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1 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> |
2 | <!-- saved from url=(0013)about:internet --> | |
3 | <?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>glHistogram</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glHistogram"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glHistogram — define histogram table</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glHistogram</b>(</code></td><td>GLenum </td><td><var class="pdparam">target</var>, </td></tr><tr><td> </td><td>GLsizei </td><td><var class="pdparam">width</var>, </td></tr><tr><td> </td><td>GLenum </td><td><var class="pdparam">internalformat</var>, </td></tr><tr><td> </td><td>GLboolean </td><td><var class="pdparam">sink</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>target</code></em></span></dt><dd><p> | |
4 | The histogram whose parameters are to be set. | |
5 | Must be one of | |
6 | <code class="constant">GL_HISTOGRAM</code> or | |
7 | <code class="constant">GL_PROXY_HISTOGRAM</code>. | |
8 | </p></dd><dt><span class="term"><em class="parameter"><code>width</code></em></span></dt><dd><p> | |
9 | The number of entries in the histogram table. Must be a power of 2. | |
10 | </p></dd><dt><span class="term"><em class="parameter"><code>internalformat</code></em></span></dt><dd><p> | |
11 | The format of entries in the histogram table. | |
12 | Must be one of | |
13 | <code class="constant">GL_ALPHA</code>, | |
14 | <code class="constant">GL_ALPHA4</code>, | |
15 | <code class="constant">GL_ALPHA8</code>, | |
16 | <code class="constant">GL_ALPHA12</code>, | |
17 | <code class="constant">GL_ALPHA16</code>, | |
18 | <code class="constant">GL_LUMINANCE</code>, | |
19 | <code class="constant">GL_LUMINANCE4</code>, | |
20 | <code class="constant">GL_LUMINANCE8</code>, | |
21 | <code class="constant">GL_LUMINANCE12</code>, | |
22 | <code class="constant">GL_LUMINANCE16</code>, | |
23 | <code class="constant">GL_LUMINANCE_ALPHA</code>, | |
24 | <code class="constant">GL_LUMINANCE4_ALPHA4</code>, | |
25 | <code class="constant">GL_LUMINANCE6_ALPHA2</code>, | |
26 | <code class="constant">GL_LUMINANCE8_ALPHA8</code>, | |
27 | <code class="constant">GL_LUMINANCE12_ALPHA4</code>, | |
28 | <code class="constant">GL_LUMINANCE12_ALPHA12</code>, | |
29 | <code class="constant">GL_LUMINANCE16_ALPHA16</code>, | |
30 | <code class="constant">GL_R3_G3_B2</code>, | |
31 | <code class="constant">GL_RGB</code>, | |
32 | <code class="constant">GL_RGB4</code>, | |
33 | <code class="constant">GL_RGB5</code>, | |
34 | <code class="constant">GL_RGB8</code>, | |
35 | <code class="constant">GL_RGB10</code>, | |
36 | <code class="constant">GL_RGB12</code>, | |
37 | <code class="constant">GL_RGB16</code>, | |
38 | <code class="constant">GL_RGBA</code>, | |
39 | <code class="constant">GL_RGBA2</code>, | |
40 | <code class="constant">GL_RGBA4</code>, | |
41 | <code class="constant">GL_RGB5_A1</code>, | |
42 | <code class="constant">GL_RGBA8</code>, | |
43 | <code class="constant">GL_RGB10_A2</code>, | |
44 | <code class="constant">GL_RGBA12</code>, or | |
45 | <code class="constant">GL_RGBA16</code>. | |
46 | </p></dd><dt><span class="term"><em class="parameter"><code>sink</code></em></span></dt><dd><p> | |
47 | If <code class="constant">GL_TRUE</code>, pixels will be consumed by the histogramming | |
48 | process and no drawing or texture loading will take place. | |
49 | If <code class="constant">GL_FALSE</code>, pixels will proceed to the minmax process after | |
50 | histogramming. | |
51 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p> | |
52 | When <code class="constant">GL_HISTOGRAM</code> is enabled, RGBA color components are converted to | |
53 | histogram table indices by clamping to the range [0,1], multiplying by | |
54 | the width of the histogram table, and rounding to the nearest integer. | |
55 | The table entries selected by the RGBA indices are then incremented. | |
56 | (If the internal format of the histogram table includes luminance, then | |
57 | the index derived from the R color component determines the luminance | |
58 | table entry to be incremented.) If a histogram table entry is incremented | |
59 | beyond its maximum value, then its value becomes undefined. (This is | |
60 | not an error.) | |
61 | </p><p> | |
62 | Histogramming is performed only for RGBA pixels (though these may | |
63 | be specified originally as color indices and converted to RGBA by | |
64 | index table lookup). | |
65 | Histogramming is enabled with <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and disabled with <a class="citerefentry" href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a>. | |
66 | </p><p> | |
67 | When <em class="parameter"><code>target</code></em> is <code class="constant">GL_HISTOGRAM</code>, <code class="function">glHistogram</code> redefines the current | |
68 | histogram table to have <em class="parameter"><code>width</code></em> entries of the format specified by | |
69 | <em class="parameter"><code>internalformat</code></em>. | |
70 | The entries are indexed 0 through | |
71 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
72 | ||
73 | <mml:mrow> | |
74 | <mml:mi mathvariant="italic">width</mml:mi> | |
75 | <mml:mo>-</mml:mo> | |
76 | <mml:mn>1</mml:mn> | |
77 | </mml:mrow> | |
78 | </mml:math>, | |
79 | and | |
80 | all entries are initialized to zero. | |
81 | The values in the previous histogram table, if any, are lost. | |
82 | If <em class="parameter"><code>sink</code></em> is <code class="constant">GL_TRUE</code>, then pixels are discarded after histogramming; | |
83 | no further processing of the pixels takes place, and no drawing, | |
84 | texture loading, or pixel readback will result. | |
85 | </p><p> | |
86 | When <em class="parameter"><code>target</code></em> is <code class="constant">GL_PROXY_HISTOGRAM</code>, <code class="function">glHistogram</code> computes all | |
87 | state information as if the histogram table were to be redefined, | |
88 | but does not actually define the new table. | |
89 | If the requested histogram table is too large to be supported, then the | |
90 | state information will be set to zero. | |
91 | This provides a way to determine if a histogram table with the given | |
92 | parameters can be supported. | |
93 | </p><p> | |
94 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p> | |
95 | <code class="function">glHistogram</code> is present only if <code class="code">ARB_imaging</code> is returned when <a class="citerefentry" href="glGetString.xml"><span class="citerefentry"><span class="refentrytitle">glGetString</span></span></a> | |
96 | is called with an argument of <code class="constant">GL_EXTENSIONS</code>. | |
97 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p> | |
98 | <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>target</code></em> is not one of the allowable | |
99 | values. | |
100 | </p><p> | |
101 | <code class="constant">GL_INVALID_VALUE</code> is generated if <em class="parameter"><code>width</code></em> is less than zero or is | |
102 | not a power of 2. | |
103 | </p><p> | |
104 | <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>internalformat</code></em> is not one of the | |
105 | allowable values. | |
106 | </p><p> | |
107 | <code class="constant">GL_TABLE_TOO_LARGE</code> is generated if <em class="parameter"><code>target</code></em> is <code class="constant">GL_HISTOGRAM</code> | |
108 | and the histogram table specified is too large for the implementation. | |
109 | </p><p> | |
110 | <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glHistogram</code> is executed | |
111 | between the execution of <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a> and the corresponding | |
112 | execution of <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>. | |
113 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p> | |
114 | <a class="citerefentry" href="glGetHistogramParameter.xml"><span class="citerefentry"><span class="refentrytitle">glGetHistogramParameter</span></span></a> | |
115 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p> | |
116 | <a class="citerefentry" href="glGetHistogram.xml"><span class="citerefentry"><span class="refentrytitle">glGetHistogram</span></span></a>, | |
117 | <a class="citerefentry" href="glResetHistogram.xml"><span class="citerefentry"><span class="refentrytitle">glResetHistogram</span></span></a> | |
118 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p> | |
119 | Copyright <span class="trademark"></span>© 1991-2006 | |
120 | Silicon Graphics, Inc. This document is licensed under the SGI | |
121 | Free Software B License. For details, see | |
122 | <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>. | |
123 | </p></div></div></body></html> |