fglPixelMap.
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 fglPixelTransfer.
_________________________________________________________
| 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 | (-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) |
|________________|_________|_______________|_____________|
fglPixelTransferf 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, fglPixelTransferi 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 real-
valued parameters.
NOTES
If a fglCopyPixels, fglCopyTexImage1D, fglCopyTexImage2D,
fglCopyTexSubImage1D, fglCopyTexSubImage2D, fglDrawPixels,
fglReadPixels, fglTexImage1D, fglTexImage2D,
fglTexSubImage1D, or fglTexSubImage2D command is placed in a
display list (see fglNewList and fglCallList), 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 fglPixelTransfer is
executed between the execution of fglBegin and the
corresponding execution of fglEnd.
ASSOCIATED GETS
fglGet with argument GL_MAP_COLOR
fglGet with argument GL_MAP_STENCIL
fglGet with argument GL_INDEX_SHIFT
fglGet with argument GL_INDEX_OFFSET
fglGet with argument GL_RED_SCALE
fglGet with argument GL_RED_BIAS
fglGet with argument GL_GREEN_SCALE
fglGet with argument GL_GREEN_BIAS
fglGet with argument GL_BLUE_SCALE
fglGet with argument GL_BLUE_BIAS
fglGet with argument GL_ALPHA_SCALE
fglGet with argument GL_ALPHA_BIAS
fglGet with argument GL_DEPTH_SCALE
fglGet with argument GL_DEPTH_BIAS
SEE ALSO
fglCallList, fglCopyPixels, fglCopyTexImage1D,
fglCopyTexImage2D, fglCopyTexSubImage1D,
fglCopyTexSubImage2D, fglDrawPixels, fglNewList,
fglPixelMap, fglPixelStore, fglPixelZoom, fglReadPixels,
fglTexImage1D, fglTexImage2D, fglTexSubImage1D,
fglTexSubImage2D