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Return an error instead of panicking when canvas context is unavailable #3052

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merged 2 commits into from
Dec 1, 2022
Merged

Return an error instead of panicking when canvas context is unavailable #3052

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b265540
Low-level error handling in canvas context creation (for WebGPU and W…
kpreid Sep 26, 2022
c28eab2
Breaking: Change type of `create_surface()` functions to expose canva…
kpreid Sep 27, 2022
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Low-level error handling in canvas context creation (for WebGPU and W… 
…ebGL 2).

Part of fixing #3017. This commit changes the handling of `web_sys`
errors and nulls from `expect()` to returning `Err`, but it doesn't
actually affect the public API — that will be done in the next commit.
  • Loading branch information
@kpreid
kpreid committed Dec 1, 2022
commit b265540f4b1fbdfa05ee69b61781afd90b957648
61 changes: 41 additions & 20 deletions wgpu-hal/src/gles/web.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,32 +33,53 @@ impl Instance {
&self,
canvas: &web_sys::HtmlCanvasElement,
) -> Result<Surface, crate::InstanceError> {
let webgl2_context = canvas
.get_context_with_context_options("webgl2", &Self::create_context_options())
.expect("Cannot create WebGL2 context")
.and_then(|context| context.dyn_into::<web_sys::WebGl2RenderingContext>().ok())
.expect("Cannot convert into WebGL2 context");

*self.webgl2_context.lock() = Some(webgl2_context.clone());

Ok(Surface {
webgl2_context,
srgb_present_program: None,
swapchain: None,
texture: None,
presentable: true,
})
self.create_surface_from_context(
canvas.get_context_with_context_options("webgl2", &Self::create_context_options()),
)
}

pub fn create_surface_from_offscreen_canvas(
&self,
canvas: &web_sys::OffscreenCanvas,
) -> Result<Surface, crate::InstanceError> {
let webgl2_context = canvas
.get_context_with_context_options("webgl2", &Self::create_context_options())
.expect("Cannot create WebGL2 context")
.and_then(|context| context.dyn_into::<web_sys::WebGl2RenderingContext>().ok())
.expect("Cannot convert into WebGL2 context");
self.create_surface_from_context(
canvas.get_context_with_context_options("webgl2", &Self::create_context_options()),
)
}

/// Common portion of public `create_surface_from_*` functions.
///
/// Note: Analogous code also exists in the WebGPU backend at
/// `wgpu::backend::web::Context`.
fn create_surface_from_context(
&self,
context_result: Result<Option<js_sys::Object>, wasm_bindgen::JsValue>,
) -> Result<Surface, crate::InstanceError> {
let context_object: js_sys::Object = match context_result {
Ok(Some(context)) => context,
Ok(None) => {
// <https://html.spec.whatwg.org/multipage/canvas.html#dom-canvas-getcontext-dev>
// A getContext() call “returns null if contextId is not supported, or if the
// canvas has already been initialized with another context type”. Additionally,
// “not supported” could include “insufficient GPU resources” or “the GPU process
// previously crashed”. So, we must return it as an `Err` since it could occur
// for circumstances outside the application author's control.
return Err(crate::InstanceError);
}
Err(js_error) => {
// <https://html.spec.whatwg.org/multipage/canvas.html#dom-canvas-getcontext>
// A thrown exception indicates misuse of the canvas state. Ideally we wouldn't
// panic in this case, but for now, `InstanceError` conveys no detail, so it
// is more informative to panic with a specific message.
panic!("canvas.getContext() threw {js_error:?}")
}
};

// Not returning this error because it is a type error that shouldn't happen unless
// the browser, JS builtin objects, or wasm bindings are misbehaving somehow.
let webgl2_context: web_sys::WebGl2RenderingContext = context_object
.dyn_into()
.expect("canvas context is not a WebGl2RenderingContext");

*self.webgl2_context.lock() = Some(webgl2_context.clone());

Expand Down
48 changes: 39 additions & 9 deletions wgpu/src/backend/web.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1027,22 +1027,52 @@ impl Context {
&self,
canvas: &web_sys::HtmlCanvasElement,
) -> <Self as crate::Context>::SurfaceId {
let context: wasm_bindgen::JsValue = match canvas.get_context("webgpu") {
Ok(Some(ctx)) => ctx.into(),
_ => panic!("expected to get context from canvas"),
};
create_identified(context.into())
self.create_surface_from_context(canvas.get_context("webgpu"))
.unwrap()
}

pub fn instance_create_surface_from_offscreen_canvas(
&self,
canvas: &web_sys::OffscreenCanvas,
) -> <Self as crate::Context>::SurfaceId {
let context: wasm_bindgen::JsValue = match canvas.get_context("webgpu") {
Ok(Some(ctx)) => ctx.into(),
_ => panic!("expected to get context from canvas"),
self.create_surface_from_context(canvas.get_context("webgpu"))
.unwrap()
}

/// Common portion of public `instance_create_surface_from_*` functions.
///
/// Note: Analogous code also exists in the WebGL 2 backend at
/// `wgpu_hal::gles::web::Instance`.
fn create_surface_from_context(
&self,
context_result: Result<Option<js_sys::Object>, wasm_bindgen::JsValue>,
) -> Result<<Self as crate::Context>::SurfaceId, ()> {
let context: js_sys::Object = match context_result {
Ok(Some(context)) => context,
Ok(None) => {
// <https://html.spec.whatwg.org/multipage/canvas.html#dom-canvas-getcontext-dev>
// A getContext() call “returns null if contextId is not supported, or if the
// canvas has already been initialized with another context type”. Additionally,
// “not supported” could include “insufficient GPU resources” or “the GPU process
// previously crashed”. So, we must return it as an `Err` since it could occur
// for circumstances outside the application author's control.
return Err(());
}
Err(js_error) => {
// <https://html.spec.whatwg.org/multipage/canvas.html#dom-canvas-getcontext>
// A thrown exception indicates misuse of the canvas state. Ideally we wouldn't
// panic in this case ... TODO
panic!("canvas.getContext() threw {js_error:?}")
}
};
create_identified(context.into())

// Not returning this error because it is a type error that shouldn't happen unless
// the browser, JS builtin objects, or wasm bindings are misbehaving somehow.
let context: web_sys::GpuCanvasContext = context
.dyn_into()
.expect("canvas context is not a GPUCanvasContext");

Ok(create_identified(context))
}

pub fn queue_copy_external_image_to_texture(
Expand Down