Example for custom Transform

[r0levrai]

Could we have an example of how to write your custom Transform system?

The current Transform exactly packs a 3d translation, rotation and scale ; but there are plenty of cases where you could want more (other affine transformations like shearing (#14622, #4822), projective transformations (#4207), nonlinear stuff, etc), less (2D, no rotations, uniform scaling, etc), or just some custom behaviour (asteroid, portal).

My understanding is that it would either imply writing a PostUpdate system that handle the custom behaviour and output into a GlobalTransform, or a vertex shader to apply a custom mat4x4 plus the camera transform (while loosing on the hierarchical composition), or both for simpler cases if you also want to limit the cpu->gpu data sent.

There are no example for using a custom vertex shader while reusing the standard pixel shader, so that would be great too! Although this question is primarly about a cpu-side example for writing to GlobalTransform.

I also just found in #4822 (reply in thread) @HackerFoo made a fork that did something similar, but I think now that GlobalTransform is an Affine3A, it should be significantly simpler?