enable debug extension on emscripten (#3519)

* enable debug extension on emscripten

* update changelog

* extract emscripten stuff into a separate module

* use unmasked queries on w-u-u, and only enable extension on emscripten

* fix docs

CHANGELOG.md

@@ -102,6 +102,7 @@ By @teoxoy in [#3436](https://github.com/gfx-rs/wgpu/pull/3436)
 #### GLES
 
 - [gles] fix: Set FORCE_POINT_SIZE if it is vertex shader with mesh consist of point list. By @REASY in [3440](https://github.com/gfx-rs/wgpu/pull/3440)
+- [gles] fix: enable `WEBGL_debug_renderer_info` before querying unmasked vendor/renderer to avoid crashing on emscripten in [#3519](https://github.com/gfx-rs/wgpu/pull/3519)
 
 #### General
 

wgpu-hal/src/gles/adapter.rs

@@ -186,10 +186,21 @@ impl super::Adapter {
         let extensions = gl.supported_extensions();
 
         let (vendor_const, renderer_const) = if extensions.contains("WEBGL_debug_renderer_info") {
+            // emscripten doesn't enable "WEBGL_debug_renderer_info" extension by default. so, we do it manually.
+            // See https://github.com/gfx-rs/wgpu/issues/3245 for context
+            #[cfg(target_os = "emscripten")]
+            if unsafe { super::emscripten::enable_extension("WEBGL_debug_renderer_info\0") } {
+                (GL_UNMASKED_VENDOR_WEBGL, GL_UNMASKED_RENDERER_WEBGL)
+            } else {
+                (glow::VENDOR, glow::RENDERER)
+            }
+            // glow already enables WEBGL_debug_renderer_info on wasm32-unknown-unknown target by default.
+            #[cfg(not(target_os = "emscripten"))]
             (GL_UNMASKED_VENDOR_WEBGL, GL_UNMASKED_RENDERER_WEBGL)
         } else {
             (glow::VENDOR, glow::RENDERER)
         };
+
         let (vendor, renderer) = {
             let vendor = unsafe { gl.get_parameter_string(vendor_const) };
             let renderer = unsafe { gl.get_parameter_string(renderer_const) };

wgpu-hal/src/gles/emscripten.rs

@@ -0,0 +1,26 @@
+extern "C" {
+    /// returns 1 if success. 0 if failure. extension name must be null terminated
+    fn emscripten_webgl_enable_extension(
+        context: std::ffi::c_int,
+        extension: *const std::ffi::c_char,
+    ) -> std::ffi::c_int;
+    fn emscripten_webgl_get_current_context() -> std::ffi::c_int;
+}
+/// Webgl requires extensions to be enabled before using them.
+/// This function can be used to enable webgl extension on emscripten target.
+///
+/// returns true on success
+///
+/// # Safety:
+///
+/// - opengl context MUST BE current
+/// - extension_name_null_terminated argument must be a valid string with null terminator.
+/// - extension must be present. check `glow_context.supported_extensions()`
+pub unsafe fn enable_extension(extension_name_null_terminated: &str) -> bool {
+    unsafe {
+        emscripten_webgl_enable_extension(
+            emscripten_webgl_get_current_context(),
+            extension_name_null_terminated.as_ptr() as _,
+        ) == 1
+    }
+}

wgpu-hal/src/gles/mod.rs

@@ -59,6 +59,8 @@ To address this, we invalidate the vertex buffers based on:
 ///cbindgen:ignore
 #[cfg(any(not(target_arch = "wasm32"), target_os = "emscripten"))]
 mod egl;
+#[cfg(target_os = "emscripten")]
+mod emscripten;
 #[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
 mod web;