SDL3 new GPU API merged

https://github.com/libsdl-org/SDL/pull/9312

by caspar • 2 years ago

306 122 2 years ago

caspar4• 2 years ago

SDL3 is still in preview, but the new GPU API is now merged into the main branch while SDL3 maintainers apply some final tweaks.

As far as I understand: the new GPU API is notable because it should allow writing graphics code & shaders once and have it all work cross-platform (including on consoles) with minimal hassle - and previously that required Unity or Unreal, or your own custom solution.

WebGPU/WGSL is a similar "cross-platform graphics stack" effort but as far as I know nobody has written console backends for it. (Meanwhile the SDL3 GPU API currently doesn't seem to support WebGPU as a backend.)

shmerl2• 2 years ago

Why is SDL API needed vs gfx-rs / wgpu though? I.e. was there a need to make yet another one?

modeless• 2 years ago

The more the merrier if you ask me. Eventually one will win but we need more experimentation in this space. The existing GPU APIs are too hard to use and/or vendor-specific.

adrift• 2 years ago

Having a C API like that is always nice. I don't wanna fight Rust.

throwup238• 2 years ago

SDL the library is over a quarter century old. It powers tons of existing software. Why wouldn't people keep working on it?

dottrap4• 2 years ago

The old SDL 2D API was not powerful enough. It was conceived in the rectangle sprite blitting days, when video hardware was designed very differently and had drastically different performance characteristics. If you wanted anything more, OpenGL used to be 'the best practice'. But today, the landscape competes between Vulkan, Metal, and Direct3D, and hardware is centered around batching and shaders. Trying to target OpenGL is more difficult because OpenGL fragmented between GL vs. GLES and platform support for OpenGL varies (e.g. Apple stopped updating GL after 4.1).

A good example demonstrating where the old SDL 2D API is too limited is with the 2D immediate mode GUI library, Nuklear. It has a few simple API stubs to fill in so it can be adapted to work with any graphics system. But for performance, it wants to batch submit all the vertices (triangle strip). But SDL's old API didn't support anything like that.

The reluctance was the SDL maintainers didn't want to create a monster and couldn't decide where to draw the line, so the line was held at the old 2D API. Then a few years ago, a user successfully changed the maintainers' minds after writing a demonstration showing how much could be achieved by just adding a simple batching API to SDL 2D. So that shifted the mindset and led to this current effort. I have not closely followed the development, but I think it still aims to be a simple API, and you will still be encouraged to pick a full blown 3D API if you go beyond 2D needs. But you no longer should need to go to one of the other APIs to do 2D things in modern ways on modern hardware.

badsectoracula4• 2 years ago

SDL provides various "backend agnostic" APIs for a variety of needs, including window creation, input (with a gamepad abstraction), audio, system stuff (e.g. threads), etc so that programs written against SDL can work on a variety of systems - and if linked against it dynamically (or using the "static linking but with a dynamic override" that allows a statically linked version to use a newer dynamic version of the library) can use newer/better stuff (which is sometimes needed, e.g. some older gaming using old version of SDL1.x need the DLL/.so replaced to a new version to work on new OSes, especially on Linux).

Exposing a modern (in the sense of how self-proclaimed modern APIs like Vulkan, D3D12 and Metal work) GPU API that lets applications written against it to work with various backends (D3D11, D3D12, Vulkan, Metal, whatever Switch and PS5 uses, etc) fits perfectly with what SDL already does for every other aspect of making a game/game engine/framework/etc.

As if it was "needed", it was needed as much as any other of SDL's "subsystems": strictly speaking, not really as you could use some other library (but that could be said for SDL itself) but from the perspective of what the SDL wants to provide (an API to target so you wont have to target each underlying API separately) it was needed for the sake of completeness (previously OpenGL was used for this task if you wanted 3D graphics but that was when OpenGL was practically universally available for the platforms SDL itself officially supported - but nowadays this is not the case).

TinkersW• 2 years ago

WebGPU would be alot more useful if it hadn't gone with such a needlessly different shader language syntax, makes it much harder to have any single src between the C++ and it.

WhereIsTheTruth2• 2 years ago

SDL is for gamedevs, it supports consoles, wgpu is not, it doesn't

flohofwoe6• 2 years ago

While WebGPU isn't a bad API, it also isn't exactly the '3D API to end all 3D APIs'.

WebGPU has a couple of design decisions which were necessary to support Vulkan on mobile devices, which make it a very rigid API and even (desktop) Vulkan is moving away from that rigid programming model, while WebGPU won't be able to adapt so quickly because it still needs to support outdated mobile GPUs across all operating systems.

flohofwoe6• 2 years ago

One important point I haven't seen mentioned yet is that SDL is the defacto minimal compatibility layer on Linux for writing a windowed 'game-y' application if you don't want to directly wrestle with X11, Wayland, GTK or KDE.

dxuh• 2 years ago

Unreal/Unity are not the only solutions. There is also bgfx (https://github.com/bkaradzic/bgfx), which is quite popular and sokol gfx (https://github.com/floooh/sokol) which I know of. Of course there are many more lesser known ones.

jcelerier• 2 years ago

Qt RHI too. Shaders are normal vulkan-compatible GLSL and then you get D3D11, 12, GL and Metal

klaussilveira2• 2 years ago

There is NVIDIA's NVRHI:

https://github.com/NVIDIAGameWorks/nvrhi

benlwalker• 2 years ago

Compared to libraries like bgfx and sokol at least, I think there are two key differences.

1) SDL_gpu is a pure C library, heavily focused on extreme portability and no depedencies. And somehow it's also an order of magnitude less code than the other options. Or at least this is a difference from bgfx, maybe not so much sokol_gfx.

2) The SDL_gpu approach is a bit lower level. It exposes primitives like command buffers directly to your application (so you can more easily reason about multi-threading), and your software allocates transfer buffers, fills them with data, and kicks off a transfer to GPU memory explicitly rather than this happening behind the scenes. It also spawns no threads - it only takes action in response to function calls. It does take care of hard things such as getting barriers right, and provides the GPU memory allocator, so it is still substantially easier to use than something like Vulkan. But in SDL_gpu it is extremely obvious to see the data movements between CPU and GPU (and memory copies within the CPU), and to observe the asynchronous nature of the GPU work. I suspect the end result of this will be that people write far more efficient renderers on top of SDL_gpu than they would have on other APIs.

runevault2• 2 years ago

Worth noting Godot also has cross platform shaders. Its GDShader language is based heavily on OpenGL shader language though not a 1:1 copy and gets compiled for the target platform. Though for PS5 and XBox you have to work with a 3rd party (Someone released the Nintendo build for anyone who's signed the Nintendo NDA).

jb19912• 2 years ago

SDL is also offering cross platform GPU compute, is that also available in Godot?

bgbernovici• 2 years ago

I previously integrated bgfx [1], which allows you to write graphics code and shaders once and supports consoles, with SDL2 stack and Swift [2]. It was quite a nice experience, especially for someone who had never worked with any of these tools before. I'm excited for SDL3 as it introduces console abstractions, eliminating the need for additional dependencies for the GPU API. Moreover, Godot officially supports the Steam Deck, and hopefully, more consoles will be supported in the future. On a related note, Miguel de Icaza is advocating for Swift adoption in Godot, and he is working on porting the editor to SwiftUI on iPad. It is interesting to see the progress [3].

[1] https://bkaradzic.github.io/bgfx/overview.html

[2] https://github.com/bgbernovici/myndsmith

[3] https://blog.la-terminal.net/xogot-code-editing/

quadhome• 2 years ago

More context here: https://icculus.org/finger/flibitijibibo?date=2024-06-15&tim...

stateoff2• 2 years ago

This article from the main author of the API describes how the buffer cycling works: https://moonside.games/posts/sdl-gpu-concepts-cycling/

kvark2• 2 years ago

This rubs me the wrong way. Resource renaming is a high level concept, which was one of the features of OpenGL that all the modern APIs have successfully dropped. A modern low level GPU API should not do that.

davikr• 2 years ago

Are there any examples?

stateoff2• 2 years ago

Examples will be based on this repo, I believe: https://github.com/TheSpydog/SDL_gpu_examples

immibis• 2 years ago

Feels like SDL3 suffers the second system effect. (SDL2 was just SDL1 with explicit window handles, so SDL3 is the second system, not the third). SDL1/2 is a thin layer that wraps the platform-specific boilerplate of opening a window and handling input events, so you can get to the OpenGL rendering stuff that you actually wanted to write.

caspar4• 2 years ago

If you only want to support Windows/Linux/Android, then sure, you can definitely argue that the SDL GPU API is bloat.

But if you want to support Apple's operating systems then you're stuck with OpenGL 4.1 (officially deprecated by Apple 5 years ago) - so no modern GPU features like compute shaders.

You can go the Vulkan route and use MoltenVK for Apple systems, but Vulkan is quite a step up in complexity from OpenGL ("1000 lines of code for a triangle" as people like to say). The goal for SDL3's GPU API is to give you a more approachable (but still plenty flexible) alternative to that.

And similar story for consoles, presumably.

Apparently lots of people asked for "SDL_render but can you add shader support that works for all platforms", so that's the origin story.

SDL3 does also add a higher level audio API - I don't know much about its merits.

caspar4• 2 years ago

Ah, I managed to dig up the original announcement post[0]; relevant snippet:

But this is terrible advice in 2021, because OpenGL, for all intents and purposes, is a deprecated API. It still works, it's still got some reasonably modern features, but even if you add up the 22 years Microsoft spent trying to kill it with Apple's seven-or-maybe-twenty, it doesn't change the fact that the brains behind OpenGL would rather you migrate to Vulkan, which is also terrible advice.
It seems bonkers to tell people "write these three lines of code to make a window, and then 2000 more to clear it," but that's the migration funnel--and meat grinder--that SDL users are eventually going to get shoved into, and that's unacceptable to me.

[0] https://www.patreon.com/posts/new-project-top-58563886

hgs3• 2 years ago

But why does the GPU API need to be in mainline SDL? Couldn't it be a separate project like SDL_net, SDL_mixer, SDL_image, and SDL_ttf? I would think that as a separate project "SDL_gpu" could be versioned independently, evolve independently, and not be obligated to support every platform SDL itself supports. In fact if "SDL_gpu" only required a windowing context, then it could presumably integrate with SDL2 and non-SDL applications!

creata• 2 years ago

Slightly off-topic, but where's the complexity of Vulkan (the 1000 lines) coming from? My memory tells me that most of the misery is from the window system integration, and that the rest is pretty pleasant.

gary_04• 2 years ago

SDL2 was not "just SDL1 with explicit window handles". There were a variety of changes and new features all over the API, including (like SDL3) major changes to the graphics subsystem (SDL1 used software rendering, SDL2 added hardware acceleration).

Also, SDL2 has evolved considerably since 2.0.0, and SDL3 continues that evolution while allowing API-breaking changes. SDL3 is not a from-scratch re-write and as an SDL user I dont anticipate migrating from SDL2 to SDL3 will be that difficult.

[edit] And SDL1/2 was never so "thin" that it didn't have its own high-level graphics system, which is useful to have out-of-the-box so that new/basic users can get stuff on screen right away.

[edit2] As ahefner points out, SDL1 was pretty "thin" by modern standards, but it still gave you enough to draw basic stuff on screen without writing your own pixel math, which was pretty helpful back in the 90's.

ahefner• 2 years ago

SDL1 had no high-level graphics system - you either got a raw framebuffer, or an OpenGL context.

flohofwoe6• 2 years ago

The problem is that OpenGL is (pretty much) dead, while Vulkan is a poor replacement for OpenGL when it comes to ease of use.

sylware• 2 years ago

I don't run GL games anymore on elf/linux. And it has been a while. Most cross-platform game engines have a vulkan backend now.

Very small teams are able to show games running the latest UE5.x engine on native elf/linux, vulkan ("vein", "shmaragon" something).

But the steam client... is still 32bits and x11/GL hard dependent...

I still plan to code my own wayland compositor once the steam client is ELF64 and does proper wayland->x11/vulkan->CPU fallbacks. It will feel weird to have a clean 64bits system.

shortrounddev22• 2 years ago

Yeah, there needs to be a DirectX 11-like API between Vulkan an OpenGL

account425• 2 years ago

The render API was already needless bloat for many SDL users. SDL2 was also significantly larger than SDL1 in binary size already.

This abstraction at least has the potential to fulfil the needs of anything more than simple 2D games while allowing you to target the sadly increasingly fragmented graphics API ecosystem (RIP dreams of an universal OpenGL(Next) future). Looks like the hardest part (shader translation) isn't there yet though.

rudedogg• 2 years ago

It's exciting to see how this all shakes out. Hopefully we end up with more options for building custom game engines and apps.

I've been going down the Vulkan rabbit hole. It's been fun/enlightening to learn, but the nature of Vulkan makes progress feel slow. I think if SDL3 were available when I started, I would have happily went that route and have more to show for the amount of time I've invested.

jb19912• 2 years ago

I’ve never used this library before, but I’m very interested to see some examples of its cross-platform GPU compute abilities, if I understand from the link thread that they are now available. Does anyone have a suggestion on where to get started?

bni• 2 years ago

Is this related to https://github.com/grimfang4/sdl-gpu ? Or is it a completely separate thing with the same name?

dottrap4• 2 years ago

This is a separate thing with the same name. Although both share some common ideas. The grimfang4/sdl-gpu is a separate library used with SDL, while the new SDL GPU API is directly part of SDL. grimfang4/sdl-gpu is much older and works with today's SDL 2.

The grimfang4/sdl-gpu was one good way to take advantage of modern GPUs in a simple way and workaround the holes/limitations of the old SDL 2D API. The new SDL 3 GPU API will likely make the need for things like grimfang4/sdl-gpu redundant.

Ono-Sendai• 2 years ago

I might try this out. SDL I have found to be high quality software - compiles fast, compiles easily on multiple platforms, always works. So I have some hopes for this new API.

ivars• 2 years ago

How did they managed to pull this off so quickly? Given how long WebGPU native is in development and still not finalized, you would think it will take SDL GPU API even longer because it supports more platforms.

bartwe2• 2 years ago

No committee and motivated devs that need the result for their projects. Especially the FNA folks.

flohofwoe6• 2 years ago

Also tbf, the WebGPU peeps did a lot of investigations for what is the actual set of common and web-safe features across D3D, Vulkan and Metal, and all those investigation results are in the open.

In that sense the WebGPU project is an extremely valuable resource for other wrapper APIs, and saves those other APIs a ton of time.

HexDecOctBin6• 2 years ago

The reason WebGPU took so long was that they decided to write their own shading language instead of using SPIR-V. SDL didn't make that mistake, you bring your own shader compilers and translation tools.

There is a sister project for a cross-platform shading language [1] and another for translating existing ones between each other [2] , but they get done when they get done, and the rest of the API doesn't have to wait for them.

WebGPU was made by a committee of vendors and language-lawyers (standards-lawyers?) with politics and bureaucracy, and it shows. SDL_GPU is made by game developers who value pragmatism above all (and often are looked down upon from the ivory tower because of that).

[1] https://github.com/libsdl-org/SDL_shader_tools [2]: https://github.com/flibitijibibo/SDL_gpu_shadercross

hmry• 2 years ago

Yeah, legal strikes again. Unfortunately SPIR-V was never going to be an option for WebGPU, because Apple refuses to use any Khronos projects due to a confidential legal dispute between them.[0] If WebGPU used SPIR-V, it just wouldn't be available in Safari.

See also: Not supporting Vulkan or OpenXR at all, using USD instead of glTF for AR content even though it's less well suited for the task, etc. (Well, they probably don't mind that it helps maintain the walled garden either... There's more than one reason for everything)

0: https://docs.google.com/document/d/1F6ns6I3zs-2JL_dT9hOkX_25...

grovesNL3• 2 years ago

I don't think that's accurate. Creating a shading language is obviously a huge effort, but there were already years of effort put into WebGPU as well as implementations/games building on top of the work-in-progress specification before the shading language decision was made (implementations at the time accepted SPIR-V).

kg• 2 years ago

The core contributors of the SDL3 GPU project have experience with two cross-platform (PC + consoles) GPU abstraction layers, FNA3D and Refresh, which provided a lot of knowledge and existing open source code to use as a springboard to assemble this quickly with high quality.

account425• 2 years ago

Simple: SDL GPU left out the rest of the owl (translating shaders from a common format to API-specific intermediates).

bartwe2• 2 years ago

Glad to have contributed to the dx12 part :)

HexDecOctBin6• 2 years ago

Bravo, thanks! Since I'll be targeting modern HLSL, your backend is the one I'll be using to begin with. Hopefully DXC produces decent SPIR-V at the end.

corysama• 2 years ago

What resources would you recommend for learning DX12?

JoeyJoJoJr• 2 years ago

I’d love to see Raylib get an SDL GPU backend. I’d pick it up in a heartbeat.

westurner7• 2 years ago

raylib > "How to compile against the [SDL2] backend" https://github.com/raysan5/raylib/discussions/3764

ammar-DLL• 2 years ago

i'm looking forward to wayland native support

kookamamie2• 2 years ago

Sorry, but the proposal for the included shading language looks pretty braindead to me.

See for yourself: https://github.com/libsdl-org/SDL_shader_tools/blob/main/doc...

Deviations from C-language families, such as "Flow control statements don't need parentheses." are completely unnecessary, I think. Same goes for "Flow control statements must use braces."

mahkoh• 2 years ago

If control flow statements don't require parentheses to be parseable, doesn't that mean that it is the parentheses that are completely unnecessary?

BigJono• 2 years ago

Deviating from conventions to avoid footguns is so misguided. I've been writing C family languages for like 15 years and never once accidentally done a if (foo); whatever;

The convention itself IS the thing that stops you from fucking that up. It's the kind of thing you do once 2 days into a 30 year career and never again.

I still think it's dumb in Javascript, where you could be using the language on day 2 of learning programming. But in a GPU shader language that it would be almost impossible to understand with no programming experience? It's actually insane.

Having said that everything else about this project looks pretty good, so I guess they can get a pass lol.

e4m22• 2 years ago

The current SDL GPU API does not intend to use this shader language. Instead, users are expected to provide shaders in the relevant format for each underlying graphics API [1], using whatever custom content pipeline they desire.

One of the developers made an interesting blog post motivating this decision [2] (although some of the finer details have changed since that was written).

There is also a "third party" solution [3] by another one of the developers that enables cross-platform use of SPIR-V or HLSL shaders using SPIRV-Cross and FXC/DXC, respectively (NB: It seems this currently wouldn't compile against SDL3 master).

[1] https://github.com/libsdl-org/SDL/blob/d1a2c57fb99f29c38f509...

[2] https://moonside.games/posts/layers-all-the-way-down

[3] https://github.com/flibitijibibo/SDL_gpu_shadercross

kookamamie2• 2 years ago

Thanks for the clarification. From the sparse documentation of SDL_GPU it was somewhat difficult to understand which parts are part of the SDL 3 merge, and which parts are something else.

I did find an example of using the GPU API, but I didn't see any mention of selecting a backend (Vk, etc.) in the example - is this possible or is the backend selected e.g. based on the OS?

dkersten• 2 years ago

I, on the other hand, find the C way brain dead and would be very happy with these changes.

JKCalhoun• 2 years ago

Huge fan of SDL generally.

When I went looking for a cross-platform gaming library, SDL and its API struck the right balance for me. I just wanted a C (++) library I could call to create windows and graphical contexts — a fast sprite rendering framework. I didn't need a whole IDE or a bloated library, didn't want to learn a new language, etc.

kvark2• 2 years ago

Time will tell if this API is usable. In particular, the way resource synchronization works, and object renaming. Time will tell if it will perform better than WebGPU or other abstractions. Time will tell if it remains small in the presence of driver bugs that need working around…

I’m also sceptical about their new bytecode for a shading language. Parsing shaders at runtime was not a concern with WebGPU - it’s very fast. Even producing native shaders is fast [1]. It’s the pipeline creation that’s slow, and this bytecode wouldn’t help here.

[1] http://kvark.github.io/naga/shader/2022/02/17/shader-transla...

SDL3 new GPU API merged

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