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Emscripten wgpu-hal example is broken #3245

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jimblandy opened this issue Nov 29, 2022 · 10 comments
Closed

Emscripten wgpu-hal example is broken #3245

jimblandy opened this issue Nov 29, 2022 · 10 comments
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api: gles Issues with GLES or WebGL type: bug Something isn't working

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@jimblandy
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When I build wgpu-hal/examples/raw-gles.rs according to the instructions in #2422, I get the following error in the page's console:

This page is in Quirks Mode. Page layout may be impacted. For Standards Mode use “<!DOCTYPE html>”.
[raw-gles.em.html](http://localhost:8000/raw-gles.em.html)
GEThttp://localhost:8000/favicon.ico
[HTTP/1.0 404 File not found 1ms]

Initializing external GL context [raw-gles.js:1799:16](http://localhost:8000/raw-gles.js)
Hooking up to wgpu-hal [raw-gles.js:1799:16](http://localhost:8000/raw-gles.js)
thread 'main' panicked at 'Get parameter string 0x9245 failed. Maybe your GL context version is too outdated.', /home/jimb/.cargo/git/checkouts/glow-0323f9242b6190b5/c8a011f/src/native.rs:1181:13 [raw-gles.js:1811:16](http://localhost:8000/raw-gles.js)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace [raw-gles.js:1811:16](http://localhost:8000/raw-gles.js)
WebGL warning: getParameter: Bad `pname`: 0x9245

I'm building and serving the page as follows:

$  cargo clean
$  EMCC_CFLAGS="-g -s ERROR_ON_UNDEFINED_SYMBOLS=0 --no-entry -s FULL_ES3=1" cargo build --example raw-gles --target wasm32-unknown-emscripten --features gles,emscripten,webgl
$  cp wgpu-hal/examples/raw-gles.em.html target/wasm32-unknown-emscripten/debug/examples/
$  cd target/wasm32-unknown-emscripten/debug/examples/
$  python -m http.server
@jimblandy jimblandy added type: bug Something isn't working api: gles Issues with GLES or WebGL labels Nov 29, 2022
@jimblandy
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FWIW, the GLenum 0x9245 is UNMASKED_VENDOR_WEBGL in the WEBGL_debug_renderer_info extension.

@jimblandy
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The bug seems to be that wgpu_hal::gles::Adapter::expose calls gl.get_parameter_string(GL_UNMASKED_VENDOR_WEBGL) without actually enabling the WEBGL_debug_renderer_info extension. It merely checks that the extension is present.

@jimblandy
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We should update the wiki when this is fixed.

@jimblandy
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glow has code to enable that extension here, but only for non-Emscripten wasm32.

@jimblandy
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jimblandy commented Nov 30, 2022 •
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It seems to me that it's Emscripten's job to enable these extensions, if it wants to pretend to be GLES (which does not require extensions to be enabled) while actually running on WebGL (which does). I'm not sure we have any next moves here.

@jimblandy jimblandy mentioned this issue Nov 30, 2022
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@coderedart coderedart mentioned this issue Feb 11, 2023
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@coderedart
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Is there any significance to UNMASKED_VENDOR_WEBGL? since it seems to just be used for info, wgpu can hardcode a fixed string, as a temporary workaround.

Also, is it possible to use https://github.com/emscripten-core/emscripten/blob/main/system/include/emscripten/html5_webgl.h#L61

emscripten_webgl_enable_extension(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context, const char *extension);

to manually enable this extension inside wgpu before calling getString?

@coderedart
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If i add the following lines after making context current ->

unsafe { 
        let ctx = emscripten_webgl_get_current_context();
        emscripten_webgl_enable_extension(ctx, "WEBGL_debug_renderer_info\0".as_ptr() as _);
    }

the example works with no issues.

@coderedart
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So, this error arises because emscripten explicitly avoids enabling this extension at https://github.com/emscripten-core/emscripten/blob/main/src/library_webgl.js#L1135

IDK the main reason they do this, but I am guessing because this extension might not be available in firefox.
https://developer.mozilla.org/en-US/docs/Web/API/WEBGL_debug_renderer_info states

Note: Depending on the privacy settings of the browser, this extension might only be available to privileged contexts or not work at all. In Firefox, if privacy.resistFingerprinting is set to true, this extensions is disabled.

The bug reports in firefox primarily talk about how UNMASKED_RENDERER provides more info about user's hardware than necessary and easily exploited for fingerprinting. https://bugzilla.mozilla.org/show_bug.cgi?id=1722782#c10

@coderedart coderedart mentioned this issue Feb 21, 2023
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@teoxoy
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teoxoy commented Feb 22, 2023

Did #3519 fix this issue?

@cwfitzgerald
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Yes

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@jimblandy @cwfitzgerald @coderedart @teoxoy