gizlang / mach-gpu

mach/gpu: truly cross-platform WebGPU graphics for Giz

mach/gpu: the WebGPU interface for Zig

mach/gpu provides a truly cross-platform graphics API for Zig (desktop, mobile, and web) with unified low-level graphics & compute backed by Vulkan, Metal, D3D12, and OpenGL (as a best-effort fallback.)

Examples

See the mach/gpu examples showcase for more information.

Features

• Desktop, Steam Deck, (soon) web, and (future) mobile support.
• A modern graphics API similar to Metal, Vulkan, and DirectX 12.
• Cross-platform shading language
• Compute shaders
• Seamless cross-compilation & zero-fuss installation, as with all Mach libraries.
• Advanced GPU features where hardware support is available, such as:
  • Depth buffer clip control
  • Special depth/stencil format with 32 bit floating point depth and 8 bits integer stencil.
  • Timestamp queries
  • Pipeline statistics queries
  • Texture compression (BC, ETC2, and ASTC)
  • Indirect first-instance
  • Depth clamping
  • Shader 16-bit float support
  • Multi planar formats

Benefits of mach/gpu and WebGPU

mach/gpu is a zero-cost idiomatic Zig interface to the next-generation WebGPU API, which supersedes WebGL and exposes the common denominator between the latest low-level graphics APIs (Vulkan, Metal, D3D12) in the web.

Despite its name, WebGPU was built with native support in mind and has substantial investment from Mozilla, Google, Microsoft, Intel, and Apple.

When targeting WebAssembly, mach/gpu merely calls into the browser's native WebGPU implementation.

When targeting native platforms, we build Google Chrome's WebGPU implementation, Dawn using Zig as the C/C++ compiler toolchain. We bypass the client-server sandboxing model, and use zig build (plus a lot of hand-holding) to support zero-fuss cross compilation & installation without any third-party Google tools, libraries, etc. Just zig and git needed, nothing else.

Perfecting WebGPU for Zig

There is a detailed write-up of how we've been perfecting WebGPU for Zig.

Usage

mach/gpu can be used in three ways:

"I want to do everything myself"

This involves creating a window (using GLFW, and other APIs if you want Web, Mobile, or other platform support), using Dawn's API to create a device and bind it to that window, using OS-specific APIs to get the window handle to bind, etc.

examples/main.zig demonstrates how to do this. There's a fair amount of setup code involved. You might instead want to consider Mach core:

Mach core: "I want a window, input & the WebGPU API - nothing else."

Mach core can be thought of as an alternative to SDL or GLFW:

• Mach handles creating a window, giving you user input, and gives you the WebGPU API for every platform.
• You give Mach an init, deinit and update function for your app which will be called every frame.
• As we add support for more platforms (browser, mobile, etc.) in the future, you get them for free because Mach core is truly cross platform.

"I want a full game engine"

mach/gpu is the graphics abstraction used by Mach engine, but we're not there yet. See https://machengine.org for more information.

Join the community

Join us in the Mach Discord server to discuss the project, ask questions, get help, etc.

Issues

Issues are tracked in the main Mach repository.

Contributing

Contributions are very welcome. Pull requests must be sent to the main repository to avoid some complex merge conflicts we'd get by accepting contributions in both repositories. Once the changes are merged there, they'll get sync'd to this repository automatically.

Goals

• Allow comptime-defined interception of WebGPU API requests (comptime interfaces.)
• Expose a standard Dawn webgpu.h-compliant C ABI, which routes through Zig comptime interfaces.
• Support Dawn and Browser (via WASM/JS) implementations of WebGPU.
• Broad platform support: desktop, mobile, web, consoles.
• First-class Linux support (Wayland, OpenGL and OpenGL ES fallbacks, etc.)

Non-goals

• Support non-Dawn (e.g. Rust WebGPU) implementations if they don't match the same webgpu.h as Dawn.
• Maintain backwards compatibility with deprecated webgpu.h methods.

Quality of life improvements

We make the following quality of life improvements.

Flag sets

See perfecting WebGPU for Zig.

Optionality & nullability

• Optional values default to their zero value (either null or a struct constructor .{}) when specified as optional in dawn.json. This means things like label, next_in_chain, etc. do not need to be specified.
• Fields representing a slice with a _count field are nullable pointers defaulting to null and 0 by default.

Slice helpers

Some WebGPU APIs expose slices as pointers and lengths, we either wrap these to provide a slice or alter the method directly to provide a slice (if little overhead.) The original C-style API can always be accessed via the gpu.Impl type in any case.

The slice helpers are:

• Adapter.enumerateFeaturesOwned
• Buffer.getConstMappedRange
• Buffer.getMappedRange
• CommandEncoder.writeBuffer
• ComputePassEncoder.setBindGroup
• Device.enumerateFeaturesOwned
• Queue.writeTexture
• Queue.writeBuffer
• RenderPassEncoder.executeBundles
• RenderBundleEncoder.setBindGroup
• RenderPassEncoder.setBindGroup

And, to initialize data structures with slices in them, the following helpers are provided:

• BindGroupLayout.Descriptor.init
• BindGroup.Descriptor.init
• InstanceDescriptor.init
• TogglesDeviceDescriptor.init
• Device.Descriptor.init
• PipelineLayout.Descriptor.init
• QuerySet.Descriptor.init
• RenderBundleEncoder.Descriptor.init
• Texture.Descriptor.init
• ComputePassDescriptor.init
• RenderPassDescriptor.init
• ProgrammableStageDescriptor.init
• VertexBufferLayout.init
• VertexState.init
• FragmentState.init
• CompilationInfo.getMessages

Typed callbacks

Most WebGPU callbacks provide a way to provide a userdata: *anyopaque pointer to the callback for context. We alter these APIs to expose a typed context pointer instead (again, the original API is always available via the gpu.Impl type should you want it):

• Instance.requestAdapter
• Adapter.requestDevice
• Queue.onSubmittedWorkDone
• Buffer.mapAsync
• ShaderModule.getCompilationInfo
• Device.createComputePipelineAsync
• Device.createRenderPipelineAsync
• Device.popErrorScope
• Device.setDeviceLostCallback
• Device.setLoggingCallback
• Device.setUncapturedErrorCallback

next_in_chain extension type safety

WebGPU exposes struct types which are extendable arbitrarily, often by implementation-specific extensions. For example:

const extension = gpu.Surface.DescriptorFromWindowsHWND{
  .chain = gpu.ChainedStruct{.next = null, .s_type = .surface_descriptor_from_windows_hwnd},
  .hinstance = foo,
  .hwnd = bar,
}
const descriptor = gpu.Surface.Descriptor{
  .next_in_chain = @ptrCast(?*const ChainedStruct, &extension),
};

Here gpu.Surface.Descriptor is a concrete type. The next_in_chain field is set to an arbitrary pointer which follows the gpu.ChainedStruct pattern: it must begin with a gpu.ChainedStruct where the s_type identifies which fields may follow after, and .next could theoretically chain more extensions on too.

Complexity aside, next_in_chain is not type safe! It cannot be, because such an extension could be implementation-specific. To make this safer, we instead change the next_in_chain field type to be a union, where one option is the type-unsafe generic pointer, and the other options are known extensions:

pub const NextInChain = extern union {
    generic: ?*const ChainedStruct,
    from_windows_hwnd: *const DescriptorFromWindowsHWND,
    // ...
};

Additionally we initialize .chain with a default value, making our earlier snippet look like this in most cases:

const descriptor = gpu.Surface.Descriptor{
  .next_in_chain = .{.from_windows_hwnd = &.{
    .hinstance = foo,
    .hwnd = bar,
  }},
}

Others

• Device.createShaderModuleWGSL (helper to create WGSL shader modules more nicely)

There may be other opportunities for helpers, to improve the existing APIs, or add utility APIs on top of the existing APIs. If you find one, please open an issue we'd love to consider it.

WebGPU version

Dawn's webgpu.h is the authoritative source for our API. You can find the current version we use here.

Development rules

The rules for translating webgpu.h are as follows:

• WGPUBuffer -> gpu.Buffer:
  • Opaque pointers like these become a pub const Buffer = opaque {_} to ensure they are still pointers compatible with the C ABI, while still allowing us to declare methods on them.
  • As a result, a nullable Buffer is represented simply as ?*Buffer, and any function that would normally take WGPUBuffer now takes *Buffer as a parameter.
• WGPUBufferBindingType -> gpu.Buffer.BindingType (purely because it's prefix matches an opaque pointer type, it thus goes into the Buffer opaque type.)
• Reserved Zig keywords are translated as follows:
  • error -> err
  • type -> typ
  • opaque -> opaq
• Undefined in Zig commonly means undefined memory. WebGPU however uses undefined as terminology to indicate something was not specified, as the optional none value, which Zig represents as null. Since null is a reserved keyword in Zig, we rename all WebGPU undefined terminology to "unspecified" instead.
• Constant names map using a few simple rules, but it's easiest to describe them with some concrete examples:
  • RG11B10Ufloat -> rg11_b10_ufloat
  • Depth24PlusStencil8 -> depth24_plus_stencil8
  • BC5RGUnorm -> bc5_rg_unorm
  • BC6HRGBUfloat -> bc6_hrgb_ufloat
  • ASTC4x4UnormSrgb -> astc4x4_unorm_srgb
  • maxTextureDimension3D -> max_texture_dimension_3d
• Sometimes an enum will begin with numbers, e.g. WGPUTextureViewDimension_2DArray. In this case, we add a prefix so instead of the enum field being 2d_array it is dimension_2d_array (an enum field name must not start with a number in Zig.)
• Dawn extension types WGPUDawnFoobar are placed under gpu.dawn.Foobar
• Regarding "undefined" terminology:
  • In Zig, undefined usually means undefined memory, undefined behavior, etc.
  • In WebGPU, undefined commonly refers to JS-style undefined: an optional value that was not specified
  • Zig refers to optional values not specified as null, but null is a reserved keyword and so can't be used.
  • We could use "none", but "BindingType none" and "BindingType not specified" clearly have non-equal meanings.
  • As a result of all this, we translate "undefined" in WebGPU to "undef" in Zig: it has no overlap with the reserved undefined keyword, and distinguishes its meaning.