While not as accurate as the raytracer, OpenGL lights are well-suited for providing a quick and approximate preview of what the lighting looks like in the raytracer. Note the distinct differences in how each lights a drawing. OpenGL relies on a geometric vertex-by-vertex basis, whereas the raytracer lights a drawing on a pixel-by-pixel basis. Consequently, the resulting output of the two methods is not identical.
Usage of OpenGL lighting is controlled using the Activate source lights option on the Photo-Realism Settings dialog box. OpenGL lights are used when the following conditions have been met:
-
Photo-Realism module is installed.
-
The Shaded view check box in the Activate source lights option is selected.
-
Lights have been placed in the model.
-
The lights in the model are turned on.
-
There are limitations to using OpenGL lights, as illustrated in the following diagrams. In each diagram, the circles represent spotlights. The red circles are spotlights that are visible, and the black circles are spotlights that are not visible.
-
OpenGL lights a triangle only if light hits a vertex on that triangle - any lighting shining in between vertices will not show up on a triangle.
-
Although OpenGL does shine light through solid objects, unlike the raytracer, it does not know when to stop.
The triangle on the left will light because the spotlight is shining on at least one vertex. The triangle on the right will not light because the spotlight shines between the vertices.
The rectangular plane (shape) is drawn as two large triangles. The spotlight circle (shown in red) on the upper-left corner will be visible in the plane because it is shining on a vertex. The spotlight circle (shown in black) in the middle of the plane will not be visible because it does not hit a vertex.