LOSTCIRCUITS

Smoothshader 2.0

A significant performance increase in efficacy of vertex shading instructions can be achieved by adding loop, jump and subroutines to the repertoire of capabilities. What it means is that instructions do not have to be repeated, instead, a simple statement of how many times the intruction has to be executed suffices. In trivial terms, a jump means that part of a program can be skipped without modifying the entire program and sub routines are rather self-explanatory.

A great example for SMOOTHSHADER 2.0 is Dynamic Fur Growth using what is probably best described as Hairy Edges (rather than using ATI's terminology). Realistic representation of hair and fur is the most difficult challenge for 3D rendering and it does require a few tricks we would call hairy edges.

Clockwise from upper left: no fur, just fins, fins and shells, just shells. Note how the hairline in the upper right panel follows the polygon edges.

Let's start at the very beginning. Any hair on a flat surface is easy to simulate since it can be done by means of a texture. The problems come in at the edges of polygons where hair would stick out beyond the boundaries of an object, which is why we call them hairy edges. Even within the surface of any object, the triangle borders are where fur motion would be necessary to create realistically looking animations, an illustration is in the upper right panel.

The technique employed by ATI consists of Shells and Fins, that is, superimposed over each surface is a shell that is filled with semi-transparent fins which is enough to create realistic looking hair pieces. Dynamic Fur Growth can be achieved by looping the shell command (for twice as long hair, albeit sparse) or the fin command for higher follicle count or a combination of both.

Next Page:    => Split frame buffers, Beyond Performance, Epitaph =>