glHistogram(3G) OpenGL Reference glHistogram(3G)
glHistogram - define histogram table
void glHistogram( GLenum target,
GLsizei width,
GLenum internalformat,
GLboolean sink )
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 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.
sink 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.
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 incremented
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.
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glHistogram(3G) OpenGL Reference glHistogram(3G)
When target is GL_HISTOGRAM, glHistogram redefines the current histogram
table to have width entries of the format 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
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
histogram 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.
glGetHistogramParameter
glGetHistogram, glResetHistogram
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