Opentk/Source/Bind/Specifications/Docs/GL/glDrawArraysInstancedBaseInstance.xml

<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>

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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glDrawArraysInstancedBaseInstance">
    <info>
        <copyright>
            <year>2011-2013</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glDrawArraysInstancedBaseInstance</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glDrawArraysInstancedBaseInstance</refname>
        <refpurpose>draw multiple instances of a range of elements with offset applied to instanced attributes</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glDrawArraysInstancedBaseInstance</function></funcdef>
                <paramdef>GLenum <parameter>mode</parameter></paramdef>
                <paramdef>GLint <parameter>first</parameter></paramdef>
                <paramdef>GLsizei <parameter>count</parameter></paramdef>
                <paramdef>GLsizei <parameter>primcount</parameter></paramdef>
                <paramdef>GLuint <parameter>baseinstance</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>mode</parameter></term>
            <listitem>
                <para>
                    Specifies what kind of primitives to render. Symbolic constants <constant>GL_POINTS</constant>,
                    <constant>GL_LINE_STRIP</constant>, <constant>GL_LINE_LOOP</constant>, <constant>GL_LINES</constant>,
                    <constant>GL_TRIANGLE_STRIP</constant>, <constant>GL_TRIANGLE_FAN</constant>, <constant>GL_TRIANGLES</constant>
                    <constant>GL_LINES_ADJACENCY</constant>, <constant>GL_LINE_STRIP_ADJACENCY</constant>,
                    <constant>GL_TRIANGLES_ADJACENCY</constant>, <constant>GL_TRIANGLE_STRIP_ADJACENCY</constant> and <constant>GL_PATCHES</constant>
                    are accepted.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>first</parameter></term>
            <listitem>
                <para>
                    Specifies the starting index in the enabled arrays.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>count</parameter></term>
            <listitem>
                <para>
                    Specifies the number of indices to be rendered.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>primcount</parameter></term>
            <listitem>
                <para>
                    Specifies the number of instances of the specified range of indices to be rendered.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>baseinstance</parameter></term>
            <listitem>
                <para>
                    Specifies the base instance for use in fetching instanced vertex attributes.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            <function>glDrawArraysInstancedBaseInstance</function> behaves identically to <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>
            except that <parameter>primcount</parameter> instances of the range of elements are executed and the value of the internal counter
            <parameter>instanceID</parameter> advances for each iteration. <parameter>instanceID</parameter> is an internal 32-bit integer counter
            that may be read by a vertex shader as <constant>gl_InstanceID</constant>.
        </para>
        <para>
            <function>glDrawArraysInstancedBaseInstance</function> has the same effect as:
            <programlisting>    if ( mode or count is invalid )
        generate appropriate error
    else {
        for (int i = 0; i &lt; primcount ; i++) {
            instanceID = i;
            glDrawArrays(mode, first, count);
        }
        instanceID = 0;
    }</programlisting>
        </para>
        <para>
            Specific vertex attributes may be classified as <emphasis>instanced</emphasis> through the use of
            <citerefentry><refentrytitle>glVertexAttribDivisor</refentrytitle></citerefentry>. Instanced vertex attributes
            supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
            attribute arrays is calculated as:
            <inlineequation>
                <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                  <mml:mrow>
                    <mml:mfenced open="&lfloor;" close="&rfloor;">
                      <mml:mfrac>
                        <mml:mrow>
                          <mml:mi>gl</mml:mi>
                          <mml:mo>_</mml:mo>
                          <mml:mi>InstanceID</mml:mi>
                        </mml:mrow>
                        <mml:mi>divisor</mml:mi>
                      </mml:mfrac>
                    </mml:mfenced>
                    <mml:mo lspace="2px" rspace="2px">&plus;</mml:mo>
                    <mml:mi>baseInstance</mml:mi>
                  </mml:mrow>
                </mml:math>
            </inlineequation>. Note that <parameter>baseinstance</parameter>
            does not affect the shader-visible value of
            <constant>gl_InstanceID</constant>.
        </para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not one of
            the accepted values.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if a geometry shader is active and <parameter>mode</parameter>
            is incompatible with the input primitive type of the geometry shader in the currently installed program object.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>count</parameter> or <parameter>primcount</parameter> are negative.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
            enabled array and the buffer object's data store is currently mapped.
        </para>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2011-2013 Khronos Group.
            This material may be distributed subject to the terms and conditions set forth in
            the Open Publication License, v 1.0, 8 June 1999.
            <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
        </para>
    </refsect1>
</refentry>