ATi Radeon 4000 Series Anti-Aliasing Investigation

Anti-Aliasing Introduction

In 3D graphics, aliasing occurs because of rasterization, the process of converting a scene from vector primitives (essentially infinite resolution) to screen space (finite resolution). Typical aliasing with 3D scenes includes shimmering, jagged edges, line crawling, wiggling surfaces, and similar.

A higher resolution helps to some degree because there are more pixels to interpolate across, but it’s still quite poor at reducing aliasing compared to current hardware anti-aliasing techniques.

Current 3D hardware AA operates on the basic premise of sampling multiple times for a pixel (as opposed to using a single sample), and blending said samples to form the final pixel. The resulting smoother gradients reduce aliasing.

Multi-Sampling Theory (MSAA)

Multi-sampling first debuted on nVidia’s GeForce 3, and is the most popular hardware AA technique currently used in consumer space. This method takes the concept of super-sampling but decouples the shader and texture samples, thereby saving fillrate.

It operates on the concept of rendering only the geometry at a higher resolution (as opposed to super-sampling which renders everything at a higher resolution), then calculating the final color based on whether multiple depth (Z-buffer) values fall on the edge of a polygon or not.

The disadvantage of this method is that it can’t address texture or shader aliasing (since it only anti-aliases polygon edges), but it’s extremely fast compared to super-sampling, and still shows huge improvements in image quality.

Generally speaking, unless you run a very slow GPU setup, you should try to run at least 2xAA, even if it means dropping the resolution a bit. Even 2xAA can provide a substantial improvement in image quality over no AA.