[IceNine]

DXT3/5 == DXT1 if you have no alpha channel. Just twice as large. Unless, ofcourse, the hardware is doing something funny. nVidia used to have a nasty bug in early GeForce hardware in their DXT1 path for instance, but that's long gone now.

The best format for colour-only is DXT5-YCoCg, but that requires shaders at runtime, which *may* not be as easy as it sounds. Reason is we have at least 2 textures to render, one or both of which may be DXT5-YCoCg. Obviously I'll be looking into that long-term, but for now we're stuck with DXT1 or uncompressed.

The key step is to develop a reasonable metric for figuring out when to try something other than DXT1. This is easy if it's just alpha or no alpha, but hard if we add in DXT5-YCoCg or uncompressed into the mix.

I have a metric that works well for my images - I'll be adding that to SVN shortly. This needs testing. EDIT: r28782 has the change.

The best way to test it out is to remove all your .dds fanart images, restart XBMC and go one by one through your movies while the .dds generates, making a note of any images that don't look all that good. It'll pay to keep a running list of good/bad/good/good etc. so that you can easily compare with the error values XBMC calculates. Then, grab the log file and dump out all the DDS error lines. Compare which ones are good vs bad with the error values you get. Hopefully we can find a decent cut-off value for trying something other than DXT1.

Cheers,
Jonathan

I'm more than willing to lend my eye to this, since i'm a pretty useless coder. Is XBMC using .dds for posters now as well, or still just fanart? I took a quick look at the new GUILargeTextureManager.cpp file and it's quite a bit different from a few weeks ago, so I can't really tell. I was using the hack posted earlier to make it use posters, but I don't think that would work on the latest SVN. If it is already using DDS for posters then great; if not I think it would help this debugging process quite a bit since I noticed a pretty big speed increase on my ION machine when using DDS for posters.

EDIT: Answered my own question by trying it out. For everyone else's reference, the newest SVN does use DDS format for posters as well as fanart. Hooray!