rust-gpu vulkano example

An example project on how to integrate rust-gpu with vulkano. It based on vulkano's image example but the glsl shaders are replaced with rust-gpu shaders.

This example is currently based on vulkano v0.34 and rust-gpu v0.9.

These are the important bits to take a look at:

• root Cargo.toml contains important configuration for the entire workspace. Most notably resolver = "2" for dependency resolution and enabling optimizations for build scripts, so that rust-gpu doesn't take forever to compile shaders.
• example's Cargo.toml contains next to the vulkano dependency also a [build-dependency] block declaring a dependency on the rust-gpu compiler spirv-builder. Additionally, we declare two features, to tell the builder to either use your locally installed spirv-tools, that come with the Vulkan SDK, or to build them itself which may take several minutes. It also contains the use-glsl-shader feature by which one can switch between the original glsl and rust-gpu shaders.
• example contains the CPU code and as mentioned above is based on the image example of vulkano. Commit e2719349 contains all changes done to the file, notably:
  • moved shader! macros to a separate mod shaders, where also the shader! macros for rust-gpu shaders reside.
  • Instead of searching for the entry point called "main", assume there is just one entry point and use that. Rust-gpu names the entry point after the module declaration of your entry point function.
  • added required device feature vulkan_memory_model by rust-gpu
• example's build script invokes rust-gpu to compile the rust shaders to SPIR-V shader binaries (.spv). Feel free to add some codegen here.
• example-shaders's Cargo.toml must contain the crate-type = ["dylib"] declaration, otherwise no artifacts may be produced. It also depends on the spirv-std which version must match that of the spirv-builder.
• the image shader can be found in the source of the example-shader project and is a direct port of the glsl shaders used in vulkano's image example. If you are looking for how specific in-builds are named or used, I'd recommend searching though rust-gpu's compile tests for examples.