GLHISTOGRAM(3G) UNIX Programmer's Manual 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
histogramming process and no drawing or tex-
ture 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 con-
verted 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 an error.)
MirBSD #10-current Printed 2021-12-07 1
GLHISTOGRAM(3G) UNIX Programmer's Manual GLHISTOGRAM(3G)
Histogramming is performed only for RGBA pixels (though
these may be specified originally as color indices and con-
verted to RGBA by index table lookup). Histogramming is
enabled with glEnable and disabled with glDisable.
When target is GL_HISTOGRAM, glHistogram redefines the
current histogram table to have width entries of the speci-
fied 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 histogram-
ming; 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 rede-
fined, 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 parame-
ters 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 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 exe-
cution of glEnd.
ASSOCIATED GETS
glGetHistogramParameter
SEE ALSO
glGetHistogram(3G), glResetHistogram(3G)
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