gl2/glBlendFunc.xhtml

<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 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" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            In RGBA mode, 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
            <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>.
            The color specified by <a class="citerefentry" 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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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">s</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>
                        </td><td>
                        <math overflow="scroll">

                            <mfenced open="(" close=")">
                                <msub><mi mathvariant="italic">A</mi>
                                <mi mathvariant="italic">c</mi>
                                </msub>
                                <msub><mi mathvariant="italic">A</mi>
                                <mi mathvariant="italic">c</mi>
                                </msub>
                                <msub><mi mathvariant="italic">A</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_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=")">
                                    <msub><mi mathvariant="italic">A</mi>
                                    <mi mathvariant="italic">c</mi>
                                    </msub>
                                    <msub><mi mathvariant="italic">A</mi>
                                    <mi mathvariant="italic">c</mi>
                                    </msub>
                                    <msub><mi mathvariant="italic">A</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_SRC_ALPHA_SATURATE</code>
                        </td><td>
                        <math overflow="scroll">

                            <mfenced open="(" close=")">
                                <mi mathvariant="italic">i</mi>
                                <mi mathvariant="italic">i</mi>
                                <mi mathvariant="italic">i</mi>
                                <mn>1</mn>
                            </mfenced>
                        </math>
                        </td></tr></tbody></table></div><p>
            In the table,
        </p><p>
            </p><p>
                <math overflow="scroll">

                    <mrow>
                        <mi mathvariant="italic">i</mi>
                        <mo>=</mo>
                        <mfrac>
                            <mrow>
                                <mi mathvariant="italic">min</mi>
                                <mo>⁡</mo>
                                <mfenced open="(" close=")">
                                    <msub><mi mathvariant="italic">A</mi>
                                    <mi mathvariant="italic">s</mi>
                                    </msub>
                                    <mrow>
                                        <msub><mi mathvariant="italic">k</mi>
                                        <mi mathvariant="italic">A</mi>
                                        </msub>
                                        <mo>-</mo>
                                        <msub><mi mathvariant="italic">A</mi>
                                        <mi mathvariant="italic">d</mi>
                                        </msub>
                                    </mrow>
                                </mfenced>
                            </mrow>
                            <msub><mi mathvariant="italic">k</mi>
                            <mi mathvariant="italic">A</mi>
                            </msub>
                        </mfrac>
                    </mrow>
                </math>
            </p><p>
        </p><p>
            To determine the blended RGBA values of a pixel when drawing in RGBA mode,
            the system uses the following equations:
        </p><p>
            </p><p>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">R</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <mrow>
                            <mi mathvariant="italic">min</mi>
                            <mo>⁡</mo>
                            <mfenced open="(" close=")">
                                <msub><mi mathvariant="italic">k</mi>
                                <mi mathvariant="italic">R</mi>
                                </msub>
                                <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>
                            </mfenced>
                        </mrow>
                    </mrow>
                </math>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">G</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <mrow>
                            <mi mathvariant="italic">min</mi>
                            <mo>⁡</mo>
                            <mfenced open="(" close=")">
                                <msub><mi mathvariant="italic">k</mi>
                                <mi mathvariant="italic">G</mi>
                                </msub>
                                <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>
                            </mfenced>
                        </mrow>
                    </mrow>
                </math>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">B</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <mrow>
                            <mi mathvariant="italic">min</mi>
                            <mo>⁡</mo>
                            <mfenced open="(" close=")">
                                <msub><mi mathvariant="italic">k</mi>
                                <mi mathvariant="italic">B</mi>
                                </msub>
                                <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>
                            </mfenced>
                        </mrow>
                    </mrow>
                </math>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">A</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <mrow>
                            <mi mathvariant="italic">min</mi>
                            <mo>⁡</mo>
                            <mfenced open="(" close=")">
                                <msub><mi mathvariant="italic">k</mi>
                                <mi mathvariant="italic">A</mi>
                                </msub>
                                <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>
                            </mfenced>
                        </mrow>
                    </mrow>
                </math>
            </p><p>
        </p><p>
            Despite the apparent precision of the above equations,
            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.
            For example,
            when <em class="parameter"><code>sfactor</code></em> is <code class="constant">GL_SRC_ALPHA</code>,
            <em class="parameter"><code>dfactor</code></em> is <code class="constant">GL_ONE_MINUS_SRC_ALPHA</code>,
            and
            <math overflow="scroll">

                <msub><mi mathvariant="italic">A</mi>
                <mi mathvariant="italic">s</mi>
                </msub>
            </math>
            is equal to
            <math overflow="scroll">

                <msub><mi mathvariant="italic">k</mi>
                <mi mathvariant="italic">A</mi>
                </msub>
            </math>,
            the equations reduce to simple replacement:
        </p><p>
            </p><p>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">R</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <msub><mi mathvariant="italic">R</mi>
                        <mi mathvariant="italic">s</mi>
                        </msub>
                    </mrow>
                </math>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">G</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <msub><mi mathvariant="italic">G</mi>
                        <mi mathvariant="italic">s</mi>
                        </msub>
                    </mrow>
                </math>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">B</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <msub><mi mathvariant="italic">B</mi>
                        <mi mathvariant="italic">s</mi>
                        </msub>
                    </mrow>
                </math>
                <math overflow="scroll">

                    <mrow>
                        <msub><mi mathvariant="italic">A</mi>
                        <mi mathvariant="italic">d</mi>
                        </msub>
                        <mo>=</mo>
                        <msub><mi mathvariant="italic">A</mi>
                        <mi mathvariant="italic">s</mi>
                        </msub>
                    </mrow>
                </math>
            </p><p>
        </p><p>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="examples"></a><h2>Examples</h2><p>
        </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><p>
            Blend function
            (<code class="constant">GL_SRC_ALPHA</code>, <code class="constant">GL_ONE_MINUS_SRC_ALPHA</code>)
            is also useful for rendering antialiased points and lines
            in arbitrary order.
        </p><p>
            Polygon antialiasing is optimized using blend function
            (<code class="constant">GL_SRC_ALPHA_SATURATE</code>, <code class="constant">GL_ONE</code>)
            with polygons sorted from nearest to farthest.
            (See the <a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>, <a class="citerefentry" href="glDisable"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> reference page and the
            <code class="constant">GL_POLYGON_SMOOTH</code> argument for information on polygon antialiasing.)
            Destination alpha bitplanes,
            which must be present for this blend function to operate correctly,
            store the accumulated coverage.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
            Incoming (source) alpha is correctly thought of as a material opacity,
            ranging from 1.0
            (<math overflow="scroll">

                <msub><mi mathvariant="italic">K</mi>
                <mi mathvariant="italic">A</mi>
                </msub>
            </math>),
            representing complete opacity,
            to 0.0 (0), representing complete
            transparency.
        </p><p>
            When more than one color buffer is enabled for drawing,
            the GL performs blending separately for each enabled buffer,
            using the contents of that buffer for destination color.
            (See <a class="citerefentry" href="glDrawBuffer"><span class="citerefentry"><span class="refentrytitle">glDrawBuffer</span></span></a>.)
        </p><p>
            Blending affects only RGBA rendering.
            It is ignored by color index renderers.
        </p><p>
            <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> are available only
            if the GL version is 1.4 or greater or if the <code class="code">ARB_imaging</code> is
            supported by your implementation.
        </p><p>
            <code class="constant">GL_SRC_COLOR</code> and <code class="constant">GL_ONE_MINUS_SRC_COLOR</code> are valid only for
            <em class="parameter"><code>sfactor</code></em> if the GL version is 1.4 or greater.
        </p><p>
            <code class="constant">GL_DST_COLOR</code> and <code class="constant">GL_ONE_MINUS_DST_COLOR</code> are valid only for
            <em class="parameter"><code>dfactor</code></em> if the GL version is 1.4 or greater.
        </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 either <em class="parameter"><code>sfactor</code></em> or <em class="parameter"><code>dfactor</code></em> is not an
            accepted value.
        </p><p>
            <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glBlendFunc</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 argument <code class="constant">GL_BLEND_SRC</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</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" lang="en" xml:lang="en"><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="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="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="glDrawBuffer"><span class="citerefentry"><span class="refentrytitle">glDrawBuffer</span></span></a>,
            <a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
            <a class="citerefentry" href="glLogicOp"><span class="citerefentry"><span class="refentrytitle">glLogicOp</span></span></a>,
            <a class="citerefentry" href="glStencilFunc"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</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>