fix(textureloader): Simplify and fix faulty implementations of texture reduction (2)

[xezon]

• Follow up for bugfix(textureloader): Fix faulty texture reduction implementations #2789

This change further simplifies and fixes the implementations of texture reduction.

I tested retail vs patched game with different texture reduction levels and it looked identical.

[greptile-apps]

Greptile Summary

This PR follows up on #2789 by further simplifying and fixing the texture reduction pipeline for all three texture types (2D, cube, and volume). The core fix moves the reduced Width/Height/Depth values into the class members in Begin_Compressed_Load, eliminating the duplicate >>= Reduction shift that was incorrectly re-applied inside Load_Compressed_Mipmap. Apply_Mip_Reduction is also refactored to subtract the reduction amount in a single place after both branches, and a WWASSERT is added to guard the unsigned subtraction.

• Double-reduction bug fixed: Load_Compressed_Mipmap for all three texture types previously re-shifted width/height by Reduction even though Get_Width()/Get_Height() were intended to return the already-unreduced originals; the new flow stores the already-reduced dimensions in Width/Height from the beginning, so no second shift is needed.
• MipLevelCount initialization corrected: The task constructor now initialises MipLevelCount to MIP_LEVELS_ALL instead of the raw literal 0, matching the sentinel value the rest of the code checks.
• Named constants and assertion added: Magic literals 4u/1u are replaced by MinTextureDim/MinTextureDepth, and WWASSERT guards are added before unsigned subtractions and surface copies to catch invariant violations early.

Confidence Score: 4/5

Safe to merge with one issue worth addressing: WWASSERT(reduction < mip_level_count) before an unsigned subtraction is the only runtime guard; if that assert compiles out in retail builds and the invariant is violated by a corrupt DDS, the subtraction wraps around and the resulting huge mip count is passed directly to the D3D texture-creation API.

The logic consolidation in Apply_Mip_Reduction — subtracting reduction unconditionally after both branches — is correct, and Validate_Reduction normally guarantees the invariant holds. However, the old code had an explicit mip_level_count < 1 safety floor that was removed without a release-safe equivalent. If a corrupt file produces an unexpected mip_count, the unsigned wrap-around on mip_level_count -= reduction can silently produce a catastrophically large value that gets forwarded to DirectX.

Core/Libraries/Source/WWVegas/WW3D2/textureloader.cpp — specifically the Apply_Mip_Reduction function and the unsigned subtraction at line 1496.

Important Files Changed

Filename	Overview
Core/Libraries/Source/WWVegas/WW3D2/textureloader.cpp	Fixes texture reduction logic across 2D, cube, and volume texture load paths: constructor init, removal of double-reduction in Load_Compressed_Mipmap, consolidation of mip subtraction in Apply_Mip_Reduction, and named constants. Logic is correct; one potential unsigned underflow path if the WWASSERT is compiled out in release.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Begin_Compressed_Load] --> B[Get_Texture_Information]
    B --> C[Validate_Reduction\nensures reduction < mip_count]
    C --> D[Width = orig_width\nHeight = orig_height]
    D --> E[Apply_Dim_Reduction\nstored directly in Width/Height]
    E --> F[Apply_Mip_Reduction\nuses already-reduced Width/Height]
    F --> G{mip_level_count == MIP_LEVELS_ALL?}
    G -- Yes --> H[mip_level_count = mip_count]
    G -- No --> I[mip_level_count = min requested, mip_count]
    H --> J[WWASSERT reduction < mip_level_count]
    I --> J
    J --> K[mip_level_count -= reduction]
    K --> L[clamp to max_mip_level_count]
    L --> M[Create DX8 Texture with reduced Width x Height]
    M --> N[Load_Compressed_Mipmap]
    N --> O[width = Get_Width - already reduced]
    O --> P{level < mip_level_count?}
    P -- Yes --> Q[WWASSERT width >= 4 && height >= 4]
    Q --> R[Copy_Level_To_Surface]
    R --> S[width >>= 1 / height >>= 1]
    S --> P
    P -- No --> T[Done]

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%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
    A[Begin_Compressed_Load] --> B[Get_Texture_Information]
    B --> C[Validate_Reduction\nensures reduction < mip_count]
    C --> D[Width = orig_width\nHeight = orig_height]
    D --> E[Apply_Dim_Reduction\nstored directly in Width/Height]
    E --> F[Apply_Mip_Reduction\nuses already-reduced Width/Height]
    F --> G{mip_level_count == MIP_LEVELS_ALL?}
    G -- Yes --> H[mip_level_count = mip_count]
    G -- No --> I[mip_level_count = min requested, mip_count]
    H --> J[WWASSERT reduction < mip_level_count]
    I --> J
    J --> K[mip_level_count -= reduction]
    K --> L[clamp to max_mip_level_count]
    L --> M[Create DX8 Texture with reduced Width x Height]
    M --> N[Load_Compressed_Mipmap]
    N --> O[width = Get_Width - already reduced]
    O --> P{level < mip_level_count?}
    P -- Yes --> Q[WWASSERT width >= 4 && height >= 4]
    Q --> R[Copy_Level_To_Surface]
    R --> S[width >>= 1 / height >>= 1]
    S --> P
    P -- No --> T[Done]

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
Core/Libraries/Source/WWVegas/WW3D2/textureloader.cpp:1495-1496
**Unsigned underflow if assert is disabled in release**

`WWASSERT` is typically stripped in release/retail builds. If, despite `Validate_Reduction`'s guards, `reduction >= mip_level_count` ever occurs (e.g., due to a corrupt DDS file returning a smaller-than-expected `mip_count`), the unsigned subtraction on the next line silently wraps around to `~0u`. That value is then passed as `MipLevelCount` to `DX8Wrapper::_Create_DX8_Texture`, almost certainly producing a crash or D3D error rather than a graceful fallback. The old code had an explicit `if (mip_level_count < 1) mip_level_count = 1;` safety net; the new consolidation removed it without an equivalent release-safe guard.

_{Reviews (2): Last reviewed commit: "Simplify Apply_Mip_Reduction" | Re-trigger Greptile}

[Skyaero42]

Looks good