GLHISTOGRAM(3G) 														   GLHISTOGRAM(3G)

NAME

       glHistogram - define histogram table

C SPECIFICATION

       void glHistogram( GLenum target,
			 GLsizei width,
			 GLenum internalformat,
			 GLboolean sink )

PARAMETERS

       target	       The histogram whose parameters are to be set.  Must be one of GL_HISTOGRAM or GL_PROXY_HISTOGRAM.

       width	       The number of entries in the histogram table.  Must be a power of 2.

       internalformat  The   of  entries  in  the  histogram  table.   Must  be  one  of  GL_ALPHA,  GL_ALPHA4, GL_ALPHA8, GL_ALPHA12, GL_ALPHA16,
		       GL_LUMINANCE,  GL_LUMINANCE4,  GL_LUMINANCE8,  GL_LUMINANCE12,  GL_LUMINANCE16,	GL_LUMINANCE_ALPHA,  GL_LUMINANCE4_ALPHA4,
		       GL_LUMINANCE6_ALPHA2,	GL_LUMINANCE8_ALPHA8,	GL_LUMINANCE12_ALPHA4,	 GL_LUMINANCE12_ALPHA12,   GL_LUMINANCE16_ALPHA16,
		       GL_R3_G3_B2, GL_RGB, GL_RGB4, GL_RGB5, GL_RGB8, GL_RGB10, GL_RGB12,  GL_RGB16,  GL_RGBA,  GL_RGBA2,  GL_RGBA4,  GL_RGB5_A1,
		       GL_RGBA8, GL_RGB10_A2, GL_RGBA12, or GL_RGBA16.

       sink	       If  GL_TRUE,  pixels  will  be consumed by the histogramming process and no drawing or texture loading will take place.	If
		       GL_FALSE, pixels will proceed to the minmax process after histogramming.

DESCRIPTION

       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 incre-
       mented.	(If the internal  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 unde-
       fined.  (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  specified by internalformat.
       The entries are indexed 0 through width - 1, 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 draw-
       ing, 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.

NOTES

       glHistogram is present only if GL_ARB_imaging is returned when glGetString is called with an argument of GL_EXTENSIONS.

ERRORS

       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.

       GL_INVALID_OPERATION is generated if glHistogram is executed between the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

       glGetHistogramParameter

SEE ALSO

       glGetHistogram, glResetHistogram

																   GLHISTOGRAM(3G)