1GLHISTOGRAM(3G) OpenGL Manual GLHISTOGRAM(3G)
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6 glHistogram - define histogram table
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9 void glHistogram(GLenum target, GLsizei width, GLenum internalformat,
10 GLboolean sink);
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13 target
14 The histogram whose parameters are to be set. Must be one of
15 GL_HISTOGRAM or GL_PROXY_HISTOGRAM.
16 width
18 The number of entries in the histogram table. Must be a power of 2.
19 internalformat
21 The format of entries in the histogram table. Must be one of
22 GL_ALPHA, GL_ALPHA4, GL_ALPHA8, GL_ALPHA12, GL_ALPHA16,
23 GL_LUMINANCE, GL_LUMINANCE4, GL_LUMINANCE8, GL_LUMINANCE12,
24 GL_LUMINANCE16, GL_LUMINANCE_ALPHA, GL_LUMINANCE4_ALPHA4,
25 GL_LUMINANCE6_ALPHA2, GL_LUMINANCE8_ALPHA8, GL_LUMINANCE12_ALPHA4,
26 GL_LUMINANCE12_ALPHA12, GL_LUMINANCE16_ALPHA16, GL_R3_G3_B2,
27 GL_RGB, GL_RGB4, GL_RGB5, GL_RGB8, GL_RGB10, GL_RGB12, GL_RGB16,
28 GL_RGBA, GL_RGBA2, GL_RGBA4, GL_RGB5_A1, GL_RGBA8, GL_RGB10_A2,
29 GL_RGBA12, or GL_RGBA16.
30 sink
32 If GL_TRUE, pixels will be consumed by the histogramming process
33 and no drawing or texture loading will take place. If GL_FALSE,
34 pixels will proceed to the minmax process after histogramming.
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37 When GL_HISTOGRAM is enabled, RGBA color components are converted to
38 histogram table indices by clamping to the range [0,1], multiplying by
39 the width of the histogram table, and rounding to the nearest integer.
40 The table entries selected by the RGBA indices are then incremented.
41 (If the internal format of the histogram table includes luminance, then
42 the index derived from the R color component determines the luminance
43 table entry to be incremented.) If a histogram table entry is
44 incremented beyond its maximum value, then its value becomes undefined.
45 (This is not an error.)
46 Histogramming is performed only for RGBA pixels (though these may be
48 specified originally as color indices and converted to RGBA by index
49 table lookup). Histogramming is enabled with glEnable() and disabled
50 with glDisable().
51 When target is GL_HISTOGRAM, glHistogram redefines the current
53 histogram table to have width entries of the format specified by
54 internalformat. The entries are indexed 0 through width - 1, and all
55 entries are initialized to zero. The values in the previous histogram
56 table, if any, are lost. If sink is GL_TRUE, then pixels are discarded
57 after histogramming; no further processing of the pixels takes place,
58 and no drawing, texture loading, or pixel readback will result.
59 When target is GL_PROXY_HISTOGRAM, glHistogram computes all state
61 information as if the histogram table were to be redefined, but does
62 not actually define the new table. If the requested histogram table is
63 too large to be supported, then the state information will be set to
64 zero. This provides a way to determine if a histogram table with the
65 given parameters can be supported.
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68 glHistogram is present only if ARB_imaging is returned when
69 glGetString() is called with an argument of GL_EXTENSIONS.
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72 GL_INVALID_ENUM is generated if target is not one of the allowable
73 values.
74 GL_INVALID_VALUE is generated if width is less than zero or is not a
76 power of 2.
77 GL_INVALID_ENUM is generated if internalformat is not one of the
79 allowable values.
80 GL_TABLE_TOO_LARGE is generated if target is GL_HISTOGRAM and the
82 histogram table specified is too large for the implementation.
83 GL_INVALID_OPERATION is generated if glHistogram is executed between
85 the execution of glBegin() and the corresponding execution of glEnd().
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88 glGetHistogramParameter()
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91 glGetHistogram(), glResetHistogram()
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94 Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
95 under the SGI Free Software B License. For details, see
96 http://oss.sgi.com/projects/FreeB/.
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