[ FF8 ] Regession with blending type 2 in external textures

[myst6re]

Describe the bug

Since FFNx 1.20.x, blending type 2 (substractive) does not work on external textures.

To Reproduce

Use any existing mods using the Tonberry layer for field and go to the BGU elevator.

Expected behavior

See #693

Additional context

Before 1.20.x, the Tonberry layer was emulated via the TexturePacker (CPU side), the built texture was with alpha=127.
For some reason the GPU driver needs textures to have alpha=127 for blending type 4 to work.

[myst6re]

Two options to fix this bug:

• revert the change made in 1.20.0 and emulate the Tonberry compatibility layer on CPU side. Textures will be slower to load
• find why textures need to have alpha=127, and patch FFNx to remove this prerequisite

[julianxhokaxhiu]

As far as I am aware that value comes from the game engine, as we inherit whatever is being sent to use and we compute it against 255.0 so might be something deep in the game to find out.

However this might be a good starting point to investigate in case:
https://github.com/julianxhokaxhiu/FFNx/blob/master/src/common.cpp#L2206-L2224

I'll see if I find more.

//EDIT: this is the only place in the code where we get a generic set state from the game, all the other calls set explicitly what to set. The function where this is called is governed by the game through the driver interface: https://github.com/julianxhokaxhiu/FFNx/blob/master/src/common.cpp#L2239

//EDIT2: Another thing to try is to patch all 255.0 codepaths to use 127.0 for FF8.

//EDIT3: This is where the alpha test is made on the Shader ( FF8 codepath only, as FF7 doesn't use this feature ): https://github.com/julianxhokaxhiu/FFNx/blob/master/misc/FFNx.frag#L212-L252

[myst6re]

Maybe not related, I found the patch you've made long time ago to enable alpha (not the correct formula) on the elevator: 3315ebe

Edit: I have a lot of GEQUAL with alpharef=112 in the elevator field.

[julianxhokaxhiu]

I think I might start to understand what is going, great finding.

Modulate Alpha actually does this in the shader code ( https://github.com/julianxhokaxhiu/FFNx/blob/master/misc/FFNx.frag#L274-L279 ) which simply multiplies the color by the pixel color value. Disabling it simply picks Alpha as it is, which might explain why I got it working back then as alpha didn't had to be "multiplied" by the vertex color when drawing the door texture, but simply inherited.

Not sure if this intel helps, but might help us on crack this specific issue.

[myst6re]

It seems that enabling modulate alpha fixes our issue with mods and do not change anything without mods. Can you confirm?

[julianxhokaxhiu]

The code changed a lot since then, maybe we fixed it at the source since that commit, so I trust your testing. I'm fine reverting that patch ( or merging your PR if you want to open one ). Let me know and thanks :)