|author||Raph Levien <firstname.lastname@example.org>||Wed Mar 02 14:44:03 2022 -0800|
|committer||Raph Levien <email@example.com>||Mon Mar 14 16:32:08 2022 -0700|
Variable size encoding of draw objects This patch switches to a variable size encoding of draw objects. In addition to the CPU-side scene encoding, it changes the representation of intermediate per draw object state from the `Annotated` struct to a variable "info" encoding. In addition, the bounding boxes are moved to a separate array (for a more "structure of "arrays" approach). Data that's unchanged from the scene encoding is not copied. Rather, downstream stages can access the data from the scene buffer (reducing allocation and copying). Prefix sums, computed in `DrawMonoid` track the offset of both scene and intermediate data. The tags for the CPU-side encoding have been split into their own stream (again a change from AoS to SoA style). This is not necessarily the final form. There's some stuff (including at least one piet-gpu-derive type) that can be deleted. In addition, the linewidth field should probably move from the info to path-specific. Also, the 1:1 correspondence between draw object and path has not yet been broken. Closes #152
This repo contains the new prototype for a new compute-centric 2D GPU renderer.
It succeeds the previous prototype, piet-metal.
The main goal is to answer research questions about the future of 2D rendering:
Is a compute-centered approach better than rasterization (Direct2D)? How much so?
To what extent do “advanced” GPU features (subgroups, descriptor arrays) help?
Can we improve quality and extend the imaging model in useful ways?
Another goal is to explore a standards-based, portable approach to GPU compute.
Much of the research progress on piet-gpu is documented in blog entries. See doc/blogs.md for pointers to those.
There is a much larger and detailed vision that explains the longer-term goals of the project, and how we might get there.
It makes a lot of sense to use gfx-hal, as it addresses the ability to write kernel and runtime code once and run it portably. But in exploring it I‘ve found some points of friction, especially in using more “advanced” features. To serve the research goals, I’m enjoying using Vulkan directly, through ash, which I've found does a good job tracking Vulkan releases. One example is experimenting with
The hal layer in this repo is strongly inspired by gfx-hal, but with some differences. One is that we‘re shooting for a compile-time pipeline to generate GPU IR on DX12 and Metal, while gfx-hal ships SPIRV-Cross in the runtime. To access Shader Model 6, that would also require bundling DXC at runtime, which is not yet implemented (though it’s certainly possible).
The case for wgpu is also strong, but it‘s even less mature. I’d love to see it become a solid foundation, at which point I'd use it as the main integration with Druid.
In short, the goal is to facilitate the research now, collect the data, and then use that to choose a best path for shipping later.
In addition, the shaders are provided under the terms of the Unlicense. The intent is for this research to be used in as broad a context as possible.
The dx12 backend was adapted from piet-dx12 by Brian Merchant.
Contributions are welcome by pull request. The Rust code of conduct applies.