C SPECIFICATION

       void GLAPIENTRY glHistogram( GLenum target,
                                    GLsizei widt )

PARAMETERS

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

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

       _param3 The  format  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.

       _param4 If GL_TRUE, pixels will be consumed by the  histogramming  pro-
               cess  and  no  drawing  or texture loading will take place.  If
               GL_FALSE, pixels will proceed to the minmax process after  his-
               togramming.

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 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 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 widt entries of the format specified by _param3.
       The entries are indexed 0 through widt-1, and all entries are  initial-
       ized  to zero.  The values in the previous histogram table, if any, are
       lost.  If _param4 is GL_TRUE, then  pixels  are  discarded  after  his-
       togramming;  no  further  processing  of the pixels takes place, and no
       drawing, texture loading, or pixel readback will result.
       GL_INVALID_ENUM is generated if target is not one of the allowable val-
       ues.

       GL_INVALID_VALUE  is  generated  if  widt is less than zero or is not a
       power of 2.

       GL_INVALID_ENUM is generated if _param3 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, glResetHistogram



                                                               GLHISTOGRAM(3G)