[aspctt]

TexParameter keeps one set of filter and wrap values for both stages, and the loop that should flag every stage for a refresh only flags stage 0 (textureUnits[0] instead of textureUnits[i]). The refresh also calls glTexParameteri without making that stage's unit active, so stage 0's values can land on whatever stage 1 has bound.

Fixing the index alone would make every value reach both stages, so stage 1's clamps would land on stage 0's textures. In scvk, my Vulkan driver, that model gave black patches on the terrain.

What the DirectX driver does, from SimCity 4 version 641:

• TexParameter (0x884990) writes the value into the active stage's record (0x80 bytes per stage, filter and wrap at +0xc to +0x18). SetTexture (0x884810) never touches those fields, so filter and wrap belong to the stage, not to the texture.
• The game keeps its own cache of wrap (0x7d41e0) and filter (0x7d4280) per stage, and skips TexStage and TexParameter when the stage already holds the value. It relies on each stage keeping its own values.

Changes:

• Each texture unit keeps its own filter and wrap, and TexParameter sets the selected unit's.
• A unit applies its values to the texture it has bound, after a bind or a change, with its own unit active.
• After a draw applies the units, the active unit goes back to the one the game selected with TexStage. A draw could leave another unit active before, and TexEnv, TexStageMatrix and the texture uploads in CreateTexture and LoadTextureLevel all act on the active unit.

In scvk this model fixed building shadows repeating along streets (the shadow mask on stage 1 needs clamp) and black slabs on the cut-away terrain beside sloped lots.

OpenGL still keeps the values on the texture object, so one texture bound to both stages with different values at the same time gets the last stage's.

Tested in game on version 641 with an NVIDIA RTX 3070, against upstream main: building shadows along streets and cloud shadows look right.

[nsgomez]

Thanks, cheers