High quality Stable Cascade Stage C previews via previewer.safetensors

[asagi4]

This enables higher-quality previews for Stable Cascade.

It seems to be reasonably fast, too; during my testing speed drops from about 4.2 it/s to ~4 it/s, and you can actually see what it's generating unlike the pixely mess that the latent2rgb method provides.

I don't really like that the previewer filename is used to detect which method to use, but it fits with what the code is currently doing anyway.

The mini-decoder preview method option should probably be generalized somehow rather than calling it "taesd"

[asagi4]

I suppose I could generalize the mechanism so that the latent format class knows how to load its own previewer. I think that would avoid some of the awkwardness of the code.

[comfyanonymous]

Yeah having an enum or something on the latent format to set the type of the previewer would be good I think.

[asagi4]

I was thinking it could just be a "load_preview_decoder" method on the latent format class. That way other code doesn't need to know or care about the filename or the model class.

I'll cook up something later today.

[comfyanonymous]

yeah that should also be good.

[asagi4]

I did a rather minimal refactor to get started.

Notably, the Impact Pack extension broke when I attempted to rename the TAESDPreviewerImpl class into something more generic.

I also added the optional method argument to get_previewer since custom nodes might want to use it themselves without being forced to obey the command line argument (I think that may be why Impact has its own implementation)

[ltdrdata]

I did a rather minimal refactor to get started.

Notably, the Impact Pack extension broke when I attempted to rename the TAESDPreviewerImpl class into something more generic.

I also added the optional method argument to get_previewer since custom nodes might want to use it themselves without being forced to obey the command line argument (I think that may be why Impact has its own implementation)

You don't need to worry about that. If refactoring is applied, it will be reflected.
All that's needed is a grace period once the merge is decided