[BUG]: Gran Turismo 4 — 3D Texture Replacements Incorrectly Matched or Applied

Describe the Bug

Describe the Bug

Gran Turismo 4 has an issue with the HD Texture Replacement system where a large portion of 3D replacement textures are incorrectly matched or applied.

HD replacement textures for the HUD and interface are loaded and displayed correctly. However, most vehicle and environment replacement textures do not appear as their corresponding HD textures.

Instead, many of these textures continue to look like the original game textures, while enabling Texture Replacements still changes their appearance. Some textures become noticeably more saturated, and certain vehicle textures develop small dot-like artifacts and visible breakup of color gradients.

In some cases, the resulting image appears as if a replacement texture is being applied to a different texture resource than the one it was intended for, such as an environment or reflection texture.

When Texture Replacements are disabled, the game renders normally using the original textures. The incorrect visual changes only occur when Texture Replacements are enabled.

The fact that HUD/UI replacements work correctly while a large portion of 3D replacements produce incorrect results suggests that this is not a general failure to load replacement textures, but an issue affecting the matching or application of certain 3D texture resources.

The issue occurs with both Vulkan and OpenGL and has been reproduced across multiple PCSX2 versions.

Reproduction Steps

Reproduction Steps

1. Launch Gran Turismo 4 NTSC-U (SCUS-97328) in PCSX2.
2. Enable Texture Replacements.
3. Use the Gran Turismo 4 Retexture Mod v3.0.4.
4. Enter a race or any area where vehicle and environment 3D textures are displayed.
5. Observe the replaced textures.
6. Compare the result with Texture Replacements disabled.

With Texture Replacements enabled, HUD/UI replacement textures are displayed correctly, while many vehicle and environment 3D textures are not replaced with their corresponding HD textures and instead show the described visual artifacts/color changes.

Expected Behavior

Expected Behavior

Each HD replacement texture should be correctly matched to its corresponding original game texture and applied to the intended 3D texture resource.

Vehicle and environment textures should display the corresponding HD replacement textures without incorrect texture matching, color changes, or visual artifacts.

HUD/UI replacement textures should continue to work as they currently do.

PCSX2 Revision

2.9.54

Operating System

Windows 11

If Linux - Specify Distro

No response

Logs & Dumps

No response