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212 lines
10 KiB
XML
212 lines
10 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="glMultiDrawElementsIndirect">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>2012</year>
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<holder>Khronos Group.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glMultiDrawElementsIndirect</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glMultiDrawElementsIndirect</refname>
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<refpurpose>render indexed primitives from array data, taking parameters from memory</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>glMultiDrawElementsIndirect</function></funcdef>
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<paramdef>GLenum <parameter>mode</parameter></paramdef>
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<paramdef>GLenum <parameter>type</parameter></paramdef>
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<paramdef>const void *<parameter>indirect</parameter></paramdef>
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<paramdef>GLsizei <parameter>drawcount</parameter></paramdef>
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<paramdef>GLsizei <parameter>stride</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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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>,
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<constant>GL_LINE_STRIP</constant>,
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<constant>GL_LINE_LOOP</constant>,
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<constant>GL_LINES</constant>,
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<constant>GL_LINE_STRIP_ADJACENCY</constant>,
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<constant>GL_LINES_ADJACENCY</constant>,
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<constant>GL_TRIANGLE_STRIP</constant>,
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<constant>GL_TRIANGLE_FAN</constant>,
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<constant>GL_TRIANGLES</constant>,
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<constant>GL_TRIANGLE_STRIP_ADJACENCY</constant>,
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<constant>GL_TRIANGLES_ADJACENCY</constant>, and
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<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>type</parameter></term>
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<listitem>
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<para>
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Specifies the type of data in the buffer bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding.
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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>indirect</parameter></term>
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<listitem>
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<para>
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Specifies the address of a structure containing an array of draw parameters.
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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>drawcount</parameter></term>
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<listitem>
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<para>
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Specifies the number of elements in the array addressed by <parameter>indirect</parameter>.
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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>stride</parameter></term>
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<listitem>
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<para>
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Specifies the distance in basic machine units between elements of the draw parameter array.
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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>glMultiDrawElementsIndirect</function> specifies multiple indexed geometric primitives
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with very few subroutine calls. <function>glMultiDrawElementsIndirect</function> behaves
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similarly to a multitude of calls to <citerefentry><refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle></citerefentry>,
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execpt that the parameters to <citerefentry><refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle></citerefentry>
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are stored in an array in memory at the address given by <parameter>indirect</parameter>, separated
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by the stride, in basic machine units, specified by <parameter>stride</parameter>. If <parameter>stride</parameter>
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is zero, then the array is assumed to be tightly packed in memory.
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</para>
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<para>
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The parameters addressed by <parameter>indirect</parameter> are packed into a structure
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that takes the form (in C):
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<programlisting><![CDATA[ typedef struct {
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uint count;
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uint instanceCount;
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uint firstIndex;
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uint baseVertex;
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uint baseInstance;
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} DrawElementsIndirectCommand;]]></programlisting>
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</para>
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<para>
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A single call to <function>glMultiDrawElementsIndirect</function> is equivalent, assuming no errors
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are generated to:
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<programlisting><![CDATA[ GLsizei n;
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for (n = 0; n < drawcount; n++)
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{
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const DrawElementsIndirectCommand *cmd;
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if (stride != 0)
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{
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cmd = (const DrawElementsIndirectCommand *)((uintptr)indirect + n * stride);
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}
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else
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{
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cmd = (const DrawElementsIndirectCommand *)indirect + n;
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}
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glDrawElementsInstancedBaseVertexBaseInstance(mode,
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cmd->count,
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type,
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cmd->firstIndex + size-of-type,
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cmd->instanceCount,
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cmd->baseVertex,
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cmd->baseInstance);
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}]]></programlisting>
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</para>
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<para>
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If a buffer is bound to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding at the time
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of a call to <function>glDrawElementsIndirect</function>, <parameter>indirect</parameter>
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is interpreted as an offset, in basic machine units, into that buffer and the parameter
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data is read from the buffer rather than from client memory.
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</para>
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<para>
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Note that indices stored in client memory are not supported. If no buffer is bound to the
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<constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding, an error will be generated.
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</para>
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<para>
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The results of the operation are undefined if the <code>reservedMustBeZero</code> member
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of the parameter structure is non-zero. However, no error is generated in this case.
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</para>
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<para>
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Vertex attributes that are modified by <function>glDrawElementsIndirect</function> have an
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unspecified value after <function>glDrawElementsIndirect</function> returns. Attributes that aren't
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modified remain well defined.
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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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The <parameter>baseInstance</parameter> member of the <parameter>DrawElementsIndirectCommand</parameter>
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structure is defined only if the GL version is 4.2 or greater. For versions of the GL less than 4.2,
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this parameter is present but is reserved and should be set to zero. On earlier versions of the GL,
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behavior is undefined if it is non-zero.
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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>stride</parameter> is not a multiple
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of four.
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</para>
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<para>
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<constant>GL_INVALID_VALUE</constant> is generated if <parameter>drawcount</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 no buffer is bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant>
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binding, or if such a buffer's data store is currently mapped.
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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 to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding and the buffer object's data store is currently mapped.
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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 <parameter>mode</parameter> is <constant>GL_PATCHES</constant>
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and no tessellation control shader is active.
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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>glDrawArraysInstanced</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawArraysIndirect</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawRangeElements</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawElementsIndirect</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glMultiDrawArraysIndirect</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> 2010-2013 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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