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A Guide to Rust Graphics Libraries as of 2019
- chubs 7y agoGreat write-up! I'd really like to know how gfx-hal handles shaders. Do you write shaders in some high-level language, and gfx translates them appropriately for the vulkan/metal/dx backends, and send them off to the GPU driver? If so, is this transpiling slow? Do you get slightly different visuals on different backends? Or even glitches on some? Thanks for the write-up :)
- robmaister 7y agoI'm not familiar with the specifics within gfx-hal, but it's most likely taking in SPIR-V and translating as needed. AFAIK DX12 still requires DXIL so it might be saving both SPIR-V and DXIL, or taking in HLSL and compiling/translating as needed. Microsoft has generally gotten a lot friendlier in the last decade, they have tools to compile HLSL down to SPIR-V, if you want to support everything including DX12 you'll probably be writing HLSL. Otherwise you can pick any language that compiles down to SPIR-V. https://github.com/Microsoft/ShaderConductor https://github.com/Microsoft/ShaderConductor https://github.com/KhronosGroup/SPIRV-Cross https://github.com/KhronosGroup/SPIRV-Cross
- chubs 7y agoSo from what I can find, it seems gfx-hal works with GLSL, compiles it to SPIRV, and then uses that (somehow). I'm just not sure how it uses the SPIRV for each backend.
- robmaister 7y agoThe first link I included has a wonderful diagram of this (but from the perspective of HLSL instead of GLSL), the gist of it is: GLSL gets compiled to SPIR-V ahead of time by a compiler of your choice (probably glslangValidator). You can take that binary blob and feed it into Vulkan (vkCreateShaderModule) or OpenGL (glShaderBinary as long as you have the right extension). For everything else, Khronos has a tool called SPIRV-Cross (second link), which reads the SPIR-V binary data and emits a text file/string in ESSL for OpenGL ES, MSL for Metal, or HLSL for DirectX <=11. Those all go through the "normal" paths for loading shader code in their own APIs.
- chubs 7y agoThanks so much for explaining how that works :) Is it just me or does decompiling the binary SPIR-V to ESL/HLSL source code then recompiling sound like a recipe for massive inefficiency? Or in practice does it work out pretty nicely?
- robmaister 7y agoYes, it's absolutely inefficient but for those platforms it's the only way to execute your own code on the GPU. Metal has a bitcode format that I know nothing about and I believe older DirectX had some intermediate format that was binary. Both are proprietary and only documented via reverse-engineering, so they're not great targets. Most of the extra cost of feeding in SPIR-V could also be offset if you generate the text shader code at compile/packaging time so that those builds don't have the original SPIR-V in them.
- kvark 7y agoIt's not absolutely impossible. DXBC was well reverse engineered, and DXIL could also be a direct target for translation. It's up to future work, which for us also includes writing an in house shader converter as a substitute to SPIRV-Cross. This isn't a big concern at the moment though, since most of the shader loading/compiling time is spent by the driver receiving the result, not us translating it. Generating a text shader at packaging time is certainly an option to explore, especially for self-contained users like WebRender. The trouble here is that we adjust the shader code based on the pipeline and pipeline layout, so we can only really start translation at the run/init time, unless we start pre-packaging a set of "popular" configurations (which is feasible for WebRender).
- kvark 7y agoThe API works off SPIRV, it doesn't know anything about GLSL. The latter is only used by the examples for convenience.
- rossy 7y agoTake another look at SPIRV-Cross. It's a C++ library that can convert SPIR-V to HLSL, MSL or legacy GLSL/ESSL. I'm not too familiar with Rust or gfx, but it seems like the dx11, dx12, metal and gl backends reference the spirv_cross crate, so that's probably what it's using. To try to answer your original question, I've never used gfx, but we use SPIRV-Cross in mpv to translate video processing shaders written in GLSL to HLSL for Direct3D 11, and it works quite well. Modern GLSL and HLSL seem to be pretty similar, apart from using different coordinate systems. Most HLSL concepts directly map to a GLSL concept (eg. GLSL UBOs become HLSL cbuffers, etc.) Shader translation with SPIRV-Cross definitely isn't the slowest part of our shader compilation pipeline, either. D3DCompile is much slower.
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- mikekchar 7y agoBTW, I just wanted to give a shout out to ggez (the author's game library). I've been playing with it and it's quite a lot of fun to use. I'm a novice in Rust and I found it to be quite a nice introduction to the language. There are a couple of bugs here and there, but pretty much it does what's printed on the box. Very nice documentation and lots of examples to work with too. And the cherry on the cake is raising an issue is a welcoming rather than harrowing experience. You get the feeling that whatever issues might crop up, you can work your way through them. Edit: grammar
- shepmaster 7y agoIf you are interested in hearing more from the author of ggez, check out their talk from Rust Belt Rust 2018: - Evolving API design in Rust — Simon Nicholas Heath (https://www.youtube.com/watch?v=Xt1JOVeQ5hw https://www.youtube.com/watch?v=Xt1JOVeQ5hw)
- icefoxen 7y agoHi, author here, happy to answer any questions people have.
- young_unixer 7y ago>OpenGL: Basically Javascript for GPU’s. Everyday we stray further from god's light.
- jjtheblunt 7y agoYeah, that comment you cited is unbelievably misinformed.
- rossy 7y agoI had a visceral reaction to that sentence too, but read the rest of the paragraph. It's not wrong in the way the author meant it. The author is saying that OpenGL is like JavaScript because it's high level, it's open and supported everywhere, it was designed in the 90s in a very different ecosystem to what we have today, and even though it's been updated and the old versions are no longer worth using (ECMAScript 3 and OpenGL 2.1,) the new versions still have a bunch of weird historical baggage. I don't see anything wrong with that.
- slezyr 7y agoIs it? Implementation of OpenGL basically a browser. It's a virtual machine that executes GLSL with garbage collector and other quirky stuff.
- sanderjd 7y agoUpvoted for the poetry. Thanks :)
- _bxg1 7y agoVery good deep-dive, but I'm surprised there was little mention of the higher-level libraries that do exist already. I've found kiss3d and three-rs, both of which seem pretty early but appear to let you "load a model you made in Blender and show it on screen".
- rezeroed 7y agoKiss3d is great. It has some rendering issues on mac, but a great level of abstraction.
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- Shikadi 7y ago>OpenGL: Basically the Javascript of graphics API’s. Not trying to be rude, but I'd just like to point out the apostrophe on API's indicates ownership, as in "John's dog jumped". APIs is fine, as in "John has two dogs".
- YohAsakura 7y agoThank you very much for such detailed explanation of what is what in the world of graphics, now I understand the basics and what all the cool words (metal, gfx-hal, opengl, etc.) mean.