<div class="refentry" lang="en" xml:lang="en"><a id="glBlendEquation"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glBlendEquation — specify the equation used for both the RGB blend equation and the Alpha blend equation</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glBlendEquation</b>(</code></td><td>GLenum  </td><td><var class="pdparam">mode</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>mode</code></em></span></dt><dd><p>

specifies how source and destination colors are combined.

It must be <code class="constant">GL_FUNC_ADD</code>, <code class="constant">GL_FUNC_SUBTRACT</code>,

<code class="constant">GL_FUNC_REVERSE_SUBTRACT</code>, <code class="constant">GL_MIN</code>, <code class="constant">GL_MAX</code>.

</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>

The blend equations determine how a new pixel (the ''source'' color)

is combined with a pixel already in the framebuffer (the ''destination''

color). This function sets both the RGB blend equation and the alpha

blend equation to a single equation.

</p><p>

These equations use the source and destination blend factors

specified by either <a class="citerefentry" href="glBlendFunc"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a> or

<a class="citerefentry" href="glBlendFuncSeparate"><span class="citerefentry"><span class="refentrytitle">glBlendFuncSeparate</span></span></a>.

See <a class="citerefentry" href="glBlendFunc"><span class="citerefentry"><span class="refentrytitle">glBlendFunc</span></span></a> or <a class="citerefentry" href="glBlendFuncSeparate"><span class="citerefentry"><span class="refentrytitle">glBlendFuncSeparate</span></span></a>

for a description of the various blend factors.

</p><p>

In the equations that follow, source and destination

color components are referred to as

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">s</mi>

</msub>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">s</mi>

</msub>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">s</mi>

</msub>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mfenced>

</math>

and

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">d</mi>

</msub>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">d</mi>

</msub>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">d</mi>

</msub>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mfenced>

</math>,

respectively.

The result color is referred to as

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">r</mi>

</msub>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">r</mi>

</msub>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">r</mi>

</msub>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">r</mi>

</msub>

</mfenced>

</math>.

The source and destination blend factors are denoted

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">R</mi>

</msub>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">G</mi>

</msub>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">B</mi>

</msub>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">A</mi>

</msub>

</mfenced>

</math>

and

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">R</mi>

</msub>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">G</mi>

</msub>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">B</mi>

</msub>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">A</mi>

</msub>

</mfenced>

</math>,

respectively.

For these equations all color components are understood to have values

in the range

<math overflow="scroll">

<mfenced open="[" close="]">

<mn>0</mn>

<mn>1</mn>

</mfenced>

</math>.

</p><div class="informaltable"><table><colgroup><col /><col /><col /></colgroup><thead><tr><th><span class="bold"><strong>

Mode

</strong></span></th><th><span class="bold"><strong>

RGB Components

</strong></span></th><th><span class="bold"><strong>

Alpha Component

</strong></span></th></tr></thead><tbody><tr><td>

<code class="constant">GL_FUNC_ADD</code>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Rr</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">R</mi>

</msub>

<mo>+</mo>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">R</mi>

</msub>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Gr</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">G</mi>

</msub>

<mo>+</mo>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">G</mi>

</msub>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Br</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">B</mi>

</msub>

<mo>+</mo>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">B</mi>

</msub>

</mrow>

</mrow>

</math></div>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Ar</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">A</mi>

</msub>

<mo>+</mo>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">A</mi>

</msub>

</mrow>

</mrow>

</math></div>

</td></tr><tr><td>

<code class="constant">GL_FUNC_SUBTRACT</code>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Rr</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">R</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">R</mi>

</msub>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Gr</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">G</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">G</mi>

</msub>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Br</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">B</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">B</mi>

</msub>

</mrow>

</mrow>

</math></div>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Ar</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">A</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">A</mi>

</msub>

</mrow>

</mrow>

</math></div>

</td></tr><tr><td>

<code class="constant">GL_FUNC_REVERSE_SUBTRACT</code>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Rr</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">R</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">R</mi>

</msub>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Gr</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">G</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">G</mi>

</msub>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Br</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">B</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">B</mi>

</msub>

</mrow>

</mrow>

</math></div>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Ar</mi>

<mo>=</mo>

<mrow>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">d</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">d</mi>

<mi mathvariant="italic">A</mi>

</msub>

<mo>-</mo>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">s</mi>

</msub>

<mo>⁢</mo>

<msub><mi mathvariant="italic">s</mi>

<mi mathvariant="italic">A</mi>

</msub>

</mrow>

</mrow>

</math></div>

</td></tr><tr><td>

<code class="constant">GL_MIN</code>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Rr</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">min</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Gr</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">min</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Br</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">min</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Ar</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">min</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

</td></tr><tr><td>

<code class="constant">GL_MAX</code>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Rr</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">max</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">R</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Gr</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">max</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">G</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Br</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">max</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">B</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

</td><td>

<div class="informalequation"><math overflow="scroll">

<mrow>

<mi mathvariant="italic">Ar</mi>

<mo>=</mo>

<mrow>

<mi mathvariant="italic">max</mi>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">s</mi>

</msub>

</mrow>

<mrow>

<msub><mi mathvariant="italic">A</mi>

<mi mathvariant="italic">d</mi>

</msub>

</mrow>

</mfenced>

</mrow>

</mrow>

</math></div>

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

</p><p>

The results of these equations are clamped to the range

<math overflow="scroll">

<mfenced open="[" close="]">

<mn>0</mn>

<mn>1</mn>

</mfenced>

</math>.

</p><p>

The <code class="constant">GL_MIN</code> and <code class="constant">GL_MAX</code> equations are useful for applications

that analyze image data (image thresholding against a constant color,

for example).

The <code class="constant">GL_FUNC_ADD</code> equation is useful

for antialiasing and transparency, among other things.

</p><p>

Initially, both the RGB blend equation and the alpha blend equation are set to <code class="constant">GL_FUNC_ADD</code>.

</p><p>

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>

The <code class="constant">GL_MIN</code>, and <code class="constant">GL_MAX</code> equations do not use

the source or destination factors, only the source and destination colors.

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>

<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>mode</code></em> is not one of

<code class="constant">GL_FUNC_ADD</code>, <code class="constant">GL_FUNC_SUBTRACT</code>, <code class="constant">GL_FUNC_REVERSE_SUBTRACT</code>,

<code class="constant">GL_MAX</code>, or <code class="constant">GL_MIN</code>.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glBlendEquation</code> is executed

between the execution of <a class="citerefentry" href="glBegin"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a> and the corresponding

execution of <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with an argument of <code class="constant">GL_BLEND_EQUATION_RGB</code>

</p><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with an argument of <code class="constant">GL_BLEND_EQUATION_ALPHA</code>

</p></div>

{$pipelinestall}{$examples}

<div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>

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

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

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

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

</p></div><div class="refsect1" lang="en" xml:lang="en"><div id="Copyright"><h2>Copyright</h2><p>

Copyright © 1991-2006

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

Free Software B License. For details, see

<a class="ulink" href="https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/" target="_top">https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/</a>.

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