Allow external plugins to intervene more deeply in the rendering process of Sprite (Mesh2d).

[443eb9]

What problem does this solve or what need does it fill?

I'm now trying to create a 2d lighting plugin, but I encountered a very tricky problem: I want to add something similar to normal mapping on sprite/mesh2d to achieve a PBR-like effect. However, if I want to render another independent texture on a separate material from sprite/mesh2d, I need to copy and paste the entire rendering process again.

What solution would you like?

I'm not entirely clear on the specific solution, but I hope to allow Sprite/mesh2d to enter an additional RenderPhase during the Queue stage, and to allow for custom draw functions as well as custom fragment shaders.

What alternative(s) have you considered?

At least make all structs that are related to the sprite/mesh2d rendering public, so I can grab these processed data directly.

Additional context

None.