fabi/Syplheed-Reborn
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

fix(texture): crack X360 DXT1 dword-swap; wire correct decode into viewer

Browse Source 
DXT1 (108/137 textures in Base.xpr — the bulk of picture assets) decoded to
noise. Root cause found by RE: Xbox 360 BCn blocks store the two 32-bit words
of each 64-bit sub-block in the opposite order to the PC/DDS layout — colour
endpoints live in the HIGH dword, indices in the low one. The endian field
(k8in16) only fixes byte order within the 16-bit words; it does not reorder the
dwords, so without this every DXT texture transposed endpoints/indices → noise.

Isolation that led here:
 - de-tile proven correct for bpb=8 (coherent per-block signature map; the
   linear read is scrambled) — same faithful Xenos Tiled2D as the verified
   bpb=4 ARGB path (green Acheron backdrop).
 - inspecting a smooth region, coherent colour endpoints appeared only in
   bytes[4..8], with the high-entropy indices in bytes[0..4].

Fix: swap_bc_block_dwords() swaps the two dwords within each 64-bit unit after
the byte-level endian swap, for every BCn format. Verified in the real Rust CLI:
weapon skins (rou_f001_wep_*) now decode to clean, recognisable images.

Viewer: DXT1 is fixed transparently (from_xpr2 feeds tex.data straight to the
GPU as Bc1). Also corrected the uncompressed path — post-swap k_8_8_8_8 is
[A,R,G,B]; reorder to [R,G,B,A] and upload as Rgba8UnormSrgb (was Bgra8, wrong).

Knob: XPR_NO_BC_DWORD_SWAP disables the swap for A/B validation.

KNOWN REMAINING: 16-byte blocks (BC2/DXT3, BC3/DXT5) and BC4/BC5 (DXT5A/DXN)
still need their alpha+colour half layout worked out — they decode to noise for
now. DXT1 + uncompressed + cubemaps are correct.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
MechaCat02
2026-07-10 22:08:23 +02:00
parent 840db9c549
commit 405233e84f
2 changed files with 75 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
crates/sylpheed-viewer/src/asset_loader.rs
View File

@@ -93,8 +93,28 @@ impl AssetLoader for Xpr2TextureLoader {
pub fn x360_texture_to_bevy_image(tex: X360Texture) -> Result<Image, Xpr2LoadError> {
let format = x360_format_to_wgpu(&tex.format)?;
// Uncompressed k_8_8_8_8: after `from_xpr2`'s k8in32 endian swap the bytes
// are in [A,R,G,B] order (verified against the retail Acheron backdrop).
// wgpu has no ARGB format, so reorder to [R,G,B,A] and upload as Rgba8
// (see `x360_format_to_wgpu`). BCn data is already GPU-ready.
let data = match tex.format {
X360TextureFormat::A8R8G8B8 | X360TextureFormat::X8R8G8B8 => {
let opaque = matches!(tex.format, X360TextureFormat::X8R8G8B8);
let mut out = tex.data;
for px in out.chunks_exact_mut(4) {
let (a, r, g, b) = (px[0], px[1], px[2], px[3]);
px[0] = r;
px[1] = g;
px[2] = b;
px[3] = if opaque { 0xFF } else { a };
}
out
}
_ => tex.data,
};
Ok(Image {
data: tex.data,
data,
texture_descriptor: TextureDescriptor {
label: None,
size: Extent3d {
@@ -132,9 +152,9 @@ fn x360_format_to_wgpu(format: &X360TextureFormat) -> Result<TextureFormat, Xpr2
X360TextureFormat::Dxn => TextureFormat::Bc5RgUnorm,
// DXT5A / BC4 — single-channel (gloss, specular, luminance maps)
X360TextureFormat::Dxt5A => TextureFormat::Bc4RUnorm,
// Uncompressed ARGB — Xbox 360 stores as BGRA in memory
// Uncompressed — reordered to [R,G,B,A] by `x360_texture_to_bevy_image`.
X360TextureFormat::A8R8G8B8 | X360TextureFormat::X8R8G8B8 => {
TextureFormat::Bgra8UnormSrgb
TextureFormat::Rgba8UnormSrgb
}
})
}