Hi there, my friend asked me to post here some questions about DXT texture formats for which he wants to know answers... :) a) What amount of memory is saved, when using the DXT1-X format... b) and how much memory is saved, if I use an eight-bit palletized textures. Is it really 75% or not? c) What is the speed of the DXT textures loading compared with the other formats? d) When are DXT textures decompressed in the memory? At the moment of rendering or earlier? e) Are there any another interests of using DTX textures? System resources, decompression speed, ... Thank you very much for your answers. EDIT: Please use a more appropriate subject line in future. [Edited by - jollyjeffers on December 13, 2006 9:43:19 AM]

Quote:Original post by Bummer
a) What amount of memory is saved, when using the DXT1-X format...
b) and how much memory is saved, if I use an eight-bit palletized textures. Is it really 75% or not?
c) What is the speed of the DXT textures loading compared with the other formats?
d) When are DXT textures decompressed in the memory? At the moment of rendering or earlier?
e) Are there any another interests of using DTX textures? System resources, decompression speed, ...

a) Compared to what? Compared to a 32 bit texture? DXT1 is 6:1, DXT2-5 is 4:1.

b) Most cards don't support P8 texture anymore. My Geforce3 exposes it on D3D8, but not on D3D9. It would have been 75% though, yeah. Since you can't rely on it being there, it's not really worth supporting. Plus, you have 1 palette to use across all stages.

c) They'll load faster, if used correctly. They're smaller, so they'll load faster. PNGs are compressed on disk, but need to be uncompressed at load, and sent to the card as uncompressed. DXT textures are less to load and less to transfer to the card. DDS files can contain mipmaps. You want to include mips. If you don't, D3DX will uncompress the DXT, generate mips, and compress each level, which will be slow.

d) DXTs are stored on the card compressed. They're decompressed in small chunks as needed during rasterization.

e) DXT1 stores colors as 16 bit, so you might see a bit of quality loss, depending on the texture. Older nVidia hardware interpolates it as 16 bit too, instead of as 32 bit after decompression.

a)Dxt1 compresses to 4bit/pixel, compared to 32bit/pixel it's 1:8, Dxt3 and 5 compress to 8bit/pixel (basically the same colorcompression as dxt, but additional 4bit/pixel for alpha) so it's 1:4

b)dont use it, it's obsolete

c)about 4 or 8times faster if u load already compressed textures

d)usually on loading to the texture-caches

e)u can use the same amount of memory but make the resolution twice as it is with 32bit textures or keep them as they are, but use a lot more textures, kinda nice thing :)

Ok. DXT has been loaded faster to RAM than others (png, jpg..)...How fast can display graphic card DXTs ? is it faster or slower than classical formats (png, jpg...) ?

Quote: In that sense DXT will probably be slower
Jack

Can you tell me..how much is DXT slower than classical formats? (just about in percentage), thanx.