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232 lines
9.8 KiB
XML
232 lines
9.8 KiB
XML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glGetActiveAttrib">
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<refmeta>
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<refentrytitle>glGetActiveAttrib</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glGetActiveAttrib</refname>
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<refpurpose>Returns information about an active attribute variable for the specified program object</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glGetActiveAttrib</function></funcdef>
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<paramdef>GLuint <parameter>program</parameter></paramdef>
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<paramdef>GLuint <parameter>index</parameter></paramdef>
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<paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
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<paramdef>GLsizei *<parameter>length</parameter></paramdef>
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<paramdef>GLint *<parameter>size</parameter></paramdef>
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<paramdef>GLenum *<parameter>type</parameter></paramdef>
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<paramdef>GLchar *<parameter>name</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>program</parameter></term>
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<listitem>
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<para>Specifies the program object to be
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queried.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>index</parameter></term>
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<listitem>
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<para>Specifies the index of the attribute variable
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to be queried.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>bufSize</parameter></term>
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<listitem>
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<para>Specifies the maximum number of characters
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OpenGL is allowed to write in the character buffer
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indicated by <parameter>name</parameter>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>length</parameter></term>
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<listitem>
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<para>Returns the number of characters actually
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written by OpenGL in the string indicated by
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<parameter>name</parameter> (excluding the null
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terminator) if a value other than
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<constant>NULL</constant> is passed.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>size</parameter></term>
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<listitem>
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<para>Returns the size of the attribute
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variable.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>type</parameter></term>
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<listitem>
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<para>Returns the data type of the attribute
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variable.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>name</parameter></term>
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<listitem>
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<para>Returns a null terminated string containing
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the name of the attribute variable.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para><function>glGetActiveAttrib</function> returns information
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about an active attribute variable in the program object
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specified by <parameter>program</parameter>. The number of
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active attributes can be obtained by calling
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<citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
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with the value <constant>GL_ACTIVE_ATTRIBUTES</constant>. A
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value of 0 for <parameter>index</parameter> selects the first
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active attribute variable. Permissible values for
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<parameter>index</parameter> range from 0 to the number of
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active attribute variables minus 1.</para>
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<para>A vertex shader may use either built-in attribute
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variables, user-defined attribute variables, or both. Built-in
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attribute variables have a prefix of "gl_" and
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reference conventional OpenGL vertex attribtes (e.g.,
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<parameter>gl_Vertex</parameter>,
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<parameter>gl_Normal</parameter>, etc., see the OpenGL Shading
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Language specification for a complete list.) User-defined
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attribute variables have arbitrary names and obtain their values
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through numbered generic vertex attributes. An attribute
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variable (either built-in or user-defined) is considered active
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if it is determined during the link operation that it may be
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accessed during program execution. Therefore,
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<parameter>program</parameter> should have previously been the
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target of a call to
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<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
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but it is not necessary for it to have been linked
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successfully.</para>
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<para>The size of the character buffer required to store the
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longest attribute variable name in
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<parameter>program</parameter> can be obtained by calling
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<citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
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with the value
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<constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>. This value
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should be used to allocate a buffer of sufficient size to store
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the returned attribute name. The size of this character buffer
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is passed in <parameter>bufSize</parameter>, and a pointer to
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this character buffer is passed in
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<parameter>name</parameter>.</para>
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<para><function>glGetActiveAttrib</function> returns the name of
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the attribute variable indicated by
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<parameter>index</parameter>, storing it in the character buffer
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specified by <parameter>name</parameter>. The string returned
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will be null terminated. The actual number of characters written
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into this buffer is returned in <parameter>length</parameter>,
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and this count does not include the null termination character.
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If the length of the returned string is not required, a value of
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<constant>NULL</constant> can be passed in the
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<parameter>length</parameter> argument.</para>
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<para>The <parameter>type</parameter> argument will return a
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pointer to the attribute variable's data type. The symbolic
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constants <constant>GL_FLOAT</constant>,
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<constant>GL_FLOAT_VEC2</constant>,
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<constant>GL_FLOAT_VEC3</constant>,
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<constant>GL_FLOAT_VEC4</constant>,
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<constant>GL_FLOAT_MAT2</constant>,
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<constant>GL_FLOAT_MAT3</constant>,
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<constant>GL_FLOAT_MAT4</constant>,
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<constant>GL_FLOAT_MAT2x3</constant>,
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<constant>GL_FLOAT_MAT2x4</constant>,
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<constant>GL_FLOAT_MAT3x2</constant>,
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<constant>GL_FLOAT_MAT3x4</constant>,
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<constant>GL_FLOAT_MAT4x2</constant>, or
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<constant>GL_FLOAT_MAT4x3</constant> may be returned. The
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<parameter>size</parameter> argument will return the size of the
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attribute, in units of the type returned in
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<parameter>type</parameter>.</para>
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<para>The list of active attribute variables may include both
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built-in attribute variables (which begin with the prefix
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"gl_") as well as user-defined attribute variable
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names.</para>
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<para>This function will return as much information as it can
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about the specified active attribute variable. If no information
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is available, <parameter>length</parameter> will be 0, and
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<parameter>name</parameter> will be an empty string. This
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situation could occur if this function is called after a link
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operation that failed. If an error occurs, the return values
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<parameter>length</parameter>, <parameter>size</parameter>,
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<parameter>type</parameter>, and <parameter>name</parameter>
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will be unmodified.</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para><function>glGetActiveAttrib</function>
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is available only if the GL version is 2.0 or greater.</para>
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<para><constant>GL_FLOAT_MAT2x3</constant>,
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<constant>GL_FLOAT_MAT2x4</constant>,
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<constant>GL_FLOAT_MAT3x2</constant>,
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<constant>GL_FLOAT_MAT3x4</constant>,
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<constant>GL_FLOAT_MAT4x2</constant>, and
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<constant>GL_FLOAT_MAT4x3</constant>
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will only be returned as a <parameter>type</parameter>
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if the GL version is 2.1 or greater.</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>program</parameter> is not a value generated by
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OpenGL.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if
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<parameter>program</parameter> is not a program object.</para>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>index</parameter> is greater than or equal to the
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number of active attribute variables in
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<parameter>program</parameter>.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if
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<function>glGetActiveAttrib</function> is executed between the
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execution of
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<citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
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and the corresponding execution of
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<citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</para>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>bufSize</parameter> is less than 0.</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with argument <constant>GL_MAX_VERTEX_ATTRIBS</constant>.</para>
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<para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
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with argument <constant>GL_ACTIVE_ATTRIBUTES</constant> or
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<constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>.</para>
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<para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para><citerefentry><refentrytitle>glBindAttribLocation</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glVertexAttrib</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glVertexAttribPointer</refentrytitle></citerefentry></para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 2003-2005 3Dlabs Inc. Ltd.
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This material may be distributed subject to the terms and conditions set forth in
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the Open Publication License, v 1.0, 8 June 1999.
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<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
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</para>
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</refsect1>
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</refentry>
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