<div class="refentry" title="glLogicOp"><a id="glLogicOp"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glLogicOp — specify a logical pixel operation</p></div><div class="refsynopsisdiv" title="C Specification"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glLogicOp</b>(</code></td><td>GLenum <var class="pdparam">opcode</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Parameters"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term">

<em class="parameter"><code>opcode</code></em>

</span></dt><dd><p>Specifies a symbolic constant that selects a

logical operation. The following symbols are accepted:

<code class="constant">GL_CLEAR</code>,

<code class="constant">GL_SET</code>,

<code class="constant">GL_COPY</code>,

<code class="constant">GL_COPY_INVERTED</code>,

<code class="constant">GL_NOOP</code>,

<code class="constant">GL_INVERT</code>,

<code class="constant">GL_AND</code>,

<code class="constant">GL_NAND</code>,

<code class="constant">GL_OR</code>,

<code class="constant">GL_NOR</code>,

<code class="constant">GL_XOR</code>,

<code class="constant">GL_EQUIV</code>,

<code class="constant">GL_AND_REVERSE</code>,

<code class="constant">GL_AND_INVERTED</code>,

<code class="constant">GL_OR_REVERSE</code>, and

<code class="constant">GL_OR_INVERTED</code>. The initial value is

<code class="constant">GL_COPY</code>.</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="description"></a><h2>Description</h2><p><code class="function">glLogicOp</code>

specifies a logical operation that, when enabled, is applied

between the incoming color and the color at the corresponding

location in the frame buffer.

To enable or disable the logical operation, call

<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and

<a class="citerefentry" href="glDisable"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a>

with argument <code class="constant">GL_COLOR_LOGIC_OP</code>.

Logical operation is initially disabled.

</p><div class="informaltable"><table><colgroup><col /><col /></colgroup><thead><tr><th>Opcode</th><th class="center">Resulting Operation</th></tr></thead><tbody><tr><td><code class="constant">GL_CLEAR</code></td><td class="center">0</td></tr><tr><td><code class="constant">GL_SET</code></td><td class="center">1</td></tr><tr><td><code class="constant">GL_COPY</code></td><td class="center"><em class="replaceable"><code>s</code></em></td></tr><tr><td><code class="constant">GL_COPY_INVERTED</code></td><td class="center">

<math overflow="scroll">

<mo>~</mo><mi>s</mi>

</math>

</td></tr><tr><td><code class="constant">GL_NOOP</code></td><td class="center"><em class="replaceable"><code>d</code></em></td></tr><tr><td><code class="constant">GL_INVERT</code></td><td class="center">

<math overflow="scroll">

<mo>~</mo><mi>d</mi>

</math>

</td></tr><tr><td><code class="constant">GL_AND</code></td><td class="center">

<math overflow="scroll">

<mi>s</mi><mo>&amp;</mo><mi>d</mi>

</math>

</td></tr><tr><td><code class="constant">GL_NAND</code></td><td class="center">

<math overflow="scroll">

<mo>~</mo><mfenced><mrow><mi>s</mi><mo>&amp;</mo><mi>d</mi></mrow></mfenced>

</math>

</td></tr><tr><td><code class="constant">GL_OR</code></td><td class="center">

<math overflow="scroll">

<mi>s</mi><mo>|</mo><mi>d</mi>

</math>

</td></tr><tr><td><code class="constant">GL_NOR</code></td><td class="center">

<math overflow="scroll">

<mo>~</mo><mfenced><mrow><mi>s</mi><mo>|</mo><mi>d</mi></mrow></mfenced>

</math>

</td></tr><tr><td><code class="constant">GL_XOR</code></td><td class="center">

<math overflow="scroll">

<mi>s</mi><mo>^</mo><mi>d</mi>

</math>

</td></tr><tr><td><code class="constant">GL_EQUIV</code></td><td class="center">

<math overflow="scroll">

<mo>~</mo><mfenced><mrow><mi>s</mi><mo>^</mo><mi>d</mi></mrow></mfenced>

</math>

</td></tr><tr><td><code class="constant">GL_AND_REVERSE</code></td><td class="center">

<math overflow="scroll">

<mi>s</mi><mo>&amp;</mo><mo>~</mo><mi>d</mi>

</math>

</td></tr><tr><td><code class="constant">GL_AND_INVERTED</code></td><td class="center">

<math overflow="scroll">

<mo>~</mo><mi>s</mi><mo>&amp;</mo><mi>d</mi>

</math>

</td></tr><tr><td><code class="constant">GL_OR_REVERSE</code></td><td class="center">

<math overflow="scroll">

<mi>s</mi><mo>|</mo><mo>~</mo><mi>d</mi>

</math>

</td></tr><tr><td><code class="constant">GL_OR_INVERTED</code></td><td class="center">

<math overflow="scroll">

<mo>~</mo><mi>s</mi><mo>|</mo><mi>d</mi>

</math>

</td></tr></tbody></table></div><p>

<em class="parameter"><code>opcode</code></em>

is a symbolic constant chosen from the list above. In the

explanation of the logical operations, <em class="parameter"><code>s</code></em>

represents the incoming color and <em class="parameter"><code>d</code></em>

represents the color in the frame buffer. Standard C-language

operators are used. As these bitwise operators suggest, the

logical operation is applied independently to each bit pair of

the source and destination indices or colors.</p></div><div class="refsect1" title="Errors"><a id="errors"></a><h2>Errors</h2><p><code class="constant">GL_INVALID_ENUM</code> is generated if

<em class="parameter"><code>opcode</code></em> is not an accepted value.</p></div><div class="refsect1" title="See Also"><a id="seealso"></a><h2>See Also</h2><p>

<a class="citerefentry" href="glAlphaFunc"><span class="citerefentry"><span class="refentrytitle">glAlphaFunc</span></span></a>,

<a class="citerefentry" href="glBlendFunc"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a>,

<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,

<a class="citerefentry" href="glStencilOp"><span class="citerefentry"><span class="refentrytitle">glStencilOp</span></span></a>

</p></div><div class="refsect1" title="Copyright"><a id="copyright"></a><h2>Copyright</h2><p>

Copyright © 2003-2004

Silicon Graphics, Inc. This document is licensed under the SGI

Free Software B License. For details, see

<a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.

</p></div></div>