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glHistogram - define histogram table
GLboolean sink )
eqn not supported
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
table entry to be incremented.) If a histogram table entry is incremented
beyond its maximum value, then its value becomes undefined. (This is not
- The histogram whose parameters are to
be set. Must be one of GL_HISTOGRAM or GL_PROXY_HISTOGRAM.
- The number
of entries in the histogram table. Must be a power of 2.
- 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.
- 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.
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
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 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.
glHistogram is present only if GL_ARB_imaging
is returned when glGetString is called with an argument of GL_EXTENSIONS.
GL_INVALID_ENUM is generated if target is not one of the allowable
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.
is generated if glHistogram is executed between the execution of glBegin
and the corresponding execution of glEnd.
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