Opaque solid objects reflect light.
Solid objects can cast shadows.
In these two lectures we will deal with cases 1 to 3. As we shall soon see that the property of convexity significantly simplifies the rendering of opaque objects. A line connecting any two points on the surface of the object is entirely within the object. The centre of gravity of a solid convex object is always inside the object. Hidden Lines for a Single Convex Object Edges are either totally visible or totally hidden.