132 lines
5.9 KiB
XML
132 lines
5.9 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="gluPickMatrix">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>gluPickMatrix</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>gluPickMatrix</refname>
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<refpurpose>define a picking region</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>gluPickMatrix</function></funcdef>
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<paramdef>GLdouble <parameter>x</parameter></paramdef>
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<paramdef>GLdouble <parameter>y</parameter></paramdef>
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<paramdef>GLdouble <parameter>delX</parameter></paramdef>
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<paramdef>GLdouble <parameter>delY</parameter></paramdef>
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<paramdef>GLint * <parameter>viewport</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>x</parameter></term>
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<term><parameter>y</parameter></term>
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<listitem>
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<para>
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Specify the center of a picking region in window coordinates.
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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>delX</parameter></term>
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<term><parameter>delY</parameter></term>
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<listitem>
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<para>
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Specify the width and height, respectively, of the picking region in window
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coordinates.
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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>viewport</parameter></term>
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<listitem>
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<para>
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Specifies the current viewport (as from a <citerefentry><refentrytitle>glGetIntegerv</refentrytitle></citerefentry> call).
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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>gluPickMatrix</function> creates a projection matrix that can be used to restrict drawing
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to a small region of the viewport.
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This is typically useful to
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determine what objects are being drawn near the cursor.
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Use <function>gluPickMatrix</function> to
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restrict drawing to a small region around the cursor.
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Then,
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enter selection mode (with <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry>) and rerender the scene.
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All primitives that would have been drawn near
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the cursor are identified and stored in the selection buffer.
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</para>
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<para>
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The matrix created by <function>gluPickMatrix</function> is multiplied by the current matrix just
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as if <citerefentry><refentrytitle>glMultMatrix</refentrytitle></citerefentry> is called with the generated matrix.
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To effectively use the generated pick matrix for picking,
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first call <citerefentry><refentrytitle>glLoadIdentity</refentrytitle></citerefentry> to load an identity matrix onto the
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perspective matrix stack.
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Then call <function>gluPickMatrix</function>,
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and, finally, call a command (such as <citerefentry><refentrytitle>gluPerspective</refentrytitle></citerefentry>)
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to multiply the perspective matrix by the pick matrix.
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</para>
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<para>
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When using <function>gluPickMatrix</function> to pick NURBS, be careful to turn off the NURBS
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property
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<constant>GLU_AUTO_LOAD_MATRIX</constant>. If <constant>GLU_AUTO_LOAD_MATRIX</constant> is not
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turned off, then any NURBS surface rendered is subdivided differently with
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the pick matrix than the way it was subdivided without the pick matrix.
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</para>
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</refsect1>
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<refsect1 id="example"><title>Example</title>
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<para>
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When rendering a scene as follows:
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<programlisting>
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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gluPerspective(...);
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glMatrixMode(GL_MODELVIEW);
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/* Draw the scene */
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</programlisting>
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a portion of the viewport can be selected as a pick region like this:
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<programlisting>
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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gluPickMatrix(x, y, width, height, viewport);
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gluPerspective(...);
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glMatrixMode(GL_MODELVIEW);
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/* Draw the scene */
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</programlisting>
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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>gluPerspective</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glLoadIdentity</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glMultMatrix</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glRenderMode</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> 1991-2006
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Silicon Graphics, Inc. This document is licensed under the SGI
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Free Software B License. For details, see
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<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
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</para>
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</refsect1>
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</refentry>
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