In short, DXT1 is for fully opaque textures, and DXT5 is for textures with transparency. As with every compression, a bit of detail is lost during the process. You might see an uncompressed texture every now and then when the creator desired to keep the highest possible image fidelity. And of course since they are uncompressed, they need more memory to be stored. I'm not sure about PO though. Personally I've never felt the need to store a texture without DXT compression.
DXT5 textures can be either semi- or full-transparent. Semi-transparent means every pixel in the texture can be either "on" or "off" regarding transparency - this kind of texture is mostly used in trees and horizon in the original tracks.
Fully transparent textures can have a whole gradient of transparency values, so you can simulate materials like glass - where you can see the object and see through it at the same time.
You should keep all your textures in DXT1 unless you specifically need some part of it to be transparent - your .wad will be smaller, which means shorter loading times. For most textures with transparency, semi-transparent DXT5 is enough. You should keep full DXT5 to translucent objects like glass, and I also recommend full DXT5 for catch fences.
Fences are a particular case not because of the object itself (on paper, a fence perfectly fits the description of either "on" or "off" transparency), but because of the mipmaps. Each texture has four mipmaps which switch in game view depending on how far the object is - when the object is near, the highest resolution mipmap is shown. The problem with semi-transparency is that the on-off behavior also affect the mipmaps, and this effect in fences will lead to a "noisy" effect as you run past them that I personally find very annoying and distracting. Switching the texture to full transparency before generating the lower mipmaps leads to much smoother results.
And when in doubt, check the original .wad files from the unmodded game. Modders can do some crazy stuff
Edit: I forgot to mention that when too many DXT5 transparent textures are on the screen at the same time, the game's graphical engine can get confused and show objects in improper positions, or show through objects that should be solid. I also ran into the same trouble when using both transparent and opaque textures on the same object - in these cases, simply detaching the transparent part into a separate object was enough to fix the issue.
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f1virtualblog@gmail.comEdited 2 time(s). Last edit at 10/03/2019 03:16PM by Prblanco.