A Compressed Depth Cache

We propose a depth cache that keeps the depth data in compressed format, when possible. Compared to previous work, this requires a more flexible cache implementation, where a tile may occupy a variable number of cache lines depending on whether it can be compressed or not. The advantage of this is that the effective cache size increases proportionally to the compression ratio. We show that the depth-buffer bandwidth can be reduced, on average, by 17%, compared to a system compressing the data after the cache. Alternatively, and perhaps more interestingly, we show that pre-cache compression in all cases increases the effective cache size by a factor of two or more, compared to a post-cache compressor, at equal or higher performance