Digital Foundry: How is HDR being handled this time? The dual framebuffer seemed to get a lot of flak in Halo 3 in terms of the resolution downgrade, but there wasn't much explained about it. Were other framebuffer formats (7e3/FP10 or INT16) just nowhere near comparable? Your previous GDC presentation only described the differences in terms of numbers, but the real-world comparison is difficult to visualise otherwise. What's the approach in Reach?
Chris Tchou: We use a single 7e3 buffer for our final render target in Reach. This results in a more limited HDR (about 8x over the white point, as opposed to 128x in Halo 3) but is much faster for transparents and post-processing. In practice, the difference between 8x and 128x HDR is slight - the main thing you may notice is that the bloom around bright areas loses its color more often, desaturating to white.
And yes, a single 7e3 buffer gives us more available EDRAM for the final lighting pass, but the render resolution is still limited by the three buffers used in the main deferred pass. The resolution in Halo 3 was more limited because we save some EDRAM for dynamic shadows during the lighting pass, alongside the 2 HDR buffers and a depth buffer. But with a single 7e3 buffer, we have plenty of extra room available for the shadows, and it's only limited by the 3 buffers used during the deferred pass.
