Episode 1 racer broken LOD?

[fzurita]

It looks like recent changes broke episode 1 racer. Far away textures look black and turn the normal color as you get closer in some areas. This is visible in the very first level.

The fast shader path doesn't have this problem.

[fzurita]

@gonetz @standard-two-simplex this broke very recently.

[ghost]

@gonetz I debugged the situation a little. Only the textures outside of the track use LOD. The texture has 4 tiles and it uses a standard combiner equation

(tile1 - tile0)*lod_frac + tile0

When tile0==0 the texel is fetched correctly from a normal texture. When tile0>0 or tile1>0 the texel is fetched from the atlas but it seems to return black (probably fails).

Therefore, pixels near the camera render correctly, but pixels far away are black.

I don't understand why the atlas is not working. TextureCache::_loadAccurate() seems to set up _pTexture.max_level=3 correctly and does atlas related operations.

[gonetz]

I'll check it asap.

[gonetz]

It seems that uTex1 sampler points to a wrong texture.

[ghost]

I was looking into it at the moment.

The texture has 4 tiles and it uses a standard combiner equation

I was wrong in this, there is one such texture but it is not the affected one.

The affected one has uMaxTile == 0 but detail is enabled. So the shader generates indices 0 and 1 and the second one is sampled from the atlas. But I believe that textures.cpp does not set up an atlas because max_level==0.

[gonetz]

The affected one has uMaxTile == 0 but detail is enabled. So the shader generates indices 0 and 1 and the second one is sampled from the atlas. But I believe that textures.cpp does not set up an atlas because max_level==0.

Yes, we don't need texture atlas in that case. What is RDRAM address of the affected texture? 0x801E3280 ?

Edit: I checked the code. "textures.cpp does not set up an atlas because max_level==0" - true. This part should be corrected since mipmap code expect texture atlas for the second texture.

[ghost]

This part should be corrected since mipmap code expect texture atlas for the second texture.

Mmm, I realize another thing. The shader has one piece of code where if uMaxTile is 1 the texel is fetched from a normal texture

"  else if (uEnableLod == 0 || uMaxTile == 1) {READ_TEX0_MIPMAP(readtex0, uTex1, tcData1);}\n"

But in the detailed case, uMaxTile == 0 because of the way the uniform is set. Reading from the normal uTex1 texture seems to work.

[gonetz]

" else if (uEnableLod == 0 || uMaxTile == 1) {READ_TEX0_MIPMAP(readtex0, uTex1, tcData1);}\n"

The problem is with tex1, but it has the same condition else if (uEnableLod == 0 || uMaxTile == 1) {READ_TEX0_MIPMAP(readtex1, uTex1, tcData1);}

So, the only thing is to correct uMaxTile uniform?

[gonetz]

Fix:

    void update(bool _force) override
    {
        uMinLod.set(gDP.primColor.m, _force);
-       const CachedTexture * _pTexture = textureCache().current[1];
-       if (_pTexture == nullptr)
-           uMaxTile.set(gSP.texture.level, _force);
-       else
-           uMaxTile.set(_pTexture->max_level > 0 ? gSP.texture.level : std::min(gSP.texture.level, 1u), _force);
+       u32 maxLevel = gDP.otherMode.textureDetail == G_TD_DETAIL ? gSP.texture.level + 1 : gSP.texture.level;
+       uMaxTile.set(maxLevel, _force);
        const int uCalcLOD = (gDP.otherMode.textureLOD == G_TL_LOD) ? 1 : 0;
        uEnableLod.set(uCalcLOD, _force);
        uTextureDetail.set(gDP.otherMode.textureDetail, _force);
    }

[ghost]

So, the only thing is to correct uMaxTile uniform?

gSP.texture.level determines the maximum lod, so passing its value increased by one is not a good idea. We should change the condition in the shader instead. Something like,

bool bUseNoAtlas = uEnableLod == 0 || (uTextureDetail == 2 && uMaxTile == 0) && (uTextureDetail != 2 && uMaxTile == 1);

Or perhaps send a new uniform that contains this boolean.

[gonetz]

It seems that a new uniform is a better solution.

[gonetz]

It seems that a new uniform is a better solution.

Done: https://github.com/gonetz/GLideN64/pull/2618

[gonetz]

Fixed