e85d191b46
- merge v0.01 --> Añadido fileselector - Añadidas fuentes de Gem y Pure Data - pix2jpg incluído en Gem. Archivos de construcción de Gem modificados. - Añadido fichero ompiling.txt con instrucciones de compilación
107 lines
5.4 KiB
HTML
107 lines
5.4 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="Author" content="Mark Danks">
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<meta name="Author" content="IOhannes m zmölnig">
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<title>Lighting</title>
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</head>
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<body>
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<center>
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<h2>
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<u>Lighting</u></h2></center>
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Lighting is an important factor is how we perceive the quality of an image.
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For example, without lighting and shading, a sphere would just look like
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a circle. GEM provides two types of lights, a local light and world
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light.
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<p>OpenGL uses a vertex lighting model. This means that for every
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vertex in the scene, the influence of the light is calculated. The
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color for the polygon is then modified by the light value of all of the
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vertices. This generally produces a very smooth effect, but you will
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occasionally run into rendering artifacts, especially if you use local
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lights. For example, imagine you have a local light close a large
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square. The corners of the square are far away from the light, so
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none of them will be lit very brightly, even though the light itself is
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very close to the surface of the square.
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<p>It is important to realize that lighting is an expensive operation to
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use. The number of polygons that you will be able to render will
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be much lower if lighting is turned on. As usual, the complexity
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of the scene and the speed of your computer and graphics card will greatly
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affect your frame rate.
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<p>GEM has only a maximum of 8 lights at one time. If you try to
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create more lights than that, you will get an error message.
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<p><a href="#Activate">Activate lighting</a>
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<br><a href="#world_light">[world_light]</a> - A directional light
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<br><a href="#light">[light]</a> - A point light in the world
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<br><a href="#Moving">Moving lights</a>
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<p><img SRC="tribar.gif" height=13 width=561>
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<h3>
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<a NAME="Activate"></a>Activate lighting</h3>
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Lighting is activated by sending a message to <i>[gemwin]</i>. If you
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send "lighting 1", then lighting will be turned on. If you send "lighting
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0", then lighting will be turned off. The lighting state is kept
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even if you destroy the gemwin. This means that if you close a patch
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and open another one, the lighting will still be the same.
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<p>Individual lights can be turned on and off by sending a 1 or 0 to the
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left inlet of the light object itself.
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<p><img SRC="tribar.gif" height=13 width=561>
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<h3>
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<a NAME="world_light"></a>[world_light]</h3>
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A <i>[world_light]</i> is a light which exists infintely far away.
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This reduces the computation needed, so your patch can run faster, but
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it means that all of the light rays are parallel. The <i>[world_light]</i>
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is good for objects like the sun and other lighting affects. This
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means that translating a <i>[world_light]</i> has no effect, although rotation
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does.
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<p>The following patch is 03.lighting/01.world_light.pd.
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<center>
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<p><img SRC="world_light.jpg" BORDER=1 height=152 width=370></center>
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<p>The <i>[world_light]</i> has one extra inlet. The right inlet accepts
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three floats to set the color of the light. A <i>[color]</i> object
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would do nothing. In this case, the light is being set to purple.
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The <i>[world_light]</i> also accepts a debug message. The debug message
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turns on and off a graphical representation of the light in the scene.
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The <i>[world_light]</i> looks like a cone. The cone shows the direction
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that the light is coming from. Remember that the actual position
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of the light does not matter, so geos behind the cone will still be lit.
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It is the direction of the light that matters. This is why you can
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rotate the light.
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<p><img SRC="tribar.gif" height=13 width=561>
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<h3>
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<a NAME="light"></a>[light]</h3>
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A <i>[light]</i> object generates a point light in the world. Because
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the light is local to the scene, there is more math to generate the effect
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of the light on the vertices. However, unlike a <i>[world_light]</i>,
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you can translate the <i>[light]</i> object.
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<p>Below is the patch 03.lighting/02.light.pd.
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<center>
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<p><img SRC="light.jpg" BORDER=1 height=215 width=212></center>
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<p>The <i>[light]</i> object has a right inlet for the color, just light
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the <i>[world_light]</i> object. As this patch shows, the light can
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be moved around the scene with both <i>[rotate]</i> and <i>[translate]</i>
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objects. If you were to set the translate X value equal to 1.0, then
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the sphere would not be lit at all. This is because the light would
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be inside of the sphere. When you turn on the debug representation,
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it is a sphere with its origin where the light it. The <i>[light]</i>
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object does not have any size. It exists as a point source.
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<p><img SRC="tribar.gif" height=13 width=561>
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<h3>
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<a NAME="Moving"></a>Moving lights</h3>
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The patch 03.lighting/03.controlLights.pd allows you to move a <i>[light]</i>
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and <i>[world_light]</i> object in the same scene to see the difference between
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the two objects.
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<p>The patch 03.lighting/04.moveSpheres.pd is an example which moves
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two spheres around the world. Turn on and off the individual lights
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for a demonstration of a local versus infinite light.
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<p>The patch 03.lighting/05.materials.pd uses the material objects to
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selectively control the color of the object. Notice that the diffuse object
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sets the "overall" color, while the specular objects sets the bright reflective
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area where the light directly shines.
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<p><img SRC="tribar.gif" height=13 width=561>
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<p><a href="index.html">[return]</a>
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<br>
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</body>
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</html>
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