Source: 298b3e8f49b4. Check the source page for feature scope.

Runtime texture replacement

Mods can replace the textures the game draws. This page says what is in the game today and what is still open. To make a texture pack, follow Creating mods; the file format is in the Modding API. The feature is experimental and supported on Windows only.

What the game does

• Replacement by fingerprint. When the renderer uploads a texture, it computes a fingerprint (XXH3-64 of the base level's blocks). If a mod has a .lotex2 file for that fingerprint, the replacement is uploaded instead. The export (--export-assets) writes the fingerprint of every texture to textures/index.csv, so no catalog is needed.
• Which textures. Tiled 2D base levels in the formats G8, A8R8G8B8, DXT1, DXT3 and DXT5, with a shorter side over 16 texels. Render targets, resolved surfaces, movie frames and the controller-prompt atlas are never replaced.
• Sizes and formats. The original size or 2x, 4x or 8x larger, at most 8192 pixels per side, as uncompressed RGBA8 or as block-compressed DDS (BC1, BC3, BC4 or BC7). Shaders keep seeing the original texture size, so a larger replacement samples like the original at a higher resolution.
• Loading. Files are read on a background thread. A texture shows the original until its file has been read, usually a few frames later. LO_MODS_TEXTURE_SYNC=1 reads each file during the upload instead.
• Fallbacks. A file that fails validation, or a texture the game uploads in a form the renderer cannot match safely, keeps the original texture. Failures are logged.

In a test over 86 disc-1 field maps and 19 battles, 98.1% of the eligible uploads matched an exported texture. Almost all of the ones that did not match were on two maps of the Experimental Staff Remains.

Still open

• Video memory. There is no video memory budget yet, so a large pack can use a lot of video memory, especially as RGBA8. Prefer DDS payloads, which are about 4 to 8 times smaller.
• GPUs without BC support. DDS replacements are skipped there and the originals stay (some Mali GPUs). RGBA8 replacements still load but need much more memory.
• Shimmer. Where the game samples only the top level of a texture, a larger replacement can shimmer when it is shown smaller.
• Other resources. Models and movies have their own formats, and language packs add letters to fonts (see Modding); a texture pack does not change them. Fonts of the native menu are limited to their texture pages.