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 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 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 ta‐
       ble lookup).  Histogramming is enabled with glEnable and  disabled  with
       glDisable.

       When target is GL_HISTOGRAM, glHistogram redefines the current histogram
       table to have widt entries of the format specified by _param3.  The  en‐
       tries  are  indexed 0 through widt−1, and all entries are initialized to
       zero.  The values in the previous histogram table, if any, are lost.  If
       _param4  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 infor‐
       mation as if the histogram table were to be redefined, but does not  ac‐
       tually  define  the  new table.  If the requested histogram table is too
       large to be supported, then the state information will be set  to  zero.
       GL_INVALID_ENUM is generated if _param3 is not one of the allowable val‐
       ues.

       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)