glGetHistogramEXT(3G)	       OpenGL Reference		 glGetHistogramEXT(3G)



NAME
     glGetHistogramEXT - get histogram table


C SPECIFICATION
     void glGetHistogramEXT( GLenum target,
			     GLboolean reset,
			     GLenum format,
			     GLenum type,
			     GLvoid *values )


PARAMETERS
     target  Must be GL_HISTOGRAM_EXT.

     reset   If	GL_TRUE, each component	counter	that is	actually returned is
	     reset to zero.  (Other counters are unaffected.)  If GL_FALSE,
	     none of the counters in the histogram table is modified.

     format  The format	of values to be	returned in values.  Must be one of
	     GL_RED, GL_GREEN, GL_BLUE,	GL_ALPHA, GL_RGB, GL_RGBA,
	     GL_ABGR_EXT, GL_LUMINANCE,	or GL_LUMINANCE_ALPHA.

     type    The type of values	to be returned in values.  Must	be one of
	     GL_UNSIGNED_BYTE, GL_BYTE,	GL_UNSIGNED_SHORT, GL_SHORT,
	     GL_UNSIGNED_INT, GL_INT, GL_FLOAT,	GL_UNSIGNED_BYTE_3_3_2_EXT,
	     GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT,
	     GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT.

     values  A pointer to storage for the returned histogram table.

DESCRIPTION
     glGetHistogramEXT returns the current histogram table as a	one-
     dimensional image with the	same width as the histogram.  No pixel
     transfer operations are performed on this image, but pixel	storage	modes
     that are applicable to 1D images are honored.

     Color components that are requested in the	specified format, but which
     are not included in the internal format of	the histogram, are returned as
     zero.  The	assignments of internal	color components to the	components
     requested by format are:

		       Internal	Component   Result Component
		       _____________________________________
		       red		    red
		       green		    green
		       blue		    blue
		       alpha		    alpha
		       luminance	    red






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glGetHistogramEXT(3G)	       OpenGL Reference		 glGetHistogramEXT(3G)



ERRORS
     GL_INVALID_ENUM is	generated if target is not GL_HISTOGRAM_EXT.

     GL_INVALID_ENUM is	generated if format is not one of the allowable
     values.

     GL_INVALID_ENUM is	generated if type is not one of	the allowable values.

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

     If	type is	set to GL_UNSIGNED_BYTE_3_3_2_EXT,
     GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT,
     GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT and	the
     EXT_packed_pixels extension is not	supported then a GL_INVALID_ENUM error
     is	generated.


MACHINE	DEPENDENCIES
     On	RealityEngine, RealityEngine2, and VTX systems,	histogram and minmax
     may not be	used when rendering to pixmaps.

     On	InfiniteReality	systems	selection and histogramming are	unreliable if
     interrupted by a graphics context switch.	This will be fixed in the next
     software release.


SEE ALSO
     glHistogramEXT, glResetHistogramEXT, glGetHistogramParameterEXT.

























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