Doc fixes for wgpu_types::Backend::Gl.

Author: jimblandy

README.md

@@ -65,17 +65,17 @@ Contributors are welcome! See [CONTRIBUTING.md][contrib] for more information.
 
 ## Supported Platforms
 
-| API    | Windows      | Linux/Android   | macOS/iOS | Web (wasm)  |
-| ------ | ------------ | --------------- | --------- | ----------- |
-| Vulkan | ✅           | ✅              | 🌋        |             |
-| Metal  |              |                 | ✅        |             |
-| DX12   | ✅           |                 |           |             |
-| OpenGL | 🆗 (GL 3.3+) | 🆗 (GL ES 3.0+) | 📐        | 🆗 (WebGL2) |
-| WebGPU |              |                 |           | ✅          |
+| API    | Windows             | Linux/Android   | macOS/iOS | Web (wasm)  |
+| ------ | ------------------- | --------------- | --------- | ----------- |
+| Vulkan | ✅                  | ✅              | 🌋        |             |
+| Metal  |                     |                 | ✅        |             |
+| DX12   | ✅                  |                 |           |             |
+| OpenGL | 🆗 (GL 3.3+), or 📐 | 🆗 (GL ES 3.0+) | 📐        | 🆗 (WebGL2) |
+| WebGPU |                     |                 |           | ✅          |
 
 ✅ = First Class Support  
 🆗 = Downlevel/Best Effort Support  
-📐 = Requires the [ANGLE](https://github.com/gfx-rs/wgpu/wiki/Running-on-ANGLE) translation layer (GL ES 3.0 only). Use the `angle` feature on macOS/iOS. On Windows, `gles` uses WGL by default; build with `cfg(windows_angle)` to use ANGLE instead.
+📐 = Requires the [ANGLE](https://github.com/gfx-rs/wgpu/wiki/Running-on-ANGLE) translation layer (GL ES 3.0 only). On macOS/iOS, use the `angle` feature. On Windows, `gles` uses WGL by default; build with `cfg(windows_angle)` to use ANGLE instead.
 🌋 = Requires the [MoltenVK](https://vulkan.lunarg.com/sdk/home#mac) translation layer  
 🛠️ = Unsupported, though open to contributions
 

wgpu-types/src/backend.rs

@@ -39,14 +39,29 @@ pub enum Backend {
     /// enables it, in addition to the ordinary requirement of [`Backends::NOOP`] being set.
     /// This ensures that applications not desiring a non-functional backend will not receive it.
     Noop = 0,
+
     /// Vulkan API (Windows, Linux, Android, MacOS via `vulkan-portability`/MoltenVK)
     Vulkan = 1,
+
     /// Metal API (Apple platforms)
     Metal = 2,
+
     /// Direct3D-12 (Windows)
     Dx12 = 3,
-    /// OpenGL 3.3+ (Windows), OpenGL ES 3.0+ (Linux, Android, MacOS via Angle), and WebGL2
+
+    /// OpenGL 3.3+, OpenGL ES 3.0+, WebGL2.
+    ///
+    /// - On Windows, this is normally OpenGL. If you build with
+    ///   `cfg(windows_angle)` to use ANGLE instead, then this is OpenGL ES.
+    ///
+    /// - On Linux, we create a full OpenGL context if possible (Mesa offers
+    ///   it), but if that fails we fall back to OpenGL ES.
+    ///
+    /// - On Android and macOS with ANGLE, we get OpenGL ES.
+    ///
+    /// - When running in a web browser, we get WebGL2.
     Gl = 4,
+
     /// WebGPU in the browser
     BrowserWebGpu = 5,
 }