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• Similar request had not already been reported before in the issue tracker.

What has to be improved/added?

Currently, Chunks Fade In attempts to inject its own behavior into shaders. For some shaders, this works just fine. However, the way it does so is not conducive to shaders implementing their own blending behavior (which is necessary for deferred shaders).

My proposal for a shader API is as follows:

In All Programs

• CHUNKS_FADE_IN_ENABLED should be defined whenever CFI is enabled
• CFI_FADE and CFI_ANIMATION macros
  • Named macros should be made available for comparisons (ex: #if CFI_ANIMATION == CFI_ANIMATION_FULL)
  • Disabling fading or animation may be either a separate macro (ex: CFI_FADE_DISABLED), or simply leaving ex: CFI_FADE undefined.

In Gbuffer (and shadow?) Vertex Shaders

• vec3 cfi_VertexDisplacement Vertex displacement from CFI. Should be in a world-aligned coordinate space.
  • This should not include world curvature, as many shaders implement this independently.
• float cfi_FadeFactor A 0-1 number representing the animation timeline for this chunk
• float cfi_RefFactor
  • For Fade Lined, this represents when in the animation the vertex should be shown (linear interpolation should work fine for this)
  • For Fade Block, this is a per-block random number
  • For Fade Vertex, this is a per-vertex random number

The above variables should contain everything a shader developer needs in order to replicate the current behavior, or pretty much anything else that uses the linear fade factor.
Once Distant Horizons support is implemented, ideally the same information should be available in Distant Horizons passes. However, some likely concessions may have to be made. Namely, vertex displacement / noisy vertex attributes may not work as anticipated on DH terrain due to greedy meshing.

Helper methods

The following functions are (optionally) provided to provide completely identical functionality to the current behavior:
float cfi_CalculateFade(float cfi_FadeFactor, float cfi_RefFactor)
vec3 cfi_Displace(vec3 eyePlayerPos, vec3 cfi_VertexDisplacement)

Handling Shaders that Don't Implement Support

There are two main methods of approach here.

The first is similar to the current behavior, but would check for a macro or variable reference first (ex: if CHUNKS_FADE_IN_SUPPORTED appears anywhere in any program, or if a variable injected by CFI is used somewhere). This has the advantage of making some shaders work from CFI's end, but would also produce very broken results on others.

Supporting additional shaders would require creating dedicated patchers for them, similar to how Iris supported specific popular shaders even before becoming feature complete.

The other option is to simply leave it to shaders to support the mod (when shaders are enabled). This would result in far fewer shaders working with this mod, but it wouldn't break any shaders either.