fglHistogramEXT(3G) OpenGL Reference fglHistogramEXT(3G)NAME
fglHistogramEXT - define histogram table
FORTRAN SPECIFICATION
SUBROUTINE fglHistogramEXT( INTEGER*4 target,
INTEGER*4 width,
INTEGER*4 internalformat,
LOGICAL*1 sink )
PARAMETERS
target The histogram whose parameters are to be set. Must be
one of GL_HISTOGRAM_EXT or GL_PROXY_HISTOGRAM_EXT.
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_EXT, GL_ALPHA8_EXT,
GL_ALPHA12_EXT, GL_ALPHA16_EXT, GL_LUMINANCE,
GL_LUMINANCE4_EXT, GL_LUMINANCE8_EXT, GL_LUMINANCE12_EXT,
GL_LUMINANCE16_EXT, GL_LUMINANCE_ALPHA,
GL_LUMINANCE4_ALPHA4_EXT, GL_LUMINANCE6_ALPHA2_EXT,
GL_LUMINANCE8_ALPHA8_EXT, GL_LUMINANCE12_ALPHA4_EXT,
GL_LUMINANCE12_ALPHA12_EXT, GL_LUMINANCE16_ALPHA16_EXT,
GL_RGB, GL_RGB2_EXT, GL_RGB4_EXT, GL_RGB5_EXT,
GL_RGB8_EXT, GL_RGB10_EXT, GL_RGB12_EXT, GL_RGB16_EXT,
GL_RGBA, GL_RGBA2_EXT, GL_RGBA4_EXT, GL_RGB5_A1_EXT,
GL_RGBA8_EXT, GL_RGB10_A2_EXT, GL_RGBA12_EXT, or
GL_RGBA16_EXT.
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.
DESCRIPTION
Histogramming is part of the OpenGL pixel transfer process. It takes
place immediately after index lookup. 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 fglEnable and disabled with fglDisable.
When GL_HISTOGRAM_EXT 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
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fglHistogramEXT(3G) OpenGL Reference fglHistogramEXT(3G)
an error.)
When target is GL_HISTOGRAM_EXT, fglHistogramEXT 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_EXT, fglHistogramEXT computes all state
information as if the histogram table was 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.
The histogram state information may be queried by calling
fglGetHistogramParameterEXT with a target of GL_HISTOGRAM_EXT (to obtain
information for the current histogram table) or GL_PROXY_HISTOGRAM_EXT
(to obtain information from the most recent proxy request) and one of the
following values for the pname argument:
Parameter Description
___________________________________________________________________________
GL_HISTOGRAM_WIDTH_EXT Histogram table width
GL_HISTOGRAM_FORMAT_EXT Internal format
GL_HISTOGRAM_RED_SIZE_EXT Red component counter size, in bits
GL_HISTOGRAM_GREEN_SIZE_EXT Green component counter size, in bits
GL_HISTOGRAM_BLUE_SIZE_EXT Blue component counter size, in bits
GL_HISTOGRAM_ALPHA_SIZE_EXT Alpha component counter size, in bits
GL_HISTOGRAM_LUMINANCE_SIZE_EXT Luminance component counter size, in bits
GL_HISTOGRAM_SINK_EXT Value of the sink parameter
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_EXT is generated if target is GL_HISTOGRAM_EXT and the
histogram table specified is too large for the implementation.
GL_INVALID_OPERATION is generated if fglHistogramEXT is executed between
the execution of fglBegin and the corresponding execution of fglEnd.
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fglHistogramEXT(3G) OpenGL Reference fglHistogramEXT(3G)ASSOCIATED GETS
fglGetHistogramParameterEXT.
MACHINE DEPENDENCIES
On RealityEngine, RealityEngine2, and VTX systems, histogram and minmax
may not be used when rendering to pixmaps.
SEE ALSO
fglGetHistogramEXT, fglResetHistogramEXT.
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