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An implementation of multiresolution (Nanite/Meshlet) style rendering in Rust and Vulkan.

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[Read the dissertation on this project!](https://pettett.github.io/projects/meshes/main.pdf)

# Multires

This repository is a proof of concept implementation of a multiresolution mesh rendering system following designs originally developed in _Batched Multi-Triangulation_ and _Nanite_.

It contains:

- Two simplification backends:
   	- Quadric error metrics (custom implementation, non uniform tessellation)
   	- `meshopt` (no support for simplifying boundaries)
- Two procedural geometry backends:
   	- Primitive shading (proof of concept, slow)
   	- Mesh Shading (blazing fast)
- Two cluster selection algorithms:
   	- DAG traverse - explore the DAG from the roots down, finding clusters that fit the error threshold.
   	- Adaptive Select - dispatch an invocation for each cluster that may be drawn (based on last frame). With mesh shading, this dispatches task shaders, with no intermediate memory usage.

## Baking Meshes

First, obtain a `.glb` mesh. For best results, ensure no microholes/small gaps and smooth geometry.
My demo mesh is a cleaned up version of the stanford dragon, available [here](https://github.com/pettett/dragon_high).

Bake the mesh with default settings:

```
mkdir assets
cargo run -r --bin=baker -- --input=MODELS_DIR/dragon_high.glb --output=assets/
```

A large amount of text detailing each pass of simplification is expected.

The result will be a file `assets/dragon_high.glb.bin`, a binary encoding of the mesh. No effort has been put into optimising the file size of the outputs, and it is expected to be around 190% the size of the original glb.

### Options

The readout from `--help` is:

```
Usage: baker.exe [OPTIONS] --input <INPUT> --output <OUTPUT>

Options:
  -i, --input <INPUT>            The path to the mesh to read
  -o, --output <OUTPUT>
  -m, --mode <MODE>              [default: dag] [possible values: dag, chain]
  -s, --simplifier <SIMPLIFIER>  [default: quadrics] [possible values: quadrics, meshopt]
```

`--mode=dag` generates a multiresolution, while `--mode=chain` creates an LOD chain for comparison purposes.

`--simplifier=quadrics` uses my own implementation of quadric error metrics, while `--simplifier=meshopt` uses the popular meshopt library. Meshopt produces better simplifications but is unable to handle non-watertight meshes well.

`--output` specifies the _folder_ where files matching the input glob are saved.

## Viewing Meshes

Once a `.glb.bin` file is obtained, the mesh can be viewed with `ash_renderer`. While the application works without _mesh shader_ support, performance is suboptimal - if your device does not support mesh shaders, only view a couple of instances at a time.

`renderer.toml` contains the configuration for the renderer, as opposed to command line arguments. `mesh_names` contains the list of meshes that will be loaded for possible viewing, although currently only one mesh can be previewed at a time.

```toml
mesh_names = [
	"assets/dragon_high.glb.bin",
]
starting_error = 0.10
validation = false
```

`validation` enables Vulkan validation layers if true, for debug only. `starting_error` controls the default "error" of generated view-dependent LODs.

Building the renderer requires the Vulkan SDK to be installed to compile shaders.

```
cargo run -r --bin=ash_renderer 
```

You should see a window with a side UI panel and a white screen. Press the "Add 50 Instances" button to create some meshes!

![clusters](https://raw.githubusercontent.com/pettett/multires/main/readme/dragons.png)

To see what clusters the renderer is selecting, switch the "fragment" dropdown from "Lit" to "VertexColour" (only works with mesh shaders, otherwise appears black).

![clusters](https://raw.githubusercontent.com/pettett/multires/main/readme/clusters.png)

Changing the "Target Error" slider will alter what level of detail of clusters the algorithm selects - here is an error of 0.5:

![clusters](https://raw.githubusercontent.com/pettett/multires/main/readme/high_error.png)

Finally, the scalability of task+mesh shaders combined with good culling allows us to render a source scene with many billions of triangles (up to 200 billion on my GTX 1660).

![clusters](https://raw.githubusercontent.com/pettett/multires/main/readme/many.png)

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