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-<span id="Shaders"></span><div class="header">
-<p>
-Next: <a href="Framebuffers.html" accesskey="n" rel="next">Framebuffers</a>, Previous: <a href="Buffers.html" accesskey="p" rel="prev">Buffers</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> &nbsp; [<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>
-</div>
-<hr />
-<span id="Shaders-1"></span><h4 class="subsection">5.3.13 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 graphics 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 &ldquo;attributes&rdquo; (positional
-arguments), and some &ldquo;uniforms&rdquo; (keyword arguments).
-</p>
-<div class="lisp">
-<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">my-shader</span> <span class="syntax-open">(</span><span class="syntax-symbol">load-shader</span> <span class="syntax-string">"vert.glsl"</span> <span class="syntax-string">"frag.glsl"</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
-<span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">vertices</span> <span class="syntax-open">(</span><span class="syntax-symbol">make-vertex-array</span> <span class="syntax-symbol">...</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
-<span class="syntax-open">(</span><span class="syntax-symbol">shader-apply</span> <span class="syntax-symbol">my-shader</span> <span class="syntax-symbol">vertices</span> <span class="syntax-keyword">#:color</span> <span class="syntax-symbol">red</span><span class="syntax-close">)</span>
-</pre></div>
-
-<p>See <a href="Rendering-Engine.html">Rendering Engine</a> for more details about the <code>shader-apply</code>
-procedure.
-</p>
-<p>Shaders are incredibly powerful tools, and there&rsquo;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 id="index-strings_002d_003eshader">Procedure: <strong>strings-&gt;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 id="index-load_002dshader">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 id="index-make_002dshader">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 id="index-shader_003f">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 id="index-null_002dshader">Variable: <strong>null-shader</strong></dt>
-<dd><p>Represents the absence shader program.
-</p></dd></dl>
-
-<dl>
-<dt id="index-shader_002duniform">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 id="index-shader_002duniforms">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 id="index-shader_002dattributes">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 id="index-shader_002duniform_002dset_0021">Procedure: <strong>shader-uniform-set!</strong> <em>shader uniform value</em></dt>
-</dl>
-
-<span id="Attributes"></span><h4 class="subsubsection">5.3.13.1 Attributes</h4>
-
-<dl>
-<dt id="index-attribute_003f">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 id="index-attribute_002dname">Procedure: <strong>attribute-name</strong> <em>attribute</em></dt>
-<dd><p>Return the variable name of <var>attribute</var>.
-</p></dd></dl>
-
-<dl>
-<dt id="index-attribute_002dlocation">Procedure: <strong>attribute-location</strong> <em>attribute</em></dt>
-<dd><p>Return the binding location of <var>attribute</var>.
-</p></dd></dl>
-
-<dl>
-<dt id="index-attribute_002dtype">Procedure: <strong>attribute-type</strong> <em>attribute</em></dt>
-<dd><p>Return the data type of <var>attribute</var>.
-</p></dd></dl>
-
-<span id="Uniforms"></span><h4 class="subsubsection">5.3.13.2 Uniforms</h4>
-
-<dl>
-<dt id="index-uniform_003f">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 id="index-uniform_002dname">Procedure: <strong>uniform-name</strong> <em>uniform</em></dt>
-<dd><p>Return the variable name of <var>uniform</var>.
-</p></dd></dl>
-
-<dl>
-<dt id="index-uniform_002dtype">Procedure: <strong>uniform-type</strong> <em>uniform</em></dt>
-<dd><p>Return the data type of <var>uniform</var>.
-</p></dd></dl>
-
-<dl>
-<dt id="index-uniform_002dvalue">Procedure: <strong>uniform-value</strong> <em>uniform</em></dt>
-<dd><p>Return the current value of <var>uniform</var>.
-</p></dd></dl>
-
-<span id="User_002dDefined-Shader-Types"></span><h4 class="subsubsection">5.3.13.3 User-Defined Shader Types</h4>
-
-<p>The shader examples in this manual thus far have only shown uniforms
-defined using primitive types. However, GLSL shaders support
-user-defined compound structs, such as this one:
-</p>
-<div class="example">
-<pre class="verbatim">struct Light {
- bool enabled;
- int type;
- vec3 position;
- vec3 direction;
- vec4 color;
- float intensity;
- float cutOff;
-};
-
-uniform Light light;
-</pre></div>
-
-<p>While <code>light</code> is declared as a single uniform in the shader code,
-OpenGL translates this into <em>seven</em> uniforms in this case: One
-uniform each member of the <code>Light</code> struct. This poses a problem
-for sending Scheme data to the GPU. How can compound Scheme data
-translate into compound uniform data on the GPU? The answer is with
-shader types. Shader types are a special kind of Guile struct that
-provide a one-to-one mapping between a Scheme data structure and a
-shader struct.
-</p>
-<p>Some example code will explain this concept best. Here is the Scheme
-equivalent of the <code>Light</code> struct:
-</p>
-<div class="lisp">
-<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-special">define-shader-type</span> <span class="syntax-symbol">&lt;light&gt;</span>
- <span class="syntax-symbol">make-light</span>
- <span class="syntax-symbol">light?</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">bool</span> <span class="syntax-symbol">enabled</span> <span class="syntax-symbol">light-enabled?</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">int</span> <span class="syntax-symbol">type</span> <span class="syntax-symbol">light-type</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">float-vec3</span> <span class="syntax-symbol">position</span> <span class="syntax-symbol">light-position</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">float-vec3</span> <span class="syntax-symbol">direction</span> <span class="syntax-symbol">light-direction</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">float-vec4</span> <span class="syntax-symbol">color</span> <span class="syntax-symbol">light-color</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">float</span> <span class="syntax-symbol">intensity</span> <span class="syntax-symbol">light-intensity</span><span class="syntax-close">)</span>
- <span class="syntax-open">(</span><span class="syntax-symbol">float</span> <span class="syntax-symbol">cut-off</span> <span class="syntax-symbol">light-cut-off</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
-</pre></div>
-
-<p>The macro <code>define-shader-type</code> closely resembles the familiar
-<code>define-record-type</code> from SRFI-9, but with one notable
-difference: Each struct field contains type information. The type
-must be one of several primitive types (documented below) or another
-shader type in the case of a nested structure.
-</p>
-<p>It is important to note that the names of the shader type fields
-<em>must</em> match the names of the struct members in the GLSL code,
-otherwise Chickadee will be unable to perform the proper translation.
-</p>
-<p>As of this writing, this interface is new and experimental. It
-remains to be seen if this model is robust enough for all use-cases.
-</p>
-<p>Primitive data types:
-</p>
-<dl>
-<dt id="index-bool">Variable: <strong>bool</strong></dt>
-<dd><p>Either <code>#t</code> or <code>#f</code>.
-</p></dd></dl>
-
-<dl>
-<dt id="index-int">Variable: <strong>int</strong></dt>
-<dd><p>An integer.
-</p></dd></dl>
-
-<dl>
-<dt id="index-unsigned_002dint">Variable: <strong>unsigned-int</strong></dt>
-<dd><p>An unsigned integer.
-</p></dd></dl>
-
-<dl>
-<dt id="index-float">Variable: <strong>float</strong></dt>
-<dd><p>A floating point number.
-</p></dd></dl>
-
-<dl>
-<dt id="index-float_002dvec2">Variable: <strong>float-vec2</strong></dt>
-<dd><p>A 2D vector (see <a href="Vectors.html">Vectors</a>.)
-</p></dd></dl>
-
-<dl>
-<dt id="index-float_002dvec3">Variable: <strong>float-vec3</strong></dt>
-<dd><p>A 3D vector (see <a href="Vectors.html">Vectors</a>.)
-</p></dd></dl>
-
-<dl>
-<dt id="index-float_002dvec4">Variable: <strong>float-vec4</strong></dt>
-<dd><p>A color (see <a href="Colors.html">Colors</a>) or rectangle (see <a href="Rectangles.html">Rectangles</a>.)
-</p></dd></dl>
-
-<dl>
-<dt id="index-mat3">Variable: <strong>mat3</strong></dt>
-<dd><p>A 3x3 matrix (see <a href="Matrices.html">Matrices</a>.)
-</p></dd></dl>
-
-<dl>
-<dt id="index-mat4">Variable: <strong>mat4</strong></dt>
-<dd><p>A 4x4 matrix (see <a href="Matrices.html">Matrices</a>.)
-</p></dd></dl>
-
-<dl>
-<dt id="index-sampler_002d2d">Variable: <strong>sampler-2d</strong></dt>
-<dd><p>A texture (see <a href="Textures.html">Textures</a>.)
-</p></dd></dl>
-
-<dl>
-<dt id="index-sampler_002dcube">Variable: <strong>sampler-cube</strong></dt>
-<dd><p>A cube map (see <a href="Textures.html">Textures</a>.)
-</p></dd></dl>
-
-<dl>
-<dt id="index-local_002dfield">Variable: <strong>local-field</strong></dt>
-<dd><p>A special type that means that the data is for the client-side
-(Scheme-side) only and should not be sent to the GPU. Any object may
-be stored in a local field.
-</p></dd></dl>
-
-<dl>
-<dt id="index-define_002dshader_002dtype">Syntax: <strong>define-shader-type</strong> <em>&lt;name&gt; constructor predicate (field-type field-name [field-getter] [field-setter]) &hellip;</em></dt>
-<dd>
-<p>Define a new shader data type called <var>&lt;name&gt;</var>.
-</p>
-<p>Instances of this data type are created by calling the
-<var>constructor</var> procedure. This procedure maps each field to a
-keyword argument. A shader data type with the fields <code>foo</code>,
-<code>bar</code>, and <code>baz</code> would have a constructor that accepts the
-keyword arguments <code>#:foo</code>, <code>#:bar</code>, and <code>#:baz</code>.
-</p>
-<p>A procedure named <var>predicate</var> will test if an object is a
-<var>&lt;name&gt;</var> shader data type.
-</p>
-<p>Fields follow the format <code>(field-type field-name [field-getter]
-[field-setter])</code>. <var>field-type</var> and <var>field-name</var> are required
-for each field, but <var>field-getter</var> and <var>field-setter</var> are
-optional.
-</p>
-</dd></dl>
-
-<dl>
-<dt id="index-shader_002ddata_002dtype_003f">Procedure: <strong>shader-data-type?</strong> <em>obj</em></dt>
-<dd><p>Return <code>#t</code> if <var>obj</var> is a shader data type object.
-</p></dd></dl>
-
-<hr />
-<div class="header">
-<p>
-Next: <a href="Framebuffers.html" accesskey="n" rel="next">Framebuffers</a>, Previous: <a href="Buffers.html" accesskey="p" rel="prev">Buffers</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> &nbsp; [<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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