define histogram table
glHistogram( GLenum ( target ) , GLsizei ( width ) , GLenum ( internalformat ) , GLboolean ( sink ) )-> void
When GL_HISTOGRAM is enabled, RGBA color components are converted to histogram table indices by clamping to the range [0,1], multiplying by the width of the histogram table, and rounding to the nearest integer. The table entries selected by the RGBA indices are then incremented. (If the internal format of the histogram table includes luminance, then the index derived from the R color component determines the luminance table entry to be incremented.) If a histogram table entry is incremented beyond its maximum value, then its value becomes undefined. (This is not an error.)
Histogramming is performed only for RGBA pixels (though these may be specified originally as color indices and converted to RGBA by index table lookup). Histogramming is enabled with glEnable and disabled with glDisable .
When target is GL_HISTOGRAM , glHistogram redefines the current histogram table to have width entries of the format specified by internalformat . The entries are indexed 0 through , and all entries are initialized to zero. The values in the previous histogram table, if any, are lost. If sink is GL_TRUE , then pixels are discarded after histogramming; no further processing of the pixels takes place, and no drawing, texture loading, or pixel readback will result.
When target is GL_PROXY_HISTOGRAM , glHistogram computes all state information as if the histogram table were to be redefined, but does not actually define the new table. If the requested histogram table is too large to be supported, then the state information will be set to zero. This provides a way to determine if a histogram table with the given parameters can be supported.
GL_INVALID_ENUM is generated if target is not one of the allowable values.
GL_INVALID_VALUE is generated if width is less than zero or is not a power of 2.
GL_INVALID_ENUM is generated if internalformat is not one of the allowable values.
GL_TABLE_TOO_LARGE is generated if target is GL_HISTOGRAM and the histogram table specified is too large for the implementation.
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/ .
Sample Code References
The following code samples have been found which appear to reference the functions described here. Take care that the code may be old, broken or not even use PyOpenGL.
OpenGLContext tests/glhistogram.py Lines: 42