Apply vertex shader

[huand]

Hello!
I would like to apply deformation to a mesh.
Let's take the Triangle example. If I wanted to modify individually the vertex positions (so not a global set_transformation) without re-sending from a CPU mesh, how would i go about it?
I've seen the egui example using a vertex shader. Would this approach work also in three-d?
Thanks

[huand]

looking through the doc, i guess i need to use the core::Program struct?

[asny]

That's a good question, I have several suggestions:

• You can change the positions in the vertex shader (as I think you are suggesting) which is only limited by the fact that you need to be able to compute the position in a vertex shader. For that, you can create a new Geometry type, for inspiration, you can take a look at the water implementation in water.rs and water.vert which uses exactly this approach to deform the waves. If you only want to use the core module, then, yes, you need to create a Program which deforms the vertex positions in the vertex shader.
• You might be able to do it with morph targets (Morph targets #308), where the data is transferred once to the GPU, but it requires that there's a limit to how it can deform. Also that's not implemented yet 😕
• You can update the position VertexBuffer data when it changes using VertexBuffer::fill. This solution is less performant than morph targets, but it is also more flexible. To actually use this, you have to implement something like the Mesh so you have access to your vertex buffers and can update them. The simple solution would just be to copy the Mesh struct and what else you need 🙂
• The last solution would be to recreate the static mesh each time it changes, so resend all the data to the GPU.

[huand]

thanks for the detailed answer!
I will have a look in all solutions you proposed.

For info:
My goal is to make a visualization for rail curves. Typically railway curve use a smooth/linearly varying curvature. So using egui to set the curvature along the rail, integrate the curve (center of the rail curve), then define the physical rail mesh from this center curve (left/right) and visualize it with three-d. I would define the rail mesh by taking orthogonal slices on the path and mesh between 2 adjacent slices. I was thinking maybe I can just send the transform for each "slices" of the mesh to update the 3d positions.

Hopefully I can post it soon in the show & tell section ! 🤞

[asny]

thanks for the detailed answer!

No problem 🙂

I'm not sure I got everything, but sure sounds like an interesting problem 🤓 If some part of the rail mesh stays static (the mesh between two slices), then I think it's a good idea to create that as a Mesh and then repeatedly update it's transformation, then draw it, then update it's transformation and draw it again. The more optimal way would be to use an InstancedMesh and then draw everything at once. I'm not sure that's a possible solution though 🙂

Hopefully I can post it soon in the show & tell section ! 🤞

Sounds great 👍