<div class="refentry" lang="en" xml:lang="en"><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><tr><td><code class="funcdef">void <b class="fsfunc">glBlendFunc</b>(</code></td><td>GLenum  </td><td><var class="pdparam">sfactor</var>, </td></tr><tr><td> </td><td>GLenum  </td><td><var class="pdparam">dfactor</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>sfactor</code></em></span></dt><dd><p>

Specifies how the red, green, blue,

and alpha source blending factors are computed.

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" lang="en" xml:lang="en"><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 href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and <a 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.

Both parameters must be one of the following symbolic constants:

<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>,

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

<code class="constant">GL_SRC1_COLOR</code>,

<code class="constant">GL_ONE_MINUS_SRC1_COLOR</code>,

<code class="constant">GL_SRC1_ALPHA</code>, and

<code class="constant">GL_ONE_MINUS_SRC1_ALPHA</code>.

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, first source, second source

and destination color components are referred to as

<math overflow="scroll">

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

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

<mi mathvariant="italic">s0</mi>

</msub>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

<mi mathvariant="italic">s0</mi>

</msub>

</mfenced>

</math>,

<math overflow="scroll">

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

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

<mi mathvariant="italic">s1</mi>

</msub>

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

<mi mathvariant="italic">s1</mi>

</msub>

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

<mi mathvariant="italic">s1</mi>

</msub>

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

<mi mathvariant="italic">s1</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 color specified by <a href="glBlendColor"><span class="citerefentry"><span class="refentrytitle">glBlendColor</span></span></a> is referred to as

<math overflow="scroll">

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

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

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

</msub>

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

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

</msub>

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

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

</msub>

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

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

</msub>

</mfenced>

</math>.

They are understood to have integer values between 0 and

<math overflow="scroll">

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

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

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

</msub>

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

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

</msub>

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

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

</msub>

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

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

</msub>

</mfenced>

</math>,

where

</p><p>

</p><p>

<math overflow="scroll">

<mrow>

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

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

</msub>

<mo>=</mo>

<mrow>

<msup><mn>2</mn>

<mfenced open="" close="">

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

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

</msub>

</mfenced>

</msup>

<mo>-</mo>

<mn>1</mn>

</mrow>

</mrow>

</math>

</p><p>

</p><p>

and

<math overflow="scroll">

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

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

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

</msub>

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

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

</msub>

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

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

</msub>

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

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

</msub>

</mfenced>

</math>

is the number of red,

green,

blue,

and alpha bitplanes.

</p><p>

Source and destination scale factors are referred to as

<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>.

The scale factors described in the table,

denoted

<math overflow="scroll">

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

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

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

</msub>

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

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

</msub>

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

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

</msub>

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

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

</msub>

</mfenced>

</math>,

represent either source or destination factors.

All scale factors have range

<math overflow="scroll">

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

<mn>0</mn>

<mn>1</mn>

</mfenced>

</math>.

</p><p>

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

Parameter

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

<math overflow="scroll">

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

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

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

</msub>

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

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

</msub>

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

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

</msub>

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

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

</msub>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

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

<mn>0</mn>

<mn>0</mn>

<mn>0</mn>

<mn>0</mn>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

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

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

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

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

<mrow>

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

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

</mfenced>

<mo>-</mo>

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

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</mrow>

</math>

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

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

</td><td>

<math overflow="scroll">

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

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

<mrow>

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

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

</mfenced>

<mo>-</mo>

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

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</mrow>

</math>

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

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

</td><td>

<math overflow="scroll">

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

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

<mrow>

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

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

</mfenced>

<mo>-</mo>

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

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

<mi mathvariant="italic">s0</mi>

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</mrow>

</math>

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

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

</td><td>

<math overflow="scroll">

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

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

<mrow>

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

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

</mfenced>

<mo>-</mo>

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

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

<mfrac>

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

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

</msub>

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

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

</msub>

</mfrac>

</mfenced>

</mrow>

</math>

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

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

</td><td>

<math overflow="scroll">

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

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

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

</msub>

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

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

</msub>

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

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

</msub>

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

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

</msub>

</mfenced>

</math>

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

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

</td><td>

<math overflow="scroll">

<mrow>

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

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

<mn>1</mn>

</mfenced>

<mo>-</mo>

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

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

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

</msub>

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

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

</msub>

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

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

</msub>

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

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

</msub>

</mfenced>

</mrow>

</math>

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

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