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glBlendFunc.xhtml
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<div class="refentry"><a id="glBlendFunc"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glBlendFunc — specify pixel arithmetic</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <strong class="fsfunc">glBlendFunc</strong>(</code></td><td>GLenum <var class="pdparam">sfactor</var>, </td></tr><tr><td> </td><td>GLenum <var class="pdparam">dfactor</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>sfactor</code></em></span></dt><dd><p>
Specifies how the red, green, blue,
and alpha source blending factors are computed.
The following symbolic constants are accepted:
<code class="constant">GL_ZERO</code>,
<code class="constant">GL_ONE</code>,
<code class="constant">GL_SRC_COLOR</code>,
<code class="constant">GL_ONE_MINUS_SRC_COLOR</code>,
<code class="constant">GL_DST_COLOR</code>,
<code class="constant">GL_ONE_MINUS_DST_COLOR</code>,
<code class="constant">GL_SRC_ALPHA</code>,
<code class="constant">GL_ONE_MINUS_SRC_ALPHA</code>,
<code class="constant">GL_DST_ALPHA</code>,
<code class="constant">GL_ONE_MINUS_DST_ALPHA</code>,
<code class="constant">GL_CONSTANT_COLOR</code>,
<code class="constant">GL_ONE_MINUS_CONSTANT_COLOR</code>,
<code class="constant">GL_CONSTANT_ALPHA</code>,
<code class="constant">GL_ONE_MINUS_CONSTANT_ALPHA</code>, and
<code class="constant">GL_SRC_ALPHA_SATURATE</code>.
The initial value is <code class="constant">GL_ONE</code>.
</p></dd><dt><span class="term"><em class="parameter"><code>dfactor</code></em></span></dt><dd><p>
Specifies how the red, green, blue,
and alpha destination blending factors are computed.
The following symbolic constants are accepted:
<code class="constant">GL_ZERO</code>,
<code class="constant">GL_ONE</code>,
<code class="constant">GL_SRC_COLOR</code>,
<code class="constant">GL_ONE_MINUS_SRC_COLOR</code>,
<code class="constant">GL_DST_COLOR</code>,
<code class="constant">GL_ONE_MINUS_DST_COLOR</code>,
<code class="constant">GL_SRC_ALPHA</code>,
<code class="constant">GL_ONE_MINUS_SRC_ALPHA</code>,
<code class="constant">GL_DST_ALPHA</code>,
<code class="constant">GL_ONE_MINUS_DST_ALPHA</code>.
<code class="constant">GL_CONSTANT_COLOR</code>,
<code class="constant">GL_ONE_MINUS_CONSTANT_COLOR</code>,
<code class="constant">GL_CONSTANT_ALPHA</code>, and
<code class="constant">GL_ONE_MINUS_CONSTANT_ALPHA</code>.
The initial value is <code class="constant">GL_ZERO</code>.
</p></dd></dl></div></div><div class="refsect1"><a id="description"></a><h2>Description</h2><p>
Pixels can be drawn using a function that blends
the incoming (source) RGBA values with the RGBA values
that are already in the frame buffer (the destination values).
Blending is initially disabled.
Use <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_BLEND</code>
to enable and disable blending.
</p><p>
<code class="function">glBlendFunc</code> defines the operation of blending when it is enabled.
<em class="parameter"><code>sfactor</code></em> specifies which method is used to scale the
source color components.
<em class="parameter"><code>dfactor</code></em> specifies which method is used to scale the
destination color components.
The possible methods are described in the following table.
Each method defines four scale factors,
one each for red, green, blue, and alpha.
In the table and in subsequent equations, source and destination
color components are referred to as
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>
and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>.
The color specified by <a class="citerefentry" href="glBlendColor"><span class="citerefentry"><span class="refentrytitle">glBlendColor</span></span></a> is referred to as
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>.
They are understood to have integer values between 0 and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>,
where
</p><p>
</p><p>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:mo>=</mml:mo>
<mml:mrow>
<mml:msup><mml:mn>2</mml:mn>
<mml:mfenced open="" close="">
<mml:msub><mml:mi mathvariant="italic">m</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:msup>
<mml:mo>-</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mrow>
</mml:math>
</p><p>
</p><p>
and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">m</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">m</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">m</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">m</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>
is the number of red,
green,
blue,
and alpha bitplanes.
</p><p>
Source and destination scale factors are referred to as
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">s</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">s</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">s</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">s</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>
and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">d</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">d</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">d</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">d</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>.
The scale factors described in the table,
denoted
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>,
represent either source or destination factors.
All scale factors have range
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="[" close="]">
<mml:mn>0</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
</mml:math>.
</p><p>
</p><div class="informaltable"><table border="1"><colgroup><col align="left" /><col align="left" /></colgroup><thead><tr><th align="left"><span class="bold"><strong>
Parameter
</strong></span></th><th align="left"><span class="bold"><strong>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">f</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>
</strong></span></th></tr></thead><tbody><tr><td align="left">
<code class="constant">GL_ZERO</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:mn>0</mml:mn>
<mml:mn>0</mml:mn>
<mml:mn>0</mml:mn>
<mml:mn>0</mml:mn>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_ONE</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_SRC_COLOR</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_ONE_MINUS_SRC_COLOR</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
<mml:mo>-</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:mrow>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_DST_COLOR</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_ONE_MINUS_DST_COLOR</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
<mml:mo>-</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">R</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">G</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">B</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:mrow>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_SRC_ALPHA</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_ONE_MINUS_SRC_ALPHA</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
<mml:mo>-</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:mrow>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_DST_ALPHA</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_ONE_MINUS_DST_ALPHA</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
<mml:mo>-</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mfrac>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mfenced>
</mml:mrow>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_CONSTANT_COLOR</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_ONE_MINUS_CONSTANT_COLOR</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
<mml:mo>-</mml:mo>
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">R</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">G</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">B</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:mrow>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_CONSTANT_ALPHA</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_ONE_MINUS_CONSTANT_ALPHA</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mfenced open="(" close=")">
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
<mml:mn>1</mml:mn>
</mml:mfenced>
<mml:mo>-</mml:mo>
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">c</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:mrow>
</mml:math>
</td></tr><tr><td align="left">
<code class="constant">GL_SRC_ALPHA_SATURATE</code>
</td><td align="left">
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mfenced open="(" close=")">
<mml:mi mathvariant="italic">i</mml:mi>
<mml:mi mathvariant="italic">i</mml:mi>
<mml:mi mathvariant="italic">i</mml:mi>
<mml:mn>1</mml:mn>
</mml:mfenced>
</mml:math>
</td></tr></tbody></table></div><p>
In the table,
</p><p>
</p><p>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mi mathvariant="italic">i</mml:mi>
<mml:mo>=</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi mathvariant="italic">min</mml:mi>
<mml:mo></mml:mo>
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">s</mml:mi>
</mml:msub>
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
<mml:mo>-</mml:mo>
<mml:msub><mml:mi mathvariant="italic">A</mml:mi>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:msub><mml:mi mathvariant="italic">k</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:mfrac>
</mml:mrow>
</mml:math>
</p><p>
</p><p>
To determine the blended RGBA values of a pixel,
the system uses one of the equations set by
<a class="citerefentry" href="glBlendEquation"><span class="citerefentry"><span class="refentrytitle">glBlendEquation</span></span></a> or
<a class="citerefentry" href="glBlendEquationSeparate"><span class="citerefentry"><span class="refentrytitle">glBlendEquationSeparate</span></span></a>.
</p><p>
Blending arithmetic is not exactly specified,
because blending operates with imprecise integer color values.
However,
a blend factor that should be equal to 1
is guaranteed not to modify its multiplicand,
and a blend factor equal to 0 reduces its multiplicand to 0.
</p></div><div class="refsect1"><a id="notes"></a><h2>Notes</h2><p>
Incoming (source) alpha is correctly thought of as a material opacity,
ranging from 1.0
(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:msub><mml:mi mathvariant="italic">K</mml:mi>
<mml:mi mathvariant="italic">A</mml:mi>
</mml:msub>
</mml:math>),
representing complete opacity,
to 0.0 (0), representing complete
transparency.
</p><p>
Transparency is best implemented using blend function
(<code class="constant">GL_SRC_ALPHA</code>, <code class="constant">GL_ONE_MINUS_SRC_ALPHA</code>)
with primitives sorted from farthest to nearest.
Note that this transparency calculation does not require
the presence of alpha bitplanes in the frame buffer.
</p></div><div class="refsect1"><a id="errors"></a><h2>Errors</h2><p>
<code class="constant">GL_INVALID_ENUM</code> is generated if either <em class="parameter"><code>sfactor</code></em> or <em class="parameter"><code>dfactor</code></em> is not an
accepted value.
</p></div><div class="refsect1"><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 argument <code class="constant">GL_BLEND_SRC_RGB</code> or <code class="constant">GL_BLEND_SRC_ALPHA</code>
</p><p>
<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_BLEND_DST_RGB</code> or <code class="constant">GL_BLEND_DST_ALPHA</code>
</p><p>
<a class="citerefentry" href="glIsEnabled"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument <code class="constant">GL_BLEND</code>
</p><p>
</p></div>
{$pipelinestall}{$examples}
<div class="refsect1"><a id="seealso"></a><h2>See Also</h2><p>
<a class="citerefentry" href="glBlendColor"><span class="citerefentry"><span class="refentrytitle">glBlendColor</span></span></a>,
<a class="citerefentry" href="glBlendEquation"><span class="citerefentry"><span class="refentrytitle">glBlendEquation</span></span></a>,
<a class="citerefentry" href="glBlendEquationSeparate"><span class="citerefentry"><span class="refentrytitle">glBlendEquationSeparate</span></span></a>,
<a class="citerefentry" href="glBlendFuncSeparate"><span class="citerefentry"><span class="refentrytitle">glBlendFuncSeparate</span></span></a>,
<a class="citerefentry" href="glClear"><span class="citerefentry"><span class="refentrytitle">glClear</span></span></a>,
<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
<a class="citerefentry" href="glStencilFunc"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>
</p></div><div class="refsect1"><div id="Copyright"><h2>Copyright</h2><p>
Copyright <span class="trademark"></span>© 1991-2006
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>.
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