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gpu: use Dawn adapter creation API for now so that GPU_BACKEND selection works

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`webgpu.h` does not expose a method of choosing the GPU backend (vulkan, opengl, opengles, etc.)
at present. The only way to achieve this is to use Dawn's C++ API, which we expose as C shims
under the `machDawnNative*` prefix.

For now, we will use the Dawn adapter creation API so that we can choose between Vulkan/OpenGL/OpenGLES
etc via the `GPU_BACKEND` env var.

In the future, I believe we can do something nicer here. For example, perhaps we extend our `requestAdapter`
method (after all, we do not need to strictly match `webgpu.h`) to take such an option and be Dawn-aware so
that it handles this more seamlessly behind the scenes.

Fixes https://github.com/hexops/mach/issues/192#issuecomment-1080895255

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
This commit is contained in:
Stephen Gutekanst 2022-03-31 16:51:48 +00:00
parent 1f076da7bf
commit fbbb0b0ae0
1 changed files with 34 additions and 10 deletions
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44
gpu/examples/sample_utils.zig
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@ -67,21 +67,45 @@ pub fn setup(allocator: std.mem.Allocator) !Setup {
const instance = c.machDawnNativeInstance_init();
var native_instance = gpu.NativeInstance.wrap(c.machDawnNativeInstance_get(instance).?);
const gpu_interface = native_instance.interface();
// Discovers e.g. OpenGL adapters.
try discoverAdapters(instance, window, backend_type);
// Request an adapter.
const backend_adapter = switch (gpu_interface.waitForAdapter(&.{
.power_preference = .high_performance,
})) {
.adapter => |v| v,
.err => |err| {
std.debug.print("failed to get adapter: error={} {s}\n", .{ err.code, err.message });
std.process.exit(1);
},
};
//
// TODO: It would be nice if we could use gpu_interface.waitForAdapter here, however the webgpu.h
// API does not yet have a way to specify what type of backend you want (vulkan, opengl, etc.)
// In theory, I suppose we shouldn't need to and Dawn should just pick the best adapter - but in
// practice if Vulkan is not supported today waitForAdapter/requestAdapter merely generates an error.
//
// const gpu_interface = native_instance.interface();
// const backend_adapter = switch (gpu_interface.waitForAdapter(&.{
// .power_preference = .high_performance,
// })) {
// .adapter => |v| v,
// .err => |err| {
// std.debug.print("failed to get adapter: error={} {s}\n", .{ err.code, err.message });
// std.process.exit(1);
// },
// };
const adapters = c.machDawnNativeInstance_getAdapters(instance);
var dawn_adapter: ?c.MachDawnNativeAdapter = null;
var i: usize = 0;
while (i < c.machDawnNativeAdapters_length(adapters)) : (i += 1) {
const adapter = c.machDawnNativeAdapters_index(adapters, i);
const properties = c.machDawnNativeAdapter_getProperties(adapter);
const found_backend_type = @intToEnum(gpu.Adapter.BackendType, c.machDawnNativeAdapterProperties_getBackendType(properties));
if (found_backend_type == backend_type) {
dawn_adapter = adapter;
}
}
if (dawn_adapter == null) {
std.debug.print("no matching adapter found for {s}", .{@tagName(backend_type)});
std.debug.print("-> maybe try GPU_BACKEND=opengl ?\n", .{});
std.process.exit(1);
}
assert(dawn_adapter != null);
const backend_adapter = gpu.NativeInstance.fromWGPUAdapter(c.machDawnNativeAdapter_get(dawn_adapter.?).?);
// Print which adapter we are going to use.
const props = backend_adapter.properties;