On WipeOut HD:
Digital Foundry: Can you give us some firm examples of how you leverage the power of the SPUs in WipEout HD? Can you offload some of the work traditionally done by the GPU onto the SPUs in order to get faster performance?
Studio Liverpool: Definitely, the SPUs are a godsend. We offloaded as much as we could onto the SPUs: physics collision, particle simulation, dynamic lighting, audio, data decompression and particle and trail rendering. We also made good use of the PS3's Edge tools which utilise the SPUs.
As well as relieving the GPU, in WipEout HD the SPUs perform almost all of the CPU's rendering operations such as inserting commands to set render state, set up shaders and issue geometry rendering commands.
Digital Foundry: Can you go into more depth on what advantages the Edge tools give you and how you deployed them in WipEout HD?
Studio Liverpool: We used Edge Geometry for triangle culling to dramatically reduce the vertices we need to process, and because it's a framework it's possible to add our own additional effects during this stage - all of the dynamic lighting effects are computed by the SPUs on the vertices that passed the visibility checks. WipEout HD supports up to 256 of these lights of any size (although it's rare to have more than a few active at once). They have since added Edge Post which provides greater support for SPU implemented framebuffer post processing effects.
Digital Foundry: Can you go into more depth about the lighting, shadowing and post-processing techniques used in WipEout HD? The game looks quite unlike anything else seen on console.
Studio Liverpool: We do as much of the lighting as we can offline. Global illumination and sun occlusion are both computed by an internally developed lighting system and baked onto textures and vertices. The ships themselves have pre-computed ambient occlusion, pre-computed diffuse probes (for image-based lighting) and pre-computed specular probes (for reflections). These are interpolated on the SPUs to light each ship with respect to its location in the scene.
All of our buffers are LDR, but all the lighting computations in the shaders (and dynamic SPU lighting) are HDR. Because our framebuffer is LDR we have a limited range for tone-mapping and bloom, but the artists have a high degree of control (probably a little too high for their liking!) of the entire lighting pipeline.
full interview:
http://www.eurogamer.net/articles/digitalfoundry-wipeout-hd-fury-interview?page=3
