Add example showing how to use SpecializedMeshPipeline

[IceSentry]

Objective

• A lot of mid-level rendering apis are hard to figure out because they don't have any examples
• SpecializedMeshPipeline can be really useful in some cases when you want more flexibility than a Material without having to go to low level apis.

Solution

• Add an example showing how to make a custom SpecializedMeshPipeline.

Testing

• Did you test these changes? If so, how?
• Are there any parts that need more testing?
• How can other people (reviewers) test your changes? Is there anything specific they need to know?
• If relevant, what platforms did you test these changes on, and are there any important ones you can't test?

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Showcase

The examples just spawns 3 triangles in a triangle pattern.

[tychedelia]

ty!! so helpful to have more of these mid-level examples

[tychedelia]

nit: could this use world position? even if a bit silly like dividing the color by the position or smth

[IceSentry]

I'd like to keep the shader as simple as possible. I think people using that level of api are able to figure that out. I could maybe rotate the camera a bit to show that it's all already correctly placed in the world.

[IceSentry]

I should probably add a few comments about the world position and instance_index though.

[NotAFile]

This seems very helpful, I did not know this functionality existed! However, based on the comments in the example I'm still slightly confused what the use cases and limitations are and when to use it.

[IceSentry]

I'm still slightly confused what the use cases and limitations are and when to use it

It's a bit hard to explain if, for example, using the material apis was enough for your use case. This api is useful when you want to have more control over how a mesh is rendered than is possible with the material api.

And I guess the limitations are that's it's very verbose? It's also still made with rendering meshes in mind, if you want to make other effects that don't necessarily work with meshes directly then this isn't for you.

[NotAFile]

Ah yep, that seems useful information to add to the example! They're often a bit short on information as to why to do things, I find.

[alice-i-cecile]

This has subtle merge conflicts with #14273 that need to be fixed manually <3