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<refentry id="glTexEnv">
<refmeta>
<refentrytitle>glTexEnv</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refdescriptor>glTexEnv</refdescriptor>
<refname>glTexEnvf</refname>
<refname>glTexEnvx</refname>
<refname>glTexEnvfv</refname>
<refname>glTexEnvxv</refname>
<refpurpose>set texture environment parameters</refpurpose>
</refnamediv>
<refsynopsisdiv>
<title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glTexEnvf</function></funcdef>
<paramdef>GLenum <parameter>pname</parameter></paramdef>
<paramdef>GLfloat <parameter>param</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>glTexEnvx</function></funcdef>
<paramdef>GLenum <parameter>pname</parameter></paramdef>
<paramdef>GLfixed <parameter>param</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term>
<parameter>target</parameter>
</term>
<listitem>
<para>Specifies a texture environment. Must be
<constant>GL_TEXTURE_ENV</constant>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<parameter>pname</parameter>
</term>
<listitem>
<para>Specifies the symbolic name of a single-valued
texture environment parameter. Must be
<constant>GL_TEXTURE_ENV_MODE</constant>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<parameter>param</parameter>
</term>
<listitem>
<para>Specifies a single symbolic constant, one of
<constant>GL_MODULATE</constant>,
<constant>GL_DECAL</constant>,
<constant>GL_BLEND</constant>, or
<constant>GL_REPLACE</constant>.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsynopsisdiv>
<title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glTexEnvfv</function></funcdef>
<paramdef>GLenum <parameter>pname</parameter></paramdef>
<paramdef>const GLfloat * <parameter>params</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>glTexEnvxv</function></funcdef>
<paramdef>GLenum <parameter>pname</parameter></paramdef>
<paramdef>const GLfixed * <parameter>params</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term>
<parameter>target</parameter>
</term>
<listitem>
<para>Specifies a texture environment. Must be
<constant>GL_TEXTURE_ENV</constant>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<parameter>pname</parameter>
</term>
<listitem>
<para>Specifies the symbolic name of a texture
environment parameter. Accepted values are
<constant>GL_TEXTURE_ENV_MODE</constant> and
<constant>GL_TEXTURE_ENV_COLOR</constant>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<parameter>params</parameter>
</term>
<listitem>
<para>Specifies a pointer to a parameter array that
contains either a single symbolic constant or an RGBA
color.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>A texture environment specifies how texture values are
interpreted when a fragment is textured.
<parameter>target</parameter> must be
<constant>GL_TEXTURE_ENV</constant>.
<parameter>pname</parameter> can be either
<constant>GL_TEXTURE_ENV_MODE</constant> or
<constant>GL_TEXTURE_ENV_COLOR</constant>.</para>
<para>If <parameter>pname</parameter> is
<constant>GL_TEXTURE_ENV_MODE</constant>, then
<parameter>params</parameter>
is (or points to) the symbolic name of a texture function. Four
texture functions may be specified:
<constant>GL_MODULATE</constant>,
<constant>GL_DECAL</constant>,
<constant>GL_BLEND</constant>, and
<constant>GL_REPLACE</constant>.</para>
<para>A texture function acts on the fragment to be textured
using the texture image value that applies to the fragment (see
<citerefentry><refentrytitle>glTexParameter</refentrytitle></citerefentry>)
and produces an RGBA color for that fragment. The following
table shows how the RGBA color is produced for each of the
three texture functions that can be chosen.
<replaceable>C</replaceable> is a triple of color values (RGB) and
<replaceable>A</replaceable> is the associated alpha value.
RGBA values extracted from a texture image are in the range [0, 1].
The subscript <replaceable>f</replaceable> refers to the incoming fragment,
the subscript <replaceable>t</replaceable> to the texture image,
the subscript <replaceable>c</replaceable> to the texture environment color,
and subscript <replaceable>v</replaceable> indicates a value produced by
the texture function.</para>
<para>A texture image can have up to four components per
texture element (see
<citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry>,
and
<citerefentry><refentrytitle>glCopyTexImage2D</refentrytitle></citerefentry>).
In a one-component image, <inlineequation><math>
<msub><mi>L</mi><mi>t</mi></msub>
</math></inlineequation> indicates that single component.
A two-component image uses <inlineequation><math>
<msub><mi>L</mi><mi>t</mi></msub>
</math></inlineequation> and
<inlineequation><math>
<msub><mi>A</mi><mi>t</mi></msub>
</math></inlineequation>.
A three-component image has only a color value,
<inlineequation><math>
<msub><mi>C</mi><mi>t</mi></msub>
</math></inlineequation>.
A four-component image has both a color value
<inlineequation><math>
<msub><mi>C</mi><mi>t</mi></msub>
</math></inlineequation>
and an alpha value
<inlineequation><math>
<msub><mi>A</mi><mi>t</mi></msub>
</math></inlineequation>.</para>
<informaltable frame="none">
<tgroup cols="5" align="center">
<colspec colname="c1" align="left"/>
<colspec colname="c2" align="center"/>
<colspec colname="c3" align="center"/>
<colspec colname="c4" align="center"/>
<colspec colname="c5" align="center"/>
<spanspec spanname="texture functions" namest="c2" nameend="c3" align="center"/>
<thead>
<row>
<entry>Base internal</entry>
<entry spanname="texture functions">Texture functions</entry>
</row>
<row>
<entry>format</entry>
<entry><constant>GL_MODULATE</constant></entry>
<entry><constant>GL_DECAL</constant></entry>
</row>
</thead>
<tbody>
<row rowsep="1">
<entry><constant>GL_ALPHA</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>undefined</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry></entry>
</row>
<row rowsep="1">
<entry><constant>GL_LUMINANCE</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>L</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>undefined</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry></entry>
</row>
<row rowsep="1">
<entry><constant>GL_LUMINANCE_ALPHA</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>L</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>undefined</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry></entry>
</row>
<row rowsep="1">
<entry><constant>GL_RGB</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
</row>
<row rowsep="1">
<entry><constant>GL_RGBA</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<mfenced><mrow>
<mn>1</mn>
<mo>-</mo>
<msub><mi>A</mi><mi>t</mi></msub>
</mrow></mfenced>
<msub><mi>C</mi><mi>f</mi></msub>
<mo>+</mo>
<msub><mi>A</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<!-- second table -->
<informaltable frame="none">
<tgroup cols="3" align="center">
<colspec colname="c1" align="left"/>
<colspec colname="c2" align="center"/>
<colspec colname="c3" align="center"/>
<spanspec spanname="texture functions" namest="c2" nameend="c3" align="center"/>
<thead>
<row>
<entry>Base internal</entry>
<entry spanname="texture functions">Texture functions</entry>
</row>
<row>
<entry>format</entry>
<entry><constant>GL_BLEND</constant></entry>
<entry><constant>GL_REPLACE</constant></entry>
</row>
</thead>
<tbody>
<row rowsep="1">
<entry><constant>GL_ALPHA</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row rowsep="1">
<entry><constant>GL_LUMINANCE</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<mfenced><mrow>
<mn>1</mn>
<mo>-</mo>
<msub><mi>L</mi><mi>t</mi></msub>
</mrow></mfenced>
<msub><mi>C</mi><mi>f</mi></msub>
<mo>+</mo>
<msub><mi>L</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>c</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>L</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
</row>
<row rowsep="1">
<entry><constant>GL_LUMINANCE_ALPHA</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<mfenced><mrow>
<mn>1</mn>
<mo>-</mo>
<msub><mi>L</mi><mi>t</mi></msub>
</mrow></mfenced>
<msub><mi>C</mi><mi>f</mi></msub>
<mo>+</mo>
<msub><mi>L</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>c</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>L</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row rowsep="1">
<entry><constant>GL_RGB</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<mfenced><mrow>
<mn>1</mn>
<mo>-</mo>
<msub><mi>C</mi><mi>t</mi></msub>
</mrow></mfenced>
<msub><mi>C</mi><mi>f</mi></msub>
<mo>+</mo>
<msub><mi>C</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>c</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
</row>
<row rowsep="1">
<entry><constant>GL_RGBA</constant></entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<mfenced><mrow>
<mn>1</mn>
<mo>-</mo>
<msub><mi>C</mi><mi>t</mi></msub>
</mrow></mfenced>
<msub><mi>C</mi><mi>f</mi></msub>
<mo>+</mo>
<msub><mi>C</mi><mi>t</mi></msub>
<msub><mi>C</mi><mi>c</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>C</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>C</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
<row>
<entry></entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
<msub><mi>A</mi><mi>f</mi></msub>
</math></inlineequation>
</entry>
<entry>
<inlineequation><math>
<msub><mi>A</mi><mi>v</mi></msub>
<mo>=</mo>
<msub><mi>A</mi><mi>t</mi></msub>
</math></inlineequation>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>If <parameter>pname</parameter> is
<constant>GL_TEXTURE_ENV_COLOR</constant>,
<parameter>params</parameter>
is a pointer to an array that holds an RGBA color consisting of
four values. The values are clamped to the range [0, 1] when
they are specified.
<inlineequation><math>
<msub><mi>C</mi><mi>c</mi></msub>
</math></inlineequation>
takes these four values.</para>
<para>
The initial value of <constant>GL_TEXTURE_ENV_MODE</constant> is
<constant>GL_MODULATE</constant>. The initial value of
<constant>GL_TEXTURE_ENV_COLOR</constant> is (0, 0, 0, 0).</para>
</refsect1>
<refsect1>
<title>Errors</title>
<para><constant>GL_INVALID_ENUM</constant> is generated when
<parameter>target</parameter> or
<parameter>pname</parameter>
is not one of the accepted values, or when
<parameter>params</parameter>
should have a defined constant value (based on the value of
<parameter>pname</parameter>) and does not.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>glActiveTexture</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCompressedTexImage2D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCompressedTexSubImage2D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCopyTexImage2D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCopyTexSubImage2D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glTexParameter</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glTexSubImage2D</refentrytitle></citerefentry>
</para>
</refsect1>
</refentry>
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