Write Rendy backend for Turbine-Scene3D

[aaruel]

This is a follow up to issue #70. My goal for this implementation was to leave as much of the original API the same as possible, which I've achieved for the most part aside from some quirks.

In terms of dependencies, there are more crates introduced in this PR than I wanted (serde_json and spirv-reflect). The reason for that is, Rendy's exposure of SPIR-V reflection is minimal, leading to having to perform the reflection manually. I will probably open an issue on their repo addressing this. (amethyst/rendy#188)

Since Rendy/gfx-hal uses Winit, I used Piston's winit_window package but modified to be updated and work nicely with the WindowSettings builder. I will submit a PR on that repo so the dependency is an actual crate. (PistonDevelopers/winit_window#12)

Quirks:

• Scene manages the window by passing in WindowSettings
• The UBOS_PER_FRAME_SIZE constant determines how many draw calls (like DrawTriangles) there can be between frames. It's 4 for debugging but can be increased to something much larger.
• There's a certain structure the shaders must follow because of SPIR-V. Just keep in mind:
  • Attributes layout locations are exact
  • UBO at set 0 binding 0 contains all the uniforms (which should be matched if needed in both vert and frag stages)
  • Sampler2d is always at set 1 binding 0
  • Inputs and outputs should have explicit locations
• Toggling SRGB and Blending are disabled for now.
• Drawing with multiple shaders is not tested but theoretically working.

Examples can be run at scene3d root as such cargo run --example colored_cube --features vulkan

[bvssvni]

winit_window 0.12.0 is now published.

[aaruel]

Thanks, updated cargo.toml

[aaruel]

serde_json is now removed, I missed that there actually was a Rendy method exposing the compiled SPIR-V data.

[bvssvni]

I've been trying to install Vulkan on Ubuntu to test this PR, but without success so far (got problems with NVidia graphics drivers).

[aaruel]

Possibly related, but a lot of people using Rendy reported having trouble with Vulkan validation layers on multiple SDK versions. I was on 1.1.108.0 and the validation layers crashed completely. I updated to 1.1.114.0 and was able to run it, but also got an error about VK_IMAGE_LAYOUT_UNDEFINED, which is pretty commonly reported on the Discord (however it doesn't affect anything as far as I can tell). If you run the examples with --release it should run without the validation layers and avoid the problems altogether.

[bvssvni]

I got problems installing graphics drivers. Adding --release does not work. However, I can build it just fine.

I think this is a fine starting point.

Merging.

[bvssvni]

Thanks!