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154 lines
7.1 KiB
XML
154 lines
7.1 KiB
XML
<?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="glDrawArraysInstancedBaseInstance">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>2010</year>
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<holder>Khronos Group</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glDrawArraysInstancedBaseInstance</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glDrawArraysInstancedBaseInstance</refname>
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<refpurpose>draw multiple instances of a range of elements with offset applied to instanced attributes</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>glDrawArraysInstancedBaseInstance</function></funcdef>
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<paramdef>GLenum <parameter>mode</parameter></paramdef>
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<paramdef>GLint <parameter>first</parameter></paramdef>
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<paramdef>GLsizei <parameter>count</parameter></paramdef>
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<paramdef>GLsizei <parameter>primcount</parameter></paramdef>
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<paramdef>GLuint <parameter>baseinstance</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>mode</parameter></term>
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<listitem>
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<para>
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Specifies what kind of primitives to render. Symbolic constants <constant>GL_POINTS</constant>,
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<constant>GL_LINE_STRIP</constant>, <constant>GL_LINE_LOOP</constant>, <constant>GL_LINES</constant>,
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<constant>GL_TRIANGLE_STRIP</constant>, <constant>GL_TRIANGLE_FAN</constant>, <constant>GL_TRIANGLES</constant>
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<constant>GL_LINES_ADJACENCY</constant>, <constant>GL_LINE_STRIP_ADJACENCY</constant>,
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<constant>GL_TRIANGLES_ADJACENCY</constant>, <constant>GL_TRIANGLE_STRIP_ADJACENCY</constant> and <constant>GL_PATCHES</constant>
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are accepted.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>first</parameter></term>
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<listitem>
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<para>
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Specifies the starting index in the enabled arrays.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>count</parameter></term>
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<listitem>
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<para>
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Specifies the number of indices to be rendered.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>primcount</parameter></term>
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<listitem>
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<para>
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Specifies the number of instances of the specified range of indices to be rendered.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>baseinstance</parameter></term>
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<listitem>
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<para>
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Specifies the base instance for use in fetching instanced vertex attributes.
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</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>
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<function>glDrawArraysInstancedBaseInstance</function> behaves identically to <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>
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except that <parameter>primcount</parameter> instances of the range of elements are executed and the value of the internal counter
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<parameter>instanceID</parameter> advances for each iteration. <parameter>instanceID</parameter> is an internal 32-bit integer counter
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that may be read by a vertex shader as <constant>gl_InstanceID</constant>.
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</para>
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<para>
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<function>glDrawArraysInstancedBaseInstance</function> has the same effect as:
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<programlisting><![CDATA[ if ( mode or count is invalid )
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generate appropriate error
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else {
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for (int i = 0; i < primcount ; i++) {
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instanceID = i;
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glDrawArrays(mode, first, count);
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}
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instanceID = 0;
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}]]></programlisting>
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</para>
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<para>
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Specific vertex attributes may be classified as <emphasis>instanced</emphasis> through the use of
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<citerefentry><refentrytitle>glVertexAttribDivisor</refentrytitle></citerefentry>. Instanced vertex attributes
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supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
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attribute arrays is calculated as:
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<mml:math>
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<mml:mrow>
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<mml:mfenced open = '⌊' close = '⌋'>
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<mml:mfrac>
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<mml:mrow>
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<mml:mi>gl</mml:mi>
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<mml:mo>_</mml:mo>
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<mml:mi>InstanceID</mml:mi>
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</mml:mrow>
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<mml:mi>divisor</mml:mi>
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</mml:mfrac>
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</mml:mfenced>
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<mml:mo lspace='2px' rspace='2px'>+</mml:mo>
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<mml:mi>baseInstance</mml:mi>
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</mml:mrow>
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</mml:math>. Note that <parameter>baseinstance</parameter> does not affect the shader-visible value of <constant>gl_InstanceID</constant>.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not one of
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the accepted values.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a geometry shader is active and <parameter>mode</parameter>
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is incompatible with the input primitive type of the geometry shader in the currently installed program object.
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</para>
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<para>
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<constant>GL_INVALID_VALUE</constant> is generated if <parameter>count</parameter> or <parameter>primcount</parameter> are negative.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
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enabled array and the buffer object's data store is currently mapped.
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>
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</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> 2011 Khronos Group.
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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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