Lighting

From 2c0b722536a4ec2f723c289b695b983741c678f8 Mon Sep 17 00:00:00 2001 From: Hans-Christoph Steiner Date: Fri, 2 Nov 2012 14:25:59 +0000 Subject: commit windows binaries from old rsync auto-build setup, including Gem 0.93.1 svn path=/trunk/; revision=16520 --- .../noncvs/windows/extra/Gem/manual/Lighting.html | 107 +++++++++++++++++++++ 1 file changed, 107 insertions(+) create mode 100644 packages/noncvs/windows/extra/Gem/manual/Lighting.html (limited to 'packages/noncvs/windows/extra/Gem/manual/Lighting.html') diff --git a/packages/noncvs/windows/extra/Gem/manual/Lighting.html b/packages/noncvs/windows/extra/Gem/manual/Lighting.html new file mode 100644 index 00000000..dcff171c --- /dev/null +++ b/packages/noncvs/windows/extra/Gem/manual/Lighting.html @@ -0,0 +1,107 @@ + + + + + + + Lighting + + + + +

+Lighting

+Lighting is an important factor is how we perceive the quality of an image. +For example, without lighting and shading, a sphere would just look like +a circle. GEM provides two types of lights, a local light and world +light. +

OpenGL uses a vertex lighting model. This means that for every +vertex in the scene, the influence of the light is calculated. The +color for the polygon is then modified by the light value of all of the +vertices. This generally produces a very smooth effect, but you will +occasionally run into rendering artifacts, especially if you use local +lights. For example, imagine you have a local light close a large +square. The corners of the square are far away from the light, so +none of them will be lit very brightly, even though the light itself is +very close to the surface of the square. +

It is important to realize that lighting is an expensive operation to +use. The number of polygons that you will be able to render will +be much lower if lighting is turned on. As usual, the complexity +of the scene and the speed of your computer and graphics card will greatly +affect your frame rate. +

GEM has only a maximum of 8 lights at one time. If you try to +create more lights than that, you will get an error message. +

Activate lighting +
[world_light] - A directional light +
[light] - A point light in the world +
Moving lights +

+Activate lighting

+Lighting is activated by sending a message to [gemwin]. If you +send "lighting 1", then lighting will be turned on. If you send "lighting +0", then lighting will be turned off. The lighting state is kept +even if you destroy the gemwin. This means that if you close a patch +and open another one, the lighting will still be the same. +

Individual lights can be turned on and off by sending a 1 or 0 to the +left inlet of the light object itself. +

+[world_light]

+A [world_light] is a light which exists infintely far away. +This reduces the computation needed, so your patch can run faster, but +it means that all of the light rays are parallel. The [world_light] +is good for objects like the sun and other lighting affects. This +means that translating a [world_light] has no effect, although rotation +does. +

The following patch is 03.lighting/01.world_light.pd. +

+ +

The [world_light] has one extra inlet. The right inlet accepts +three floats to set the color of the light. A [color] object +would do nothing. In this case, the light is being set to purple. +The [world_light] also accepts a debug message. The debug message +turns on and off a graphical representation of the light in the scene. +The [world_light] looks like a cone. The cone shows the direction +that the light is coming from. Remember that the actual position +of the light does not matter, so geos behind the cone will still be lit. +It is the direction of the light that matters. This is why you can +rotate the light. +

+[light]

+A [light] object generates a point light in the world. Because +the light is local to the scene, there is more math to generate the effect +of the light on the vertices. However, unlike a [world_light], +you can translate the [light] object. +

Below is the patch 03.lighting/02.light.pd. +

+ +

The [light] object has a right inlet for the color, just light +the [world_light] object. As this patch shows, the light can +be moved around the scene with both [rotate] and [translate] +objects. If you were to set the translate X value equal to 1.0, then +the sphere would not be lit at all. This is because the light would +be inside of the sphere. When you turn on the debug representation, +it is a sphere with its origin where the light it. The [light] +object does not have any size. It exists as a point source. +

+Moving lights

+The patch 03.lighting/03.controlLights.pd allows you to move a [light] +and [world_light] object in the same scene to see the difference between +the two objects. +

The patch 03.lighting/04.moveSpheres.pd is an example which moves +two spheres around the world. Turn on and off the individual lights +for a demonstration of a local versus infinite light. +

The patch 03.lighting/05.materials.pd uses the material objects to +selectively control the color of the object. Notice that the diffuse object +sets the "overall" color, while the specular objects sets the bright reflective +area where the light directly shines. +

[return] +
+ + -- cgit v1.2.1