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* Chickadee: (chickadee). Game programming toolkit for Guile.
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<p>
Previous: <a href="Buffers.html#Buffers" accesskey="p" rel="prev">Buffers</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>
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<hr>
<a name="Shaders-1"></a>
<h4 class="subsection">2.3.12 Shaders</h4>
<p>Shaders are programs that the GPU can evaluate that allow the
programmer to completely customized the final output of a GPU draw
call. The <code>(chickadee render shader)</code> module provides an API for
building custom shaders.
</p>
<p>Shaders are written in the OpenGL Shading Language, or GLSL for short.
Chickadee aspires to provide a domain specific language for writing
shaders in Scheme, but we are not there yet.
</p>
<p>Shader programs consist of two components: A vertex shader and a
fragment shader. A vertex shader receives vertex data (position
coordinates, texture coordinates, normals, etc.) and transforms them
as desired, whereas a fragment shader controls the color of each
pixel.
</p>
<p>Sample vertex shader:
</p>
<div class="example">
<pre class="verbatim">#version 130
in vec2 position;
in vec2 tex;
out vec2 fragTex;
uniform mat4 mvp;
void main(void) {
fragTex = tex;
gl_Position = mvp * vec4(position.xy, 0.0, 1.0);
}
</pre></div>
<p>Sample fragment shader:
</p>
<div class="example">
<pre class="verbatim">#version 130
in vec2 fragTex;
uniform sampler2D colorTexture;
void main (void) {
gl_FragColor = texture2D(colorTexture, fragTex);
}
</pre></div>
<p>This manual will not cover GLSL features and syntax as there is lots
of information already available about this topic.
</p>
<p>One way to think about rendering with shaders, and the metaphor
Chickadee uses, is to think about it as a function call: The shader is
a function, and it is applied to some “attributes” (positional
arguments), and some “uniforms” (keyword arguments).
</p>
<div class="example">
<pre class="example">(define my-shader (load-shader "vert.glsl" "frag.glsl"))
(define vertices (make-vertex-array …))
(gpu-apply my-shader vertices #:color red)
</pre></div>
<p>See <a href="Rendering-Engine.html#Rendering-Engine">Rendering Engine</a> for more details about the <code>gpu-apply</code>
procedure.
</p>
<p>Shaders are incredibly powerful tools, and there’s more information
about them than we could ever fit into this manual, so we highly
recommend searching the web for more information and examples. What
we can say, though, is how to use our API:
</p>
<dl>
<dt><a name="index-strings_002d_003eshader"></a>Procedure: <strong>strings->shader</strong> <em>vertex-source fragment-source</em></dt>
<dd><p>Compile <var>vertex-source</var>, the GLSL code for the vertex shader, and
<var>fragment-source</var>, the GLSL code for the fragment shader, into a
GPU shader program.
</p></dd></dl>
<dl>
<dt><a name="index-load_002dshader"></a>Procedure: <strong>load-shader</strong> <em>vertex-source-file fragment-source-file</em></dt>
<dd><p>Compile the GLSL source code within <var>vertex-source-file</var> and
<var>fragment-source-file</var> into a GPU shader program.
</p></dd></dl>
<dl>
<dt><a name="index-make_002dshader"></a>Procedure: <strong>make-shader</strong> <em>vertex-port fragment-port</em></dt>
<dd><p>Read GLSL source from <var>vertex-port</var> and <var>fragment-port</var> and
compile them into a GPU shader program.
</p></dd></dl>
<dl>
<dt><a name="index-shader_003f"></a>Procedure: <strong>shader?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a shader.
</p></dd></dl>
<dl>
<dt><a name="index-null_002dshader"></a>Variable: <strong>null-shader</strong></dt>
<dd><p>Represents the absence shader program.
</p></dd></dl>
<dl>
<dt><a name="index-shader_002duniform"></a>Procedure: <strong>shader-uniform</strong> <em>shader name</em></dt>
<dd><p>Return the metadata for the uniform <var>name</var> in <var>shader</var>.
</p></dd></dl>
<dl>
<dt><a name="index-shader_002duniforms"></a>Procedure: <strong>shader-uniforms</strong> <em>shader</em></dt>
<dd><p>Return a hash table of uniforms for <var>shader</var>.
</p></dd></dl>
<dl>
<dt><a name="index-shader_002dattributes"></a>Procedure: <strong>shader-attributes</strong> <em>shader</em></dt>
<dd><p>Return a hash table of attributes for <var>shader</var>.
</p></dd></dl>
<dl>
<dt><a name="index-uniform_003f"></a>Procedure: <strong>uniform?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a uniform.
</p></dd></dl>
<dl>
<dt><a name="index-uniform_002dname"></a>Procedure: <strong>uniform-name</strong> <em>uniform</em></dt>
<dd><p>Return the variable name of <var>uniform</var>.
</p></dd></dl>
<dl>
<dt><a name="index-uniform_002dtype"></a>Procedure: <strong>uniform-type</strong> <em>uniform</em></dt>
<dd><p>Return the data type of <var>uniform</var>.
</p></dd></dl>
<dl>
<dt><a name="index-uniform_002dvalue"></a>Procedure: <strong>uniform-value</strong> <em>uniform</em></dt>
<dd><p>Return the current value of <var>uniform</var>.
</p></dd></dl>
<dl>
<dt><a name="index-uniform_002ddefault_002dvalue"></a>Procedure: <strong>uniform-default-value</strong> <em>uniform</em></dt>
<dd><p>Return the default value of <var>uniform</var>.
</p></dd></dl>
<dl>
<dt><a name="index-attribute_003f"></a>Procedure: <strong>attribute?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is an attribute.
</p></dd></dl>
<dl>
<dt><a name="index-attribute_002dname"></a>Procedure: <strong>attribute-name</strong> <em>attribute</em></dt>
<dd><p>Return the variable name of <var>attribute</var>.
</p></dd></dl>
<dl>
<dt><a name="index-attribute_002dlocation"></a>Procedure: <strong>attribute-location</strong> <em>attribute</em></dt>
<dd><p>Return the binding location of <var>attribute</var>.
</p></dd></dl>
<dl>
<dt><a name="index-attribute_002dtype"></a>Procedure: <strong>attribute-type</strong> <em>attribute</em></dt>
<dd><p>Return the data type of <var>attribute</var>.
</p></dd></dl>
<hr>
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<p>
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