glHistogram

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 histogram-
		       ming 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 incremented.
       (If the internal	 of the histogram table includes luminance, then  the
       index  derived from the R color component determines the luminance ta-
       ble entry to be incremented.)  If a histogram table  entry  is  incre-
       mented  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 his-
       togram table to have width entries of the  specified  by	 internalfor-
       mat.   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
       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.


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 his-
       togram 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(3G), glResetHistogram(3G)



							      GLHISTOGRAM(3G)