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176 lines
8.8 KiB
XML
176 lines
8.8 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="glDrawElementsInstancedBaseVertexBaseInstance">
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<refentryinfo>
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<copyright>
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<year>2011-2013</year>
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<holder>Khronos Group</holder>
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</copyright>
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</refentryinfo>
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<refmeta>
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<refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glDrawElementsInstancedBaseVertexBaseInstance</refname>
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<refpurpose>render multiple instances of a set of primitives from array data with a per-element offset</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>glDrawElementsInstancedBaseVertexBaseInstance</function></funcdef>
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<paramdef>GLenum <parameter>mode</parameter></paramdef>
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<paramdef>GLsizei <parameter>count</parameter></paramdef>
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<paramdef>GLenum <parameter>type</parameter></paramdef>
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<paramdef>GLvoid *<parameter>indices</parameter></paramdef>
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<paramdef>GLsizei <parameter>primcount</parameter></paramdef>
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<paramdef>GLint <parameter>basevertex</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.
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Symbolic constants
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<constant>GL_POINTS</constant>, <constant>GL_LINE_STRIP</constant>, <constant>GL_LINE_LOOP</constant>,
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<constant>GL_LINES</constant>, <constant>GL_TRIANGLE_STRIP</constant>, <constant>GL_TRIANGLE_FAN</constant>,
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<constant>GL_TRIANGLES</constant>, <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> 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>count</parameter></term>
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<listitem>
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<para>
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Specifies the number of elements 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>type</parameter></term>
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<listitem>
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<para>
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Specifies the type of the values in indices. Must be one of <constant>GL_UNSIGNED_BYTE</constant>,
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<constant>GL_UNSIGNED_SHORT</constant>, or <constant>GL_UNSIGNED_INT</constant>.
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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>indices</parameter></term>
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<listitem>
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<para>
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Specifies a pointer to the location where the indices are stored.
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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 indexed geometry that should be drawn.
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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>basevertex</parameter></term>
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<listitem>
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<para>
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Specifies a constant that should be added to each element of <parameter>indices</parameter>
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when chosing elements from the enabled vertex 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>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>glDrawElementsInstancedBaseVertexBaseInstance</function> behaves identically to
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<citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry> except that the <emphasis>i</emphasis>th element
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transferred by the corresponding draw call will be taken from element <parameter>indices</parameter>[i] + <parameter>basevertex</parameter>
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of each enabled array. If the resulting value is larger than the maximum value representable by <parameter>type</parameter>,
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it is as if the calculation were upconverted to 32-bit unsigned integers (with wrapping on overflow conditions).
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The operation is undefined if the sum would be negative. The <parameter>basevertex</parameter> has no effect on the
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shader-visible value of <constant>gl_VertexID</constant>.
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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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<inlineequation>
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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>
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</inlineequation>. Note that <parameter>baseinstance</parameter>
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does not affect the shader-visible value of
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<constant>gl_InstanceID</constant>.
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</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>
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<function>glDrawElementsInstancedBaseVertex</function> is only supported if the GL version is 3.2 or greater.
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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 an accepted value.
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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> is negative.
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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_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
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enabled array or the element 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>glDrawElements</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawRangeElements</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawRangeElementsBaseVertex</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawElementsInstancedBaseVertex</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> 2011-2013 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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