Index Making Pictures

Rendering Triangles

In surface rendering, it is necessary to model both sides of a solid object, if both sides are meant to be seen. In computer games, this is done as little as possible, because it increases the number of polygons in view and slows down the rendering.

Here is an example from Tomb Raider: The Last Revelation. In this picture Lara Croft is approaching a large urn.

In the next image she is peering into the neck of the urn. You can see right through the side of the urn to the floor below. The triangles which model the urn shape are all there, as can be verified by looking at the urn from the other side. It is just that they are facing away from this viewpoint and thus have been discarded. If you look at the neck of the urn, you will see that the inside of it and the top half of the urn are fully-modelled, both inside and out. This is because both the inside and outside of that part of the urn are visible from normal viewing angles and therefore both have to be modelled.

You can also see that this circular urn is in fact an octagon in cross-section. This is a particularly crude approximation to a circle but again this is to reduce the polygon count. If you look back to the first picture you will see that this is not especially obvious within the body of the urn (the smooth shading hides the polygon boundaries) but it is easily seen around the boundary.