[clinton/guile-figl.git] / upstream-doc / man3 / glStencilOp.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
              "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="glStencilOp">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glStencilOp</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glStencilOp</refname>
        <refpurpose>set front and back stencil test actions</refpurpose>
    </refnamediv>
    <!-- eqn: ignoring delim $$ -->
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glStencilOp</function></funcdef>
                <paramdef>GLenum <parameter>sfail</parameter></paramdef>
                <paramdef>GLenum <parameter>dpfail</parameter></paramdef>
                <paramdef>GLenum <parameter>dppass</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>sfail</parameter></term>
            <listitem>
                <para>
                    Specifies the action to take when the stencil test fails.
                    Eight symbolic constants are accepted:
                    <constant>GL_KEEP</constant>,
                    <constant>GL_ZERO</constant>,
                    <constant>GL_REPLACE</constant>,
                    <constant>GL_INCR</constant>,
                    <constant>GL_INCR_WRAP</constant>,
                    <constant>GL_DECR</constant>,
                    <constant>GL_DECR_WRAP</constant>, and
                    <constant>GL_INVERT</constant>. The initial value is <constant>GL_KEEP</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>dpfail</parameter></term>
            <listitem>
                <para>
                    Specifies the stencil action when the stencil test passes,
                    but the depth test fails.
                    <parameter>dpfail</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
                    is <constant>GL_KEEP</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>dppass</parameter></term>
            <listitem>
                <para>
                    Specifies the stencil action when both the stencil test and the depth
                    test pass, or when the stencil test passes and either there is no
                    depth buffer or depth testing is not enabled.
                    <parameter>dppass</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
                    is <constant>GL_KEEP</constant>.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            Stenciling,
            like depth-buffering,
            enables and disables drawing on a per-pixel basis.
            You draw into the stencil planes using GL drawing primitives,
            then render geometry and images,
            using the stencil planes to mask out portions of the screen.
            Stenciling is typically used in multipass rendering algorithms
            to achieve special effects,
            such as decals,
            outlining,
            and constructive solid geometry rendering.
        </para>
        <para>
            The stencil test conditionally eliminates a pixel based on the outcome
            of a comparison between the value in the stencil buffer and a
            reference value. To enable and disable the test, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>
            and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument
            <constant>GL_STENCIL_TEST</constant>; to control it, call 
            <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> or 
            <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>.
        </para>
        <para>
            There can be two separate sets of <parameter>sfail</parameter>, <parameter>dpfail</parameter>, and 
            <parameter>dppass</parameter> parameters; one affects back-facing polygons, and the other
            affects front-facing polygons as well as other non-polygon primitives. 
            <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> sets both front
            and back stencil state to the same values. Use <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>
            to set front and back stencil state to different values.
        </para>
        <para>
            <function>glStencilOp</function> takes three arguments that indicate what happens
            to the stored stencil value while stenciling is enabled.
            If the stencil test fails,
            no change is made to the pixel's color or depth buffers,
            and <parameter>sfail</parameter> specifies what happens to the stencil buffer contents.
            The following eight actions are possible.
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GL_KEEP</constant></term>
                <listitem>
                    <para>
                        Keeps the current value.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_ZERO</constant></term>
                <listitem>
                    <para>
                        Sets the stencil buffer value to 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_REPLACE</constant></term>
                <listitem>
                    <para>
                        Sets the stencil buffer value to <emphasis>ref</emphasis>,
                        as specified by <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_INCR</constant></term>
                <listitem>
                    <para>
                        Increments the current stencil buffer value.
                        Clamps to the maximum representable unsigned value.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_INCR_WRAP</constant></term>
                <listitem>
                    <para>
                        Increments the current stencil buffer value.
                        Wraps stencil buffer value to zero when incrementing the maximum
                        representable unsigned value.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_DECR</constant></term>
                <listitem>
                    <para>
                        Decrements the current stencil buffer value.
                        Clamps to 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_DECR_WRAP</constant></term>
                <listitem>
                    <para>
                        Decrements the current stencil buffer value.
                        Wraps stencil buffer value to the maximum representable unsigned value when
                        decrementing a stencil buffer value of zero.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_INVERT</constant></term>
                <listitem>
                    <para>
                        Bitwise inverts the current stencil buffer value.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
        <para>
            Stencil buffer values are treated as unsigned integers.
            When incremented and decremented,
            values are clamped to 0 and 
            <inlineequation><mml:math>
                <!-- eqn: 2 sup n - 1: -->
                <mml:mrow>
                    <mml:msup><mml:mn>2</mml:mn>
                    <mml:mi mathvariant="italic">n</mml:mi>
                    </mml:msup>
                    <mml:mo>-</mml:mo>
                    <mml:mn>1</mml:mn>
                </mml:mrow>
            </mml:math></inlineequation>,
            where 
            <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
            is the value returned by querying <constant>GL_STENCIL_BITS</constant>.
        </para>
        <para>
            The other two arguments to <function>glStencilOp</function> specify stencil buffer actions
            that depend on whether subsequent depth buffer tests succeed (<parameter>dppass</parameter>)
            or fail (<parameter>dpfail</parameter>) (see
            <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>).
            The actions are specified using the same eight symbolic constants as <parameter>sfail</parameter>.
            Note that <parameter>dpfail</parameter> is ignored when there is no depth buffer,
            or when the depth buffer is not enabled.
            In these cases, <parameter>sfail</parameter> and <parameter>dppass</parameter> specify stencil action when the
            stencil test fails and passes,
            respectively.
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            Initially the stencil test is disabled.
            If there is no stencil buffer,
            no stencil modification can occur
            and it is as if the stencil tests always pass,
            regardless of any call to <function>glStencilOp</function>.
        </para>
        <para>
            <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> is the same as
            calling <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>
            with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>sfail</parameter>,
            <parameter>dpfail</parameter>, or <parameter>dppass</parameter> is any value other than the defined constant values.
        </para>
    </refsect1>
    <refsect1 id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument 
            <constant>GL_STENCIL_FAIL</constant>, <constant>GL_STENCIL_PASS_DEPTH_PASS</constant>, 
            <constant>GL_STENCIL_PASS_DEPTH_FAIL</constant>, <constant>GL_STENCIL_BACK_FAIL</constant>, 
            <constant>GL_STENCIL_BACK_PASS_DEPTH_PASS</constant>, <constant>GL_STENCIL_BACK_PASS_DEPTH_FAIL</constant>,
            or <constant>GL_STENCIL_BITS</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_TEST</constant>
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glStencilOpSeparate</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>
Commit	Line	Data
7faf1d71 AW	1	<?xml version="1.0" encoding="UTF-8"?>
	2	<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
	3	"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
	4	<refentry id="glStencilOp">
	5	<refmeta>
	6	<refmetainfo>
	7	<copyright>
	8	<year>1991-2006</year>
	9	<holder>Silicon Graphics, Inc.</holder>
	10	</copyright>
	11	</refmetainfo>
	12	<refentrytitle>glStencilOp</refentrytitle>
	13	<manvolnum>3G</manvolnum>
	14	</refmeta>
	15	<refnamediv>
	16	<refname>glStencilOp</refname>
	17	<refpurpose>set front and back stencil test actions</refpurpose>
	18	</refnamediv>
	19	<!-- eqn: ignoring delim $$ -->
	20	<refsynopsisdiv><title>C Specification</title>
	21	<funcsynopsis>
	22	<funcprototype>
	23	<funcdef>void <function>glStencilOp</function></funcdef>
	24	<paramdef>GLenum <parameter>sfail</parameter></paramdef>
	25	<paramdef>GLenum <parameter>dpfail</parameter></paramdef>
	26	<paramdef>GLenum <parameter>dppass</parameter></paramdef>
	27	</funcprototype>
	28	</funcsynopsis>
	29	</refsynopsisdiv>
	30	<refsect1 id="parameters"><title>Parameters</title>
	31	<variablelist>
	32	<varlistentry>
	33	<term><parameter>sfail</parameter></term>
	34	<listitem>
	35	<para>
	36	Specifies the action to take when the stencil test fails.
	37	Eight symbolic constants are accepted:
	38	<constant>GL_KEEP</constant>,
	39	<constant>GL_ZERO</constant>,
	40	<constant>GL_REPLACE</constant>,
	41	<constant>GL_INCR</constant>,
	42	<constant>GL_INCR_WRAP</constant>,
	43	<constant>GL_DECR</constant>,
	44	<constant>GL_DECR_WRAP</constant>, and
	45	<constant>GL_INVERT</constant>. The initial value is <constant>GL_KEEP</constant>.
	46	</para>
	47	</listitem>
	48	</varlistentry>
	49	<varlistentry>
	50	<term><parameter>dpfail</parameter></term>
	51	<listitem>
	52	<para>
	53	Specifies the stencil action when the stencil test passes,
	54	but the depth test fails.
	55	<parameter>dpfail</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
	56	is <constant>GL_KEEP</constant>.
	57	</para>
	58	</listitem>
	59	</varlistentry>
	60	<varlistentry>
	61	<term><parameter>dppass</parameter></term>
	62	<listitem>
	63	<para>
	64	Specifies the stencil action when both the stencil test and the depth
65	test pass, or when the stencil test passes and either there is no
66	depth buffer or depth testing is not enabled.
67	<parameter>dppass</parameter> accepts the same symbolic constants as <parameter>sfail</parameter>. The initial value
68	is <constant>GL_KEEP</constant>.
69	</para>
70	</listitem>
71	</varlistentry>
72	</variablelist>
73	</refsect1>
74	<refsect1 id="description"><title>Description</title>
75	<para>
76	Stenciling,
77	like depth-buffering,
78	enables and disables drawing on a per-pixel basis.
79	You draw into the stencil planes using GL drawing primitives,
80	then render geometry and images,
81	using the stencil planes to mask out portions of the screen.
82	Stenciling is typically used in multipass rendering algorithms
83	to achieve special effects,
84	such as decals,
85	outlining,
86	and constructive solid geometry rendering.
87	</para>
88	<para>
89	The stencil test conditionally eliminates a pixel based on the outcome
90	of a comparison between the value in the stencil buffer and a
91	reference value. To enable and disable the test, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>
92	and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument
93	<constant>GL_STENCIL_TEST</constant>; to control it, call
94	<citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> or
95	<citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>.
96	</para>
97	<para>
98	There can be two separate sets of <parameter>sfail</parameter>, <parameter>dpfail</parameter>, and
99	<parameter>dppass</parameter> parameters; one affects back-facing polygons, and the other
100	affects front-facing polygons as well as other non-polygon primitives.
101	<citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> sets both front
102	and back stencil state to the same values. Use <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>
103	to set front and back stencil state to different values.
104	</para>
105	<para>
106	<function>glStencilOp</function> takes three arguments that indicate what happens
107	to the stored stencil value while stenciling is enabled.
108	If the stencil test fails,
109	no change is made to the pixel's color or depth buffers,
110	and <parameter>sfail</parameter> specifies what happens to the stencil buffer contents.
111	The following eight actions are possible.
112	</para>
113	<variablelist>
114	<varlistentry>
115	<term><constant>GL_KEEP</constant></term>
116	<listitem>
117	<para>
118	Keeps the current value.
119	</para>
120	</listitem>
121	</varlistentry>
122	<varlistentry>
123	<term><constant>GL_ZERO</constant></term>
124	<listitem>
125	<para>
126	Sets the stencil buffer value to 0.
127	</para>
128	</listitem>
129	</varlistentry>
130	<varlistentry>
131	<term><constant>GL_REPLACE</constant></term>
132	<listitem>
133	<para>
134	Sets the stencil buffer value to <emphasis>ref</emphasis>,
135	as specified by <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>.
136	</para>
137	</listitem>
138	</varlistentry>
139	<varlistentry>
140	<term><constant>GL_INCR</constant></term>
141	<listitem>
142	<para>
143	Increments the current stencil buffer value.
144	Clamps to the maximum representable unsigned value.
145	</para>
146	</listitem>
147	</varlistentry>
148	<varlistentry>
149	<term><constant>GL_INCR_WRAP</constant></term>
150	<listitem>
151	<para>
152	Increments the current stencil buffer value.
153	Wraps stencil buffer value to zero when incrementing the maximum
154	representable unsigned value.
155	</para>
156	</listitem>
157	</varlistentry>
158	<varlistentry>
159	<term><constant>GL_DECR</constant></term>
160	<listitem>
161	<para>
162	Decrements the current stencil buffer value.
163	Clamps to 0.
164	</para>
165	</listitem>
166	</varlistentry>
167	<varlistentry>
168	<term><constant>GL_DECR_WRAP</constant></term>
169	<listitem>
170	<para>
171	Decrements the current stencil buffer value.
172	Wraps stencil buffer value to the maximum representable unsigned value when
173	decrementing a stencil buffer value of zero.
174	</para>
175	</listitem>
176	</varlistentry>
177	<varlistentry>
178	<term><constant>GL_INVERT</constant></term>
179	<listitem>
180	<para>
181	Bitwise inverts the current stencil buffer value.
182	</para>
183	</listitem>
184	</varlistentry>
185	</variablelist>
186	<para>
187	Stencil buffer values are treated as unsigned integers.
188	When incremented and decremented,
189	values are clamped to 0 and
190	<inlineequation><mml:math>
191	<!-- eqn: 2 sup n - 1: -->
192	<mml:mrow>
193	<mml:msup><mml:mn>2</mml:mn>
194	<mml:mi mathvariant="italic">n</mml:mi>
195	</mml:msup>
196	<mml:mo>-</mml:mo>
197	<mml:mn>1</mml:mn>
198	</mml:mrow>
199	</mml:math></inlineequation>,
200	where
201	<inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
202	is the value returned by querying <constant>GL_STENCIL_BITS</constant>.
203	</para>
204	<para>
205	The other two arguments to <function>glStencilOp</function> specify stencil buffer actions
206	that depend on whether subsequent depth buffer tests succeed (<parameter>dppass</parameter>)
207	or fail (<parameter>dpfail</parameter>) (see
208	<citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>).
209	The actions are specified using the same eight symbolic constants as <parameter>sfail</parameter>.
210	Note that <parameter>dpfail</parameter> is ignored when there is no depth buffer,
211	or when the depth buffer is not enabled.
212	In these cases, <parameter>sfail</parameter> and <parameter>dppass</parameter> specify stencil action when the
213	stencil test fails and passes,
214	respectively.
215	</para>
216	</refsect1>
217	<refsect1 id="notes"><title>Notes</title>
218	<para>
219	Initially the stencil test is disabled.
220	If there is no stencil buffer,
221	no stencil modification can occur
222	and it is as if the stencil tests always pass,
223	regardless of any call to <function>glStencilOp</function>.
224	</para>
225	<para>
226	<citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry> is the same as
227	calling <citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>
228	with <parameter>face</parameter> set to <constant>GL_FRONT_AND_BACK</constant>.
229	</para>
230	</refsect1>
231	<refsect1 id="errors"><title>Errors</title>
232	<para>
233	<constant>GL_INVALID_ENUM</constant> is generated if <parameter>sfail</parameter>,
234	<parameter>dpfail</parameter>, or <parameter>dppass</parameter> is any value other than the defined constant values.
235	</para>
236	</refsect1>
237	<refsect1 id="associatedgets"><title>Associated Gets</title>
238	<para>
239	<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument
240	<constant>GL_STENCIL_FAIL</constant>, <constant>GL_STENCIL_PASS_DEPTH_PASS</constant>,
241	<constant>GL_STENCIL_PASS_DEPTH_FAIL</constant>, <constant>GL_STENCIL_BACK_FAIL</constant>,
242	<constant>GL_STENCIL_BACK_PASS_DEPTH_PASS</constant>, <constant>GL_STENCIL_BACK_PASS_DEPTH_FAIL</constant>,
243	or <constant>GL_STENCIL_BITS</constant>
244	</para>
245	<para>
246	<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_STENCIL_TEST</constant>
247	</para>
248	</refsect1>
249	<refsect1 id="seealso"><title>See Also</title>
250	<para>
251	<citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
252	<citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
253	<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
254	<citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
255	<citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>,
256	<citerefentry><refentrytitle>glStencilFuncSeparate</refentrytitle></citerefentry>,
257	<citerefentry><refentrytitle>glStencilMask</refentrytitle></citerefentry>,
258	<citerefentry><refentrytitle>glStencilMaskSeparate</refentrytitle></citerefentry>,
259	<citerefentry><refentrytitle>glStencilOpSeparate</refentrytitle></citerefentry>
260	</para>
261	</refsect1>
262	<refsect1 id="Copyright"><title>Copyright</title>
263	<para>
264	Copyright <trademark class="copyright"></trademark> 1991-2006
265	Silicon Graphics, Inc. This document is licensed under the SGI
266	Free Software B License. For details, see
267	<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
268	</para>
269	</refsect1>
270	</refentry>