你先搞清楚PC机是用光盘运行的吗？需要为了光盘容量而妥协实时载入性能吗？需要考虑换盘运行的问题 ...
jeffxl 发表于 2011-10-20 02:42 ![]()
问题是，卡神确实使用了一种非常规的纹理压缩格式，也就是说，GPU无法支持的一种压缩纹理。下面是Anandtech的原话：Something else worth discussing while we’re on the subject is Rage’s texture compression format. S3TC (also called DXTC) is the standard compressed texture format, first introduced in the late 90s. S3TC/DXTC achieves a constant 4:1 or 6:1 compression ratio of textures. John Carmack has stated that all of the uncompressed textures in Rage occupy around 1TB of space, so obviously that’s not something they could ship/stream to customers, as even with a 6:1 compression ratio they’d still be looking at 170GB of textures. In order to get the final texture content down to a manageable 16GB or so, Rage uses the HD Photo/JPEG XR format to store their textures. The JPEG XR content then gets transcoded on-the-fly into DXTC, which is used for texturing the game world.
简而言之，Rage保存在硬盘上的纹理仍然是JPEG XR格式的压缩纹理，而在游戏进行当中实时地由CPU或者GPU将其压缩转码为GPU支持的DXT5格式载入显存。对于CPU转码的路径，JPEG XR格式的纹理被CPU转换为压缩比低很多的DXT5格式，然后载入显存，此过程对内存带宽和PCI-e带宽都有相对较高的要求；对于GPU转码的路径，JPEG XR格式的纹理被载入显存，然后经由CUDA转码成DXT5后保存在显存当中。
id的一篇文献专门提到了在CPU和GPU上将纹理实时压缩为DXT5格式的算法，相信用在了id tech5引擎当中。
下面的问题是，这个实时转码的过程究竟对于IO性能提出了多高要求？这个很难说。不过可以肯定的是，如果硬盘上保存的是压缩比为1:4~1:6的DXT5纹理的话，从磁盘实时读取的数据量会是JPEG XR纹理的数倍之多，只会让情况更糟糕。 |
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