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<span id="Lights"></span><div class="header">
<p>
Next: <a href="Skyboxes.html" accesskey="n" rel="next">Skyboxes</a>, Previous: <a href="Models.html" accesskey="p" rel="prev">Models</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="Lights-1"></span><h4 class="subsection">5.3.9 Lights</h4>
<p>The <code>(chickadee graphics light)</code> module provides a data type for
dynamic lights that can be used to light 3D objects (such as
<a href="Models.html">Models</a> or <a href="Meshes.html">Meshes</a>.)
</p>
<p>There are 3 types of dynamic lights:
</p>
<ul>
<li> point light:
Emits light in all directions from a specific point in space, like a
light bulb.
</li><li> directional light:
Emits light of a constant intensity in a direction, like sunlight.
</li><li> spot light:
Emits a cone of light in a direction, like a flashlight.
</li></ul>
<dl>
<dt id="index-make_002dpoint_002dlight">Procedure: <strong>make-point-light</strong> <em>[#:position (vec3 0 0 0)] [#:color black] [#:intensity 1]</em></dt>
<dd>
<p>Return a new point light located at <var>position</var> that emits
<var>color</var> light.
</p></dd></dl>
<dl>
<dt id="index-make_002ddirectional_002dlight">Procedure: <strong>make-directional-light</strong> <em>[#:direction (vec3 0 -1 0)] [#:color black] [#:intensity 1]</em></dt>
<dd>
<p>Return a new directional light that emits <var>color</var> light in
<var>direction</var>.
</p></dd></dl>
<dl>
<dt id="index-make_002dspot_002dlight">Procedure: <strong>make-spot-light</strong> <em>[#:position (vec3 0 0 0)] [#:direction (vec3 0 -1 0)] [#:color black] [#:cut-off <em>π/4</em>] [#:intensity 1]</em></dt>
<dd>
<p>Return a new spot light located at <var>position</var> that emits
<var>color</var> light in <var>direction</var> in a cone that cuts off at
<var>cut-off</var> radians.
</p></dd></dl>
<dl>
<dt id="index-point_002dlight_003f">Procedure: <strong>point-light?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a point light.
</p></dd></dl>
<dl>
<dt id="index-directional_002dlight_003f">Procedure: <strong>directional-light?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a directional light.
</p></dd></dl>
<dl>
<dt id="index-spot_002dlight_003f">Procedure: <strong>spot-light?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a spot light.
</p></dd></dl>
<dl>
<dt id="index-light_002dtype">Procedure: <strong>light-type</strong> <em>light</em></dt>
<dd><p>Return the type of <var>light</var>, one of:
</p>
<ul>
<li> point
</li><li> directional
</li><li> spot
</li></ul>
</dd></dl>
<dl>
<dt id="index-light_002dcolor">Procedure: <strong>light-color</strong> <em>light</em></dt>
<dd><p>Return the color of <var>light</var>.
</p></dd></dl>
<dl>
<dt id="index-light_002dintensity">Procedure: <strong>light-intensity</strong> <em>light</em></dt>
<dd><p>Return the intensity of <var>light</var>.
</p></dd></dl>
<dl>
<dt id="index-light_002dposition">Procedure: <strong>light-position</strong> <em>light</em></dt>
<dd><p>Return the position of <var>light</var>. The value is irrelevant for
directional lights.
</p></dd></dl>
<dl>
<dt id="index-light_002ddirection">Procedure: <strong>light-direction</strong> <em>light</em></dt>
<dd><p>Return the direction of <var>light</var>. The value is irrelevant for
point lights.
</p></dd></dl>
<dl>
<dt id="index-light_002dcut_002doff">Procedure: <strong>light-cut-off</strong> <em>light</em></dt>
<dd><p>Return the cosine of the cut off angle of <var>light</var>. The value is
only relevant for spot lights.
</p></dd></dl>
<dl>
<dt id="index-set_002dlight_002dcolor_0021">Procedure: <strong>set-light-color!</strong> <em>light color</em></dt>
<dd><p>Set the color of <var>light</var> to <var>color</var>.
</p></dd></dl>
<dl>
<dt id="index-set_002dlight_002dposition_0021">Procedure: <strong>set-light-position!</strong> <em>light position</em></dt>
<dd><p>Set the position of <var>light</var> to <var>position</var>.
</p></dd></dl>
<dl>
<dt id="index-set_002dlight_002ddirection_0021">Procedure: <strong>set-light-direction!</strong> <em>light direction</em></dt>
<dd><p>Set the direction of <var>light</var> to <var>direction</var>.
</p></dd></dl>
<dl>
<dt id="index-set_002dlight_002dcut_002doff_0021">Procedure: <strong>set-light-cut-off!</strong> <em>light cut-off</em></dt>
<dd><p>Set the cut off angle of <var>light</var> to <var>cut-off</var>.
</p></dd></dl>
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