void glPixelTransferf(GLenum pname,
GLfloat param)
void glPixelTransferi(GLenum pname,
GLint param)
Pixel transfer operations handle four fundamental pixel types: color, color index, depth, and stencil. Color pixels are made up of four floating-point values with unspecified mantissa and exponent sizes, scaled such that 0.0 represents zero intensity and 1.0 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:
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.
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 are specified with glPixelMap.
If the resulting pixels are to be written to an RGBA color buffer, or if they are being 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 are specified with glPixelMap.
glPixelTransferf can be used to set any pixel transfer parameter. If the parameter type is Boolean, 0.0 implies false and any other value implies true. If pname is an integer parameter, param is rounded to the nearest integer.
Likewise, glPixelTransferi can also be used to set any of the pixel transfer parameters. Boolean parameters are set to false if param is 0 and true otherwise. param is converted to floating point before being assigned to real-valued parameters.
GL_INVALID_OPERATION is generated if glPixelTransfer is called between a call to glBegin and the corresponding call to glEnd.
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© 1995 Uwe Behrens. All rights reserved.