GLHISTOGRAM(3G)GLHISTOGRAM(3G)NAMEglHistogram - define histogram table
C SPECIFICATION
void glHistogram( GLenum target,
GLsizei width,
GLenum internalformat,
GLboolean sink )
delim $$
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 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 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.
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.
NOTESglHistogram 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 execution of glEnd.
ASSOCIATED GETS
glGetHistogramParameter
SEE ALSOglGetHistogram(3G), glResetHistogram(3G)
March 1, 2011
