https://github.com/expenses/transmission-renderer
A high-performance renderer to render glTF models that use the `KHR_materials_transmission` and `KHR_materials_volume` extensions.
https://github.com/expenses/transmission-renderer
gltf gltf2 rust rust-lang vulkan vulkan-api
Last synced: 1 day ago
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A high-performance renderer to render glTF models that use the `KHR_materials_transmission` and `KHR_materials_volume` extensions.
- Host: GitHub
- URL: https://github.com/expenses/transmission-renderer
- Owner: expenses
- Created: 2021-11-23T14:27:42.000Z (over 4 years ago)
- Default Branch: dodgy-tracy-support
- Last Pushed: 2022-01-25T17:11:18.000Z (over 4 years ago)
- Last Synced: 2024-04-15T23:14:06.410Z (about 2 years ago)
- Topics: gltf, gltf2, rust, rust-lang, vulkan, vulkan-api
- Language: Rust
- Homepage:
- Size: 5.78 MB
- Stars: 35
- Watchers: 4
- Forks: 0
- Open Issues: 2
-
Metadata Files:
- Readme: readme.md
Awesome Lists containing this project
README
This is a high-performance renderer designed among other things to render glTF models that use the `KHR_materials_transmission` and `KHR_materials_volume` extensions.
It can:
* Handle rough transmissive materials such as frosted glass.
* Approximate refracted light through transmissive models that specify a thickness.
* Attenuate light via Beer's law.
It wasn't easy working out how to render these models. While the [glTF extension READMEs](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_transmission) as fairly extensive, I had to look through the code of the [glTF-Sample-Viewer] to work out implementation details.
Transmissive materials that are totally smooth and do not have a volume can be rendered without any super special tricks [via pre-multiplied alpha and additive blending](https://stackoverflow.com/a/67047837/15390861). Transmissive materials with any kind of roughness or volume are quite a bit trickier.
The main trick I realised from reading over the code from the [glTF-Sample-Viewer] is that you need to render or blit all the rendered diffuse objects to a second framebuffer texture, which you then sample in a seperate pass for all the transmissive objects. If you want to handle rough transmissive objects then you need to generate a mip-chain for this sampled texture, as rougher objects need to fetch the transmitted light of the pixels behind them in a 'blurrier' way.
In my shader code, this is done via two functions (these I did mostly copy from the [gltf-Sample-Viewer]). The first, [`ibl_volume_refraction`](https://github.com/expenses/transmission-renderer/blob/0b06623e8c4e67b1cd44256cc050097dbfa169ab/glam-pbr/src/lib.rs#L290-L348) is only ran once per pixel. It handles fetching the transmitted light from the sampled framebuffer and attenuating it.
The second, the [`transmission_btdf`](https://github.com/expenses/transmission-renderer/blob/0b06623e8c4e67b1cd44256cc050097dbfa169ab/glam-pbr/src/lib.rs#L195-L231) is ran once per light and handles light that is scattered through the model and out onto the other side. This only effects materials that are a bit rough.
## Running
Clone https://github.com/KhronosGroup/glTF-Sample-Models into this directory as run with:
`cargo run -- `
```
transmission-renderer 0.1.0
USAGE:
transmission-renderer [FLAGS] [OPTIONS]
FLAGS:
--external-model Render a model external to the glTF-Sample-Models directory, in which case the full path
needs to be specified
-h, --help Prints help information
--log-leaks Log allocator leaks on shutdown. Off by default because it makes panics hard to debug
-V, --version Prints version information
OPTIONS:
--roughness-override
Override the default roughness factor of the model. Doesn't effect models that use a
texture for roughness
-s, --scale A scale factor to be applied to the model [default: 1.0]
ARGS:
The name of the model inside the glTF-Sample-Models directory to
render
```
For some cool examples:
`cargo run -- DragonAttenuation --roughness-override 0.25`
`cargo run -- IridescentDishWithOlives --scale 5`
`cargo run -- MosquitoInAmber --scale 20`
`cargo run -- AttenuationTest --scale 0.1`
## Shader Compiling
I'm using my own project, [rust-gpu-cli-builder](https://github.com/expenses/rust-gpu-cli-builder) to build the shader module as I prefer this to using a build script. The arguments that I use to build it are:
`--target spirv-unknown-spv1.3 --capabilities RuntimeDescriptorArray --extensions SPV_EXT_descriptor_indexing`
## Other Fun Stuff
Oh, it also features
* Shader written entirely in [https://github.com/EmbarkStudios/rust-gpu](rust-gpu).
* Basic frustum culling via a compute shader and `vkCmdDrawIndexedIndirectCount`.
* A depth pre-pass setup where at max 2 full screens of fragments are processed (1 screen of opaque and 1 of transmissive objects on top).
[glTF-Sample-Viewer]: https://github.com/KhronosGroup/glTF-Sample-Viewer