Demote OpenGL to optional feature (#20793)

# Objective

In practice, we don't test OpenGL support and it's been reported broken
for several releases.

## Solution

Make the `gles` feature for `wgpu` optional, reflecting our level of
support.

Author: tychedelia

crates/bevy_render/Cargo.toml

@@ -40,6 +40,7 @@ tracing-tracy = ["dep:tracy-client"]
 ci_limits = []
 webgl = ["wgpu/webgl"]
 webgpu = ["wgpu/webgpu"]
+gles = ["wgpu/gles"]
 detailed_trace = []
 ## Adds serialization support through `serde`.
 serialize = ["bevy_mesh/serialize"]
@@ -86,7 +87,6 @@ wgpu = { version = "26", default-features = false, features = [
   "dx12",
   "metal",
   "vulkan",
-  "gles",
   "naga-ir",
   "fragile-send-sync-non-atomic-wasm",
 ] }

crates/bevy_render/src/settings.rs

@@ -27,8 +27,8 @@ pub enum WgpuSettingsPriority {
 /// [`Backends::VULKAN`](Backends::VULKAN) are enabled by default for non-web and the best choice
 /// is automatically selected. Web using the `webgl` feature uses [`Backends::GL`](Backends::GL).
 /// NOTE: If you want to use [`Backends::GL`](Backends::GL) in a native app on `Windows` and/or `macOS`, you must
-/// use [`ANGLE`](https://github.com/gfx-rs/wgpu#angle). This is because wgpu requires EGL to
-/// create a GL context without a window and only ANGLE supports that.
+/// use [`ANGLE`](https://github.com/gfx-rs/wgpu#angle) and enable the `gles` feature. This is
+/// because wgpu requires EGL to create a GL context without a window and only ANGLE supports that.
 #[derive(Clone)]
 pub struct WgpuSettings {
     pub device_label: Option<Cow<'static, str>>,

crates/bevy_render/src/view/window/mod.rs

@@ -205,10 +205,10 @@ impl WindowSurfaces {
 ///   `DirectX 11` is not supported by wgpu 0.12 and so if your GPU/drivers do not support Vulkan,
 ///   it may be that a software renderer called "Microsoft Basic Render Driver" using `DirectX 12`
 ///   will be chosen and performance will be very poor. This is visible in a log message that is
-///   output during renderer initialization. Future versions of wgpu will support `DirectX 11`, but
-///   another alternative is to try to use [`ANGLE`](https://github.com/gfx-rs/wgpu#angle) and
-///   [`Backends::GL`](crate::settings::Backends::GL) if your GPU/drivers support `OpenGL 4.3` / `OpenGL ES 3.0` or
-///   later.
+///   output during renderer initialization.
+///   Another alternative is to try to use [`ANGLE`](https://github.com/gfx-rs/wgpu#angle) and
+///   [`Backends::GL`](crate::settings::Backends::GL) with the `gles` feature enabled if your
+///   GPU/drivers support `OpenGL 4.3` / `OpenGL ES 3.0` or later.
 pub fn prepare_windows(
     mut windows: ResMut<ExtractedWindows>,
     mut window_surfaces: ResMut<WindowSurfaces>,

release-content/migration-guides/gles_optional.md

@@ -0,0 +1,9 @@
+---
+title: "OpenGL ES `wgpu` backend is no longer supported by default"
+pull_requests: [ 20793 ]
+---
+
+The `gles` backend for `wgpu` is no longer included as a default feature of `bevy_render`. OpenGL support is still
+available, but must be explicitly enabled by adding the `bevy_render/gles` feature to your app. This change reflects the
+fact that OpenGL support is not tested and that some features may not work as expected or at all. We welcome
+contributions to improve OpenGL support in the future.