GLPIXELTRANSFER(3G)

NAME
glPixelTransfer - set pixel transfer modes

C SPECIFICATION

void glPixelTransferf(GLenum pname, GLfloat param);

void glPixelTransferi(GLenum pname, GLint 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.

    Additionally, if the 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. Additionally, if the 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:

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 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 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.

    Similarly, if the 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.

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 true, each index is masked by 2 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 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 2 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().

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 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 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 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(), glColorTable(), glColorSubTable(), glConvolutionFilter1D(), glConvolutionFilter2D(), glCopyPixels(), glCopyTexImage1D(), glCopyTexImage2D(), glCopyTexSubImage1D(), glCopyTexSubImage2D(), glCopyTexSubImage3D(), glDrawPixels(), glNewList(), glPixelMap(), glPixelStore(), glPixelZoom(), glReadPixels(), glTexImage1D(), glTexImage2D(), glTexImage3D(), glTexSubImage1D(), glTexSubImage2D(), glTexSubImage3D()

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.