Pixel and Vertex Shading Performance

To delve further into R300’s pixel shading capability, we ran 3DMark 2001’s shader tests. For this, we are looking at performance in the normal and advanced pixel shader test, as well as EMBM and DOT3 bump-mapping. With bump-mapping operations occurring within the pixel shader, examining EMBM and DOT3 is very revealing.





It is interesting to note that the DOT3 performance is actually lower in overall performance when compared to our other tests. This is interesting to note and is likely due to the more complex lighting in the scene. R300’s high bandwidth levels are noted particularly in the advanced pixel shader test, as this makes heavy use of alpha blending, which is notoriously bandwidth intensive.

By using NVIDIA’s Chameleon Mark test, we can really see how pixel shader complexity impacts overall performance. The Real test has a noted drop in performance over both the Shiny and Glass test. While the difference is not critical, upper resolutions do show this to be at roughly 20 fps. With even greater complexity, we can be assured that the performance gap would be even wider.

Vertex Shader

R300’s vertex shader is important in that it not only provides vertex shading capability, but also static T&L operations. The performance of every vertex shader varies in between applications. With a variety of ways to handle geometry data, each vertex shader is optimized for certain methods. The method used by the application and the quality of the code used can vary the overall performance. With this in mind we have run several different geometry tests to examine overall performance.



From these numbers, it is very clear how geometry performance can vary. We have 3DMark’s performance numbers coming in noticeably higher than that of the OpenGL Geometry Benchmark. Why is this? Of course there are a variety of factors involved, but one primary reason is the method of data handling. This dramatically affects performance. The following are some additional benchmarks to further consider performance: