glPixelTransfer(3G) OpenGL Reference 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 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.
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.
Page 1
glPixelTransfer(3G) OpenGL Reference glPixelTransfer(3G)
Pixel transfer operations handle four fundamental pixel types: color,
color index, depth, and stencil. Color pixels consist of four floatingpoint
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 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 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
Page 2
glPixelTransfer(3G) OpenGL Reference glPixelTransfer(3G)
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].
A color lookup is then performed if the SGI_color_table
extension is supported and
GL_POST_CONVOLUTION_COLOR_TABLE_SGI is enabled.
If the SGI_color_matrix extension is supported, then the
color components of each pixel are modified by multiplying
them with the matrix at the top of the color matrix stack,
scaling them by specified values, and then biasing
(offsetting) them by specified values. That is, if the
original color components are (R, G, B, A), and the matrix at
the top of the color matrix stack is represented by m1, m2,
..., m16, then the modified color components (R', G', B', A')
are given by:
R' = ((m1*R) + (m5*G) + (m9*B) + (m13*A))*Rscale + Rbias
G' = ((m2*R) + (m6*G) + (m10*B) + (m14*A))*Gscale + Gbias
B' = ((m3*R) + (m7*G) + (m11*B) + (m15*A))*Bscale + Bbias
A' = ((m4*R) + (m8*G) + (m12*B) + (m16*A))*Ascale + Abias
The color matrix is specified using any of the OpenGL matrix
commands when the matrix mode (see glMatrixMode) is GL_COLOR.
The scale and bias terms are specified by executing
glPixelTransfer with pname equal to
GL_POST_COLOR_MATRIX_RED_SCALE_SGI,
GL_POST_COLOR_MATRIX_GREEN_SCALE_SGI,
GL_POST_COLOR_MATRIX_BLUE_SCALE_SGI,
GL_POST_COLOR_MATRIX_ALPHA_SCALE_SGI,
GL_POST_COLOR_MATRIX_RED_BIAS_SGI,
GL_POST_COLOR_MATRIX_GREEN_BIAS_SGI,
GL_POST_COLOR_MATRIX_BLUE_BIAS_SGI, or
GL_POST_COLOR_MATRIX_ALPHA_BIAS_SGI and param equal to the
Page 3
glPixelTransfer(3G) OpenGL Reference glPixelTransfer(3G)
desired value.
A color lookup is also performed after the color matrix
operation if the SGI_color_matrix extension is supported, and
GL_PROXY_POST_COLOR_MATRIX_COLOR_TABLE_SGI is enabled.
If the EXT_histogram extension is supported, and
GL_HISTOGRAM_EXT is enabled, the pixels are histogrammed.
See glHistogramEXT for more information.
If the EXT_histogram extension is supported, and
GL_MINMAX_EXT is enabled, the minimum and maximum pixel
values are recorded. See glMinMaxEXT for more information.
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
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
n
true, each index is masked by 2 - 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 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
n
dereferenced, the index is masked by 2 - 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].
Page 4
glPixelTransfer(3G) OpenGL Reference glPixelTransfer(3G)
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
n
is true, each index is masked by 2 - 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 (-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.
Page 5
glPixelTransfer(3G) OpenGL Reference glPixelTransfer(3G)
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 real-valued 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
Page 6
glPixelTransfer(3G) OpenGL Reference glPixelTransfer(3G)
glGet with argument GL_POST_CONVOLUTION_ALPHA_BIAS
glCallList, glColorTable, glColorSubTable, glConvolutionFilter1D,
glConvolutionFilter2D, glCopyPixels, glCopyTexImage1D, glCopyTexImage2D,
glCopyTexSubImage1D, glCopyTexSubImage2D, glCopyTexSubImage3D,
glDrawPixels, glNewList, glPixelMap, glPixelStore, glPixelZoom,
glReadPixels, glTexImage1D, glTexImage2D, glTexImage3D, glTexSubImage1D,
glTexSubImage2D, glTexSubImage3D
PPPPaaaaggggeeee 7777 [ Back ]
|
