
<refentry id="glLineStipple">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glLineStipple</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glLineStipple</refname>
        <refpurpose>specify the line stipple pattern</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glLineStipple</function></funcdef>
                <paramdef>GLint <parameter>factor</parameter></paramdef>
                <paramdef>GLushort <parameter>pattern</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <!-- eqn: ignoring delim $$ -->
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>factor</parameter></term>
            <listitem>
                <para>
                    Specifies a multiplier for each bit in the line stipple pattern.
                    If <parameter>factor</parameter> is 3,
                    for example,
                    each bit in the pattern is used three times
                    before the next bit in the pattern is used.
                    <parameter>factor</parameter> is clamped to the range [1, 256] and defaults to 1.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>pattern</parameter></term>
            <listitem>
                <para>
                    Specifies a 16-bit integer whose bit pattern determines
                    which fragments of a line will be drawn when the line is rasterized.
                    Bit zero is used first; the default pattern is all 1's.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            Line stippling masks out certain fragments produced by rasterization;
            those fragments will not be drawn.
            The masking is achieved by using three parameters:
            the 16-bit line stipple pattern <parameter>pattern</parameter>,
            the repeat count <parameter>factor</parameter>,
            and an integer stipple counter 
            <inlineequation><mml:math><mml:mi mathvariant="italic">s</mml:mi></mml:math></inlineequation>.
        </para>
        <para>
            Counter 
            <inlineequation><mml:math><mml:mi mathvariant="italic">s</mml:mi></mml:math></inlineequation>
            is reset to 0 whenever <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> is called
            and before each line segment of a <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>(<constant>GL_LINES</constant>)/<citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>
            sequence is generated.
            It is incremented after each fragment of a unit width aliased line segment
            is generated
            or after each 
            <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
            fragments of an 
            <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
            width line segment are generated.
            The 
            <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
            fragments associated with count 
            <inlineequation><mml:math><mml:mi mathvariant="italic">s</mml:mi></mml:math></inlineequation>
            are masked out if
        </para>
        <para>
            <parameter>pattern</parameter> bit 
            <inlineequation><mml:math>
                <!-- eqn: (s  /  factor)  mod  16:-->
                <mml:mrow>
                    <mml:mfenced open="(" close=")">
                        <mml:mfrac>
                            <mml:mi mathvariant="italic">s</mml:mi>
                            <mml:mi mathvariant="italic">factor</mml:mi>
                        </mml:mfrac>
                    </mml:mfenced>
                    <mml:mo>%</mml:mo>
                    <mml:mn>16</mml:mn>
                </mml:mrow>
            </mml:math></inlineequation>
        </para>
        <para>
            is 0, otherwise these fragments are sent to the frame buffer.
            Bit zero of <parameter>pattern</parameter> is the least significant bit.
        </para>
        <para>
            Antialiased lines are treated as a sequence of 
            <inlineequation><mml:math>
                <!-- eqn: 1 times width:-->
                <mml:mrow>
                    <mml:mn>1</mml:mn>
                    <mml:mo>&times;</mml:mo>
                    <mml:mi mathvariant="italic">width</mml:mi>
                </mml:mrow>
            </mml:math></inlineequation>
            rectangles
            for purposes of stippling.
            Whether rectangle 
            <inlineequation><mml:math><mml:mi mathvariant="italic">s</mml:mi></mml:math></inlineequation>
            is rasterized or not depends on the fragment rule
            described for aliased lines,
            counting rectangles rather than groups of fragments.
        </para>
        <para>
            To enable and disable line stippling, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>
            with argument <constant>GL_LINE_STIPPLE</constant>.
            When enabled,
            the line stipple pattern is applied as described above.
            When disabled,
            it is as if the pattern were all 1's.
            Initially, line stippling is disabled.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glLineStipple</function>
            is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
            and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
        </para>
    </refsect1>
    <refsect1 id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LINE_STIPPLE_PATTERN</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LINE_STIPPLE_REPEAT</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_LINE_STIPPLE</constant>
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glLineWidth</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glPolygonStipple</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
        </para>
    </refsect1>
</refentry>
