Index Making Pictures

Solid rendering

Real surfaces often have a sheen to them. Glossy surfaces show a definite highlight, basically an extended image of the lightsource. Here is an example from Peter Dishman's undergraduate project ray-tracer. Solid models are rendered by modelling light paths. Look in particular at the four smallest spheres. You can see highlights from three different lights. Also notice the effect of mirror-like reflections in the central sphere: you can see the other objects reflected in it. This is much easier to do in a ray-tracer than in a surface renderer. You will also notice shadows from each light source. Finally, this project used distributed ray-tracing to give the depth of field effect: near objects are sharp, distant onces are out of focus.

Here is a minimal rendering, of a sphere using a single Lambert light source at the top left and towards the front of the scene.

Here is how constructive solid geometry (CSG) works. There are two spheres in this scene, one positive (which you can see) and one negative (which removes some of the solid material from the first sphere). To render this correctly, we need to know which negative object (if any) the ray was in when it found a positive object. We then take the colour of the positive object but we calculate the normal of the negative one. Finally we reverse this normal and apply the lighting calculation.