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* Chickadee: (chickadee). Game programming toolkit for Guile.
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<title>Rendering Engine (The Chickadee Game Toolkit)</title>
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<p>
Next: <a href="Buffers.html#Buffers" accesskey="n" rel="next">Buffers</a>, Previous: <a href="Viewports.html#Viewports" accesskey="p" rel="prev">Viewports</a>, Up: <a href="Graphics.html#Graphics" accesskey="u" rel="up">Graphics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html#Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Rendering-Engine-1"></a>
<h4 class="subsection">2.3.10 Rendering Engine</h4>
<p>Chickadee defines rendering using a metaphor familiar to Scheme
programmers: procedure application. A shader (see <a href="Shaders.html#Shaders">Shaders</a>) is
like a procedure for the GPU to apply. Shaders are passed arguments:
A vertex array containing the geometry to render (see <a href="Buffers.html#Buffers">Buffers</a>) and
zero or more keyword arguments that the shader understands. Similar
to how Scheme has <code>apply</code> for calling procedures, Chickadee
provides <code>gpu-apply</code> for calling shaders.
</p>
<p>Additionally, there is some dynamic state that effects how
<code>gpu-apply</code> will behave. Things like the current viewport,
framebuffer, and blend mode are stored as dynamic state because it
would be tedious to have to have to specify them each time
<code>gpu-apply</code> is called.
</p>
<p>The following procedures and syntax can be found in the
<code>(chickadee render)</code> module.
</p>
<dl>
<dt><a name="index-gpu_002dapply"></a>Syntax: <strong>gpu-apply</strong> <em>shader vertex-array [#:uniform-key uniform-value …]</em></dt>
<dt><a name="index-gpu_002dapply_002a"></a>Syntax: <strong>gpu-apply*</strong> <em>shader vertex-array count [#:uniform-key uniform-value …]</em></dt>
<dd>
<p>Render <var>vertex-array</var> using <var>shader</var> with the uniform values
specified in the following keyword arguments.
</p>
<p>While <code>gpu-apply</code> will draw every vertex in <var>vertex-array</var>,
<code>gpu-apply*</code> will only draw <var>count</var> vertices.
</p></dd></dl>
<dl>
<dt><a name="index-gpu_002dapply_002finstanced"></a>Syntax: <strong>gpu-apply/instanced</strong> <em>shader vertex-array n [#:uniform-key uniform-value …]</em></dt>
<dt><a name="index-gpu_002dapply_002finstanced-1"></a>Syntax: <strong>gpu-apply/instanced</strong> <em>shader vertex-array count n [#:uniform-key uniform-value …]</em></dt>
<dd>
<p>Render <var>vertex-array</var> <var>n</var> times using <var>shader</var> with the
uniform values specified in the following keyword arguments.
</p>
<p>Instanced rendering is very beneficial for rendering the same object
many times with only small differences for each one. For example, the
particle effects described in <a href="Particles.html#Particles">Particles</a> use instanced rendering.
</p>
<p>While <code>gpu-apply/instanced</code> will draw every vertex in
<var>vertex-array</var>, <code>gpu-apply*</code> will only draw <var>count</var>
vertices.
</p></dd></dl>
<dl>
<dt><a name="index-current_002dviewport"></a>Procedure: <strong>current-viewport</strong></dt>
<dd><p>Return the currently bound viewport (see <a href="Viewports.html#Viewports">Viewports</a>).
</p></dd></dl>
<dl>
<dt><a name="index-current_002dframebuffer"></a>Procedure: <strong>current-framebuffer</strong></dt>
<dd><p>Return the currently bound framebuffer (see <a href="Framebuffers.html#Framebuffers">Framebuffers</a>).
</p></dd></dl>
<dl>
<dt><a name="index-current_002dblend_002dmode"></a>Procedure: <strong>current-blend-mode</strong></dt>
<dd><p>Return the currently bound blend mode (see <a href="Blending.html#Blending">Blending</a>).
</p></dd></dl>
<dl>
<dt><a name="index-current_002ddepth_002dtest"></a>Procedure: <strong>current-depth-test</strong></dt>
<dd><p>Return <code>#t</code> if depth testing is currently enabled (see <a href="Blending.html#Blending">Blending</a>).
</p></dd></dl>
<dl>
<dt><a name="index-current_002dtexture"></a>Procedure: <strong>current-texture</strong></dt>
<dd><p>Return the currently bound texture (see <a href="Textures.html#Textures">Textures</a>).
</p></dd></dl>
<dl>
<dt><a name="index-current_002dprojection"></a>Procedure: <strong>current-projection</strong></dt>
<dd><p>Return the currently bound projection matrix (see <a href="Matrices.html#Matrices">Matrices</a>).
</p></dd></dl>
<dl>
<dt><a name="index-with_002dviewport"></a>Syntax: <strong>with-viewport</strong> <em>viewport body …</em></dt>
<dd><p>Evaluate <var>body</var> with the current viewport bound to <var>viewport</var> (see <a href="Viewports.html#Viewports">Viewports</a>).
</p></dd></dl>
<dl>
<dt><a name="index-with_002dframebuffer"></a>Syntax: <strong>with-framebuffer</strong> <em>framebuffer body …</em></dt>
<dd><p>Evaluate <var>body</var> with the current framebuffer bound to
<var>framebuffer</var> (see <a href="Framebuffers.html#Framebuffers">Framebuffers</a>).
</p></dd></dl>
<dl>
<dt><a name="index-with_002dblend_002dmode"></a>Syntax: <strong>with-blend-mode</strong> <em>blend-mode body …</em></dt>
<dd><p>Evaluate <var>body</var> with the current blend mode bound to
<var>blend-mode</var> (see <a href="Blending.html#Blending">Blending</a>).
</p></dd></dl>
<dl>
<dt><a name="index-with_002ddepth_002dtest"></a>Syntax: <strong>with-depth-test</strong> <em>depth-test? body …</em></dt>
<dd><p>Evaluate <var>body</var> with the depth-test disabled if <var>depth-test?</var>
is <code>#f</code>, or enabled otherwise (see <a href="Blending.html#Blending">Blending</a>).
</p></dd></dl>
<dl>
<dt><a name="index-with_002dtexture"></a>Syntax: <strong>with-texture</strong> <em>texture body …</em></dt>
<dd><p>Evaluate <var>body</var> with the current texture bound to <var>texture</var>
(see <a href="Textures.html#Textures">Textures</a>).
</p></dd></dl>
<dl>
<dt><a name="index-with_002dprojection"></a>Syntax: <strong>with-projection</strong> <em>projection body …</em></dt>
<dd><p>Evaluate <var>body</var> with the current projection matrix bound to
<var>projection</var> (see <a href="Matrices.html#Matrices">Matrices</a>).
</p></dd></dl>
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