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<span id="Render-Settings"></span><div class="header">
<p>
Next: <a href="Rendering-Engine.html" accesskey="n" rel="next">Rendering Engine</a>, Previous: <a href="Viewports.html" accesskey="p" rel="prev">Viewports</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p>
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<hr />
<span id="Render-Settings-1"></span><h4 class="subsection">5.3.16 Render Settings</h4>
<span id="Blending"></span><h4 class="subsubsection">5.3.16.1 Blending</h4>
<p>Rendering a scene often involves drawing layers of objects that
overlap each other. Blending determines how two overlapping pixels
are combined in the final image that is rendered to the screen. The
<code>(chickadee graphics blend)</code> module provides a data type for
blending modes.
</p>
<p>Chickadee provides the following blend modes:
</p>
<dl>
<dt id="index-blend_003aalpha">Variable: <strong>blend:alpha</strong></dt>
<dd><p>Blend pixels according to the values of their alpha channels. This is
the most commonly used blend mode.
</p></dd></dl>
<dl>
<dt id="index-blend_003areplace">Variable: <strong>blend:replace</strong></dt>
<dd><p>Overwrite the output pixel color with the color being drawn.
</p></dd></dl>
<dl>
<dt id="index-blend_003aadd">Variable: <strong>blend:add</strong></dt>
<dd><p>Add all pixel color values together. The more colors blended
together, the more white the final color becomes.
</p></dd></dl>
<dl>
<dt id="index-blend_003asubtract">Variable: <strong>blend:subtract</strong></dt>
<dd><p>Subtract all pixel color values. The more colors blended together,
the more black the final color becomes.
</p></dd></dl>
<dl>
<dt id="index-blend_003amultiply">Variable: <strong>blend:multiply</strong></dt>
</dl>
<dl>
<dt id="index-blend_003adarken">Variable: <strong>blend:darken</strong></dt>
</dl>
<dl>
<dt id="index-blend_003alighten">Variable: <strong>blend:lighten</strong></dt>
</dl>
<dl>
<dt id="index-blend_003ascreen">Variable: <strong>blend:screen</strong></dt>
</dl>
<p>Custom blend modes can be created using the <code>make-blend-mode</code> procedure:
</p>
<dl>
<dt id="index-make_002dblend_002dmode">Procedure: <strong>make-blend-mode</strong> <em>equation source-function destination-function</em></dt>
<dd><p>Return a new custom blend mode that applies <var>source-function</var> to
the source color, <var>destination-function</var> to the destination color,
and finally applies <var>equation</var> to the transformed
source/destination color values. These arguments are <em>not</em>
procedures, but symbolic representations of the functions that OpenGL
supports.
</p>
<p>Valid values for <var>equation</var> are:
</p>
<ul>
<li> <code>add</code>
</li><li> <code>subtract</code>
</li><li> <code>reverse-subtract</code>
</li><li> <code>min</code>
</li><li> <code>max</code>
</li><li> <code>alpha-min</code>
</li><li> <code>alpha-max</code>
</li></ul>
<p>Valid values for <var>source-function</var> are:
</p>
<ul>
<li> <code>zero</code>
</li><li> <code>one</code>
</li><li> <code>destination-color</code>
</li><li> <code>one-minus-destination-color</code>
</li><li> <code>source-alpha-saturate</code>
</li><li> <code>source-alpha</code>
</li><li> <code>one-minus-source-alpha</code>
</li><li> <code>destination-alpha</code>
</li><li> <code>one-minus-destination-alpha</code>
</li><li> <code>constant-color</code>
</li><li> <code>one-minus-constant-color</code>
</li><li> <code>constant-alpha</code>
</li><li> <code>one-minus-constant-alpha</code>
</li></ul>
<p>Valid values for <var>destination-function</var> are:
</p>
<ul>
<li> <code>zero</code>
</li><li> <code>one</code>
</li><li> <code>source-color</code>
</li><li> <code>one-minus-source-color</code>
</li><li> <code>source-alpha</code>
</li><li> <code>one-minus-source-alpha</code>
</li><li> <code>destination-alpha</code>
</li><li> <code>one-minus-destination-alpha</code>
</li><li> <code>constant-color</code>
</li><li> <code>one-minus-constant-color</code>
</li><li> <code>constant-alpha</code>
</li><li> <code>one-minus-constant-alpha</code>
</li></ul>
</dd></dl>
<span id="Polygon-Modes-and-Culling"></span><h4 class="subsubsection">5.3.16.2 Polygon Modes and Culling</h4>
<p>The <code>(chickadee graphics polygon)</code> module provides access to the
<code>g:polygon-mode</code> and <code>g:cull-face-mode</code> render states.
</p>
<dl>
<dt id="index-fill_002dpolygon_002dmode">Variable: <strong>fill-polygon-mode</strong></dt>
<dd><p>Completely fill in the polygon. This is the default mode.
</p></dd></dl>
<dl>
<dt id="index-line_002dpolygon_002dmode">Variable: <strong>line-polygon-mode</strong></dt>
<dd><p>Render only the edges of the polygon. Produces a wireframe.
</p></dd></dl>
<dl>
<dt id="index-point_002dpolygon_002dmode">Variable: <strong>point-polygon-mode</strong></dt>
<dd><p>Render only the vertex positions as points.
</p></dd></dl>
<dl>
<dt id="index-make_002dpolygon_002dmode">Procedure: <strong>make-polygon-mode</strong> <em>front back</em></dt>
<dd><p>Return a new polygon mode that uses the method <var>front</var> for the
front face and <var>back</var> for the back face. The valid modes are
<code>fill</code>, <code>line</code>, and <var>point</var>.
</p></dd></dl>
<dl>
<dt id="index-polygon_002dmode_003f">Procedure: <strong>polygon-mode?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a polygon mode.
</p></dd></dl>
<dl>
<dt id="index-current_002dpolygon_002dmode">Procedure: <strong>current-polygon-mode</strong></dt>
<dd><p>Return the current polygon mode.
</p></dd></dl>
<dl>
<dt id="index-g_003apolygon_002dmode">Variable: <strong>g:polygon-mode</strong></dt>
<dd><p>Render state for polygon modes (see <a href="Rendering-Engine.html">Rendering Engine</a>.)
</p></dd></dl>
<dl>
<dt id="index-no_002dcull_002dface_002dmode">Variable: <strong>no-cull-face-mode</strong></dt>
<dd><p>Don’t cull any faces.
</p></dd></dl>
<dl>
<dt id="index-back_002dcull_002dface_002dmode">Variable: <strong>back-cull-face-mode</strong></dt>
<dd><p>Cull only back faces.
</p></dd></dl>
<dl>
<dt id="index-front_002dcull_002dface_002dmode">Variable: <strong>front-cull-face-mode</strong></dt>
<dd><p>Cull only front faces.
</p></dd></dl>
<dl>
<dt id="index-front_002dand_002dback_002dcull_002dface_002dmode">Variable: <strong>front-and-back-cull-face-mode</strong></dt>
<dd><p>Cull both front and back faces.
</p></dd></dl>
<dl>
<dt id="index-cull_002dface_002dmode_003f">Procedure: <strong>cull-face-mode?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a cull face mode.
</p></dd></dl>
<dl>
<dt id="index-cull_002dface_002dmode_002dfront_003f">Procedure: <strong>cull-face-mode-front?</strong> <em>cull-face-mode</em></dt>
<dd><p>Return <code>#t</code> if <var>cull-face-mode</var> culls front faces.
</p></dd></dl>
<dl>
<dt id="index-cull_002dface_002dmode_002dback_003f">Procedure: <strong>cull-face-mode-back?</strong> <em>cull-face-mode</em></dt>
<dd><p>Return <code>#t</code> if <var>cull-face-mode</var> culls back faces.
</p></dd></dl>
<dl>
<dt id="index-current_002dcull_002dface_002dmode">Procedure: <strong>current-cull-face-mode</strong></dt>
<dd><p>Return the current cull face mode.
</p></dd></dl>
<dl>
<dt id="index-g_003acull_002dface_002dmode">Variable: <strong>g:cull-face-mode</strong></dt>
<dd><p>Render state for cull face modes (see <a href="Rendering-Engine.html">Rendering Engine</a>.)
</p></dd></dl>
<span id="Depth-Testing"></span><h4 class="subsubsection">5.3.16.3 Depth Testing</h4>
<p>The <code>(chickadee graphics depth)</code> module provides access to the
<code>g:depth-test</code> render state.
</p>
<dl>
<dt id="index-make_002ddepth_002dtest">Procedure: <strong>make-depth-test</strong> <em>[#:write? #t] [#:function 'less-than] [#:near 0.0] [#:far 1.0]</em></dt>
<dd>
<p>Return a new depth test object. If <var>write</var> is <code>#t</code>, the
depth buffer will be written to during a draw call. <var>near</var> and
<var>far</var> define the min/max Z values for which depth testing may
pass.
</p>
<p><var>function</var> specifies how the depth value of pixel being drawn
compares to the depth value that is already in the depth buffer. When
this comparison is true, the depth test passes and the pixel is drawn.
When it fails, the pixel is discarded.
</p>
<p>The possible values of <var>function</var> are:
</p>
<ul>
<li> <code>always</code>
</li><li> <code>never</code>
</li><li> <code>equal</code>
</li><li> <code>not-equal</code>
</li><li> <code>less-than</code>
</li><li> <code>less-than-or-equal</code>
</li><li> <code>greater-than</code>
</li><li> <code>greater-than-or-equal</code>
</li></ul>
</dd></dl>
<dl>
<dt id="index-depth_002dtest_003f">Procedure: <strong>depth-test?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> when <var>obj</var> is a depth test object.
</p></dd></dl>
<dl>
<dt id="index-depth_002dtest_002dwrite_003f">Procedure: <strong>depth-test-write?</strong> <em>depth-test</em></dt>
<dd><p>Return <code>#t</code> when <var>depth-test</var> will write to the depth buffer.
</p></dd></dl>
<dl>
<dt id="index-depth_002dtest_002dfunction">Procedure: <strong>depth-test-function</strong> <em>depth-test</em></dt>
<dd><p>Return the comparison function of <var>depth-test</var>.
</p></dd></dl>
<dl>
<dt id="index-depth_002dtest_002dnear">Procedure: <strong>depth-test-near</strong> <em>depth-test</em></dt>
<dd><p>Return the near Z value of <var>depth-test</var>.
</p></dd></dl>
<dl>
<dt id="index-depth_002dtest_002dfar">Procedure: <strong>depth-test-far</strong> <em>depth-test</em></dt>
<dd><p>Return the far Z value of <var>depth-test</var>.
</p></dd></dl>
<dl>
<dt id="index-current_002ddepth_002dtest">Procedure: <strong>current-depth-test</strong></dt>
<dd><p>Return the current depth test.
</p></dd></dl>
<dl>
<dt id="index-g_003adepth_002dtest">Variable: <strong>g:depth-test</strong></dt>
<dd><p>Render state for depth tests (see <a href="Rendering-Engine.html">Rendering Engine</a>.)
</p></dd></dl>
<span id="Stencil-Testing"></span><h4 class="subsubsection">5.3.16.4 Stencil Testing</h4>
<p>The <code>(chickadee graphics stencil)</code> module provides access to the
<code>g:stencil-test</code> render state.
</p>
<dl>
<dt id="index-default_002dstencil_002dtest">Variable: <strong>default-stencil-test</strong></dt>
<dd><p>A stencil test that always passes.
</p></dd></dl>
<dl>
<dt id="index-make_002dstencil_002dtest">Procedure: <strong>make-stencil-test</strong> <em>[#:mask #xFF] [#:function always] [#:function-mask #xFF] [#:reference 0] [#:on-fail keep] [#:on-depth-fail keep] [#:on-pass keep] [#:mask-front mask] [#:mask-back mask] [#:function-mask-front function-mask] [#:function-mask-back function-mask] [#:refrence-front reference] [#:reference-back reference] [#:on-fail-front on-fail] [#:on-fail-back on-fail] [#:on-depth-fail-front on-depth-fail] [#:on-depth-fail-back on-depth-fail] [#:on-pass-front on-pass] [#:on-pass-back on-pass]</em></dt>
<dd>
<p>Return a new stencil test object. Different configurations can be
used for the front and back faces by using the arguments that end in
“front” or “back”.
</p>
<p>Valid values for <var>on-pass</var>, <var>on-fail</var>, and <var>on-depth-fail</var>
are:
</p>
<ul>
<li> <code>zero</code>
</li><li> <code>keep</code>
</li><li> <code>replace</code>
</li><li> <code>increment</code>
</li><li> <code>increment-wrap</code>
</li><li> <code>decrement</code>
</li><li> <code>decrement-wrap</code>
</li><li> <code>invert</code>
</li></ul>
<p>Valid values for <var>function</var> are:
</p>
<ul>
<li> <code>always</code>
</li><li> <code>never</code>
</li><li> <code>equal</code>
</li><li> <code>not-equal</code>
</li><li> <code>less-than</code>
</li><li> <code>less-than-or-equal</code>
</li><li> <code>greater-than</code>
</li><li> <code>greater-than-or-equal</code>
</li></ul>
</dd></dl>
<dl>
<dt id="index-stencil_002dtest_003f">Procedure: <strong>stencil-test?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> when <var>obj</var> is a stencil test object.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dmask_002dfront">Procedure: <strong>stencil-test-mask-front</strong> <em>stencil-test</em></dt>
<dd><p>Return the front mask of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dmask_002dback">Procedure: <strong>stencil-test-mask-back</strong> <em>stencil-test</em></dt>
<dd><p>Return the back mask of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dfunction_002dfront">Procedure: <strong>stencil-test-function-front</strong> <em>stencil-test</em></dt>
<dd><p>Return the front function of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dfunction_002dback">Procedure: <strong>stencil-test-function-back</strong> <em>stencil-test</em></dt>
<dd><p>Return the back function of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dfunction_002dmask_002dfront">Procedure: <strong>stencil-test-function-mask-front</strong> <em>stencil-test</em></dt>
<dd><p>Return the front function-mask of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dfunction_002dmask_002dback">Procedure: <strong>stencil-test-function-mask-back</strong> <em>stencil-test</em></dt>
<dd><p>Return the back function-mask of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dreference_002dfront">Procedure: <strong>stencil-test-reference-front</strong> <em>stencil-test</em></dt>
<dd><p>Return the front reference value of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002dreference_002dback">Procedure: <strong>stencil-test-reference-back</strong> <em>stencil-test</em></dt>
<dd><p>Return the back reference value of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002don_002dfail_002dfront">Procedure: <strong>stencil-test-on-fail-front</strong> <em>stencil-test</em></dt>
<dd><p>Return the front failure action of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002don_002dfail_002dback">Procedure: <strong>stencil-test-on-fail-back</strong> <em>stencil-test</em></dt>
<dd><p>Return the back failure action of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002don_002ddepth_002dfail_002dfront">Procedure: <strong>stencil-test-on-depth-fail-front</strong> <em>stencil-test</em></dt>
<dd><p>Return the front depth test failure action of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002don_002ddepth_002dfail_002dback">Procedure: <strong>stencil-test-on-depth-fail-back</strong> <em>stencil-test</em></dt>
<dd><p>Return the back depth test failure action of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002don_002dpass_002dfront">Procedure: <strong>stencil-test-on-pass-front</strong> <em>stencil-test</em></dt>
<dd><p>Return the front pass action of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-stencil_002dtest_002don_002dpass_002dback">Procedure: <strong>stencil-test-on-pass-back</strong> <em>stencil-test</em></dt>
<dd><p>Return the back pass action of <var>stencil-test</var>.
</p></dd></dl>
<dl>
<dt id="index-current_002dstencil_002dtest">Procedure: <strong>current-stencil-test</strong></dt>
<dd><p>Return the current stencil test.
</p></dd></dl>
<dl>
<dt id="index-g_003astencil_002dtest">Variable: <strong>g:stencil-test</strong></dt>
<dd><p>Render state for stencil testing (see <a href="Rendering-Engine.html">Rendering Engine</a>.)
</p></dd></dl>
<span id="Multisample-Antialiasing"></span><h4 class="subsubsection">5.3.16.5 Multisample Antialiasing</h4>
<p>Multisample antialiasing is a feature supported by many, but not all,
graphics cards. It is a nice easy way to improve the final frame that
the user sees, particularly in 3D scenes. The <code>(chickadee
graphics multisample)</code> module provides access to the
<code>g:multisample?</code> render state.
</p>
<dl>
<dt id="index-current_002dmultisample">Procedure: <strong>current-multisample</strong></dt>
<dd><p>Return <code>#t</code> if multisampling is enabled.
</p></dd></dl>
<dl>
<dt id="index-g_003amultisample_003f">Variable: <strong>g:multisample?</strong></dt>
<dd><p>Render state for multisampling (see <a href="Rendering-Engine.html">Rendering Engine</a>.)
</p></dd></dl>
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