Draw on Object's faces

Can someone give me a hint of how to project the 2d position onto the face of a 3d object?

I know how to make a drawing effect in spark using screen pan and delay frame, it’s basically just the default screen uv. but I have a problem to project this screen pan to the 3d Object’s face.

I’ve seen Yegor and Denis do this in their effect. But I still have no idea how the projection works.
Any idea?

Here’s how I convert the 3D object coordinates into screen space. If you use this UV on the material, it will act like a passthrough shader for a texture. Is that helpful?

I have seen those guys do some cool stuff that enables drawing directly on 3D objects and I’m not sure how that’s done, but hopefully this is a good starting point if that is your goal.

Yea that’s how the texture UV projection does. but the problem is that the texture doesn’t stick to the object surface, only stick on the 2d screen. it can be seen when we or the object moves. because the mask is captured in the screen uv, not the object’s uv. Projection stuffs really give a headache :dizzy_face: