Make wgpu the default renderer for eframe and egui.rs (#7615)

* Closes https://github.com/emilk/egui/issues/5889

See the above issue for motivation.

To use glow instead, disable the default features of `eframe` and opt-in
to `glow`.

This also changes egui.rs to use wgpu, which means WebGPU when
available, and WebGL otherwise

Cargo.toml

@@ -232,6 +232,7 @@ iter_on_single_items = "warn"
 iter_over_hash_type = "warn"
 iter_without_into_iter = "warn"
 large_digit_groups = "warn"
+large_futures = "warn"
 large_include_file = "warn"
 large_stack_arrays = "warn"
 large_stack_frames = "warn"
@@ -329,6 +330,7 @@ unnecessary_semicolon = "warn"
 unnecessary_struct_initialization = "warn"
 unnecessary_wraps = "warn"
 unnested_or_patterns = "warn"
+unused_async = "warn"
 unused_peekable = "warn"
 unused_rounding = "warn"
 unused_self = "warn"

crates/eframe/Cargo.toml

@@ -28,9 +28,9 @@ workspace = true
 default = [
   "accesskit",
   "default_fonts",
-  "glow",
   "wayland", # Required for Linux support (including CI!)
   "web_screen_reader",
+  "wgpu",
   "winit/default",
   "x11",
 ]
@@ -52,7 +52,11 @@ android-native-activity = ["egui-winit/android-native-activity"]
 ## If you plan on specifying your own fonts you may disable this feature.
 default_fonts = ["egui/default_fonts"]
 
-## Use [`glow`](https://github.com/grovesNL/glow) for painting, via [`egui_glow`](https://github.com/emilk/egui/tree/main/crates/egui_glow).
+## Enable [`glow`](https://github.com/grovesNL/glow) for painting, via [`egui_glow`](https://github.com/emilk/egui/tree/main/crates/egui_glow).
+##
+## There is generally no need to enable both the `wgpu` and `glow` features,
+## but if you do you can pick the renderer to use with [`NativeOptions::renderer`]
+## and `WebOptions::renderer`.
 glow = ["dep:egui_glow", "dep:glow", "dep:glutin-winit", "dep:glutin"]
 
 ## Enable saving app state to disk.
@@ -74,9 +78,15 @@ wayland = [
 ## For other platforms, use the `accesskit` feature instead.
 web_screen_reader = ["web-sys/SpeechSynthesis", "web-sys/SpeechSynthesisUtterance"]
 
-## Use [`wgpu`](https://docs.rs/wgpu) for painting (via [`egui-wgpu`](https://github.com/emilk/egui/tree/main/crates/egui-wgpu)).
+## Enable [`wgpu`](https://docs.rs/wgpu) for painting (via [`egui-wgpu`](https://github.com/emilk/egui/tree/main/crates/egui-wgpu)).
 ##
-## This overrides the `glow` feature.
+## There is generally no need to enable both the `wgpu` and `glow` features,
+## but if you do you can pick the renderer to use with [`NativeOptions::renderer`]
+## and `WebOptions::renderer`.
+##
+## Switching from `wgpu (the default)` to `glow` can significantly reduce your binary size
+## (including the .wasm of a web app).
+## See <https://github.com/emilk/egui/issues/5889> for more details.
 ##
 ## By default, eframe will prefer WebGPU over WebGL, but
 ## you can configure this at run-time with [`NativeOptions::wgpu_options`].

crates/eframe/src/epi.rs

@@ -471,6 +471,10 @@ impl Default for NativeOptions {
 /// Options when using `eframe` in a web page.
 #[cfg(target_arch = "wasm32")]
 pub struct WebOptions {
+    /// What rendering backend to use.
+    #[cfg(any(feature = "glow", feature = "wgpu_no_default_features"))]
+    pub renderer: Renderer,
+
     /// Sets the number of bits in the depth buffer.
     ///
     /// `egui` doesn't need the depth buffer, so the default value is 0.
@@ -519,6 +523,9 @@ pub struct WebOptions {
 impl Default for WebOptions {
     fn default() -> Self {
         Self {
+            #[cfg(any(feature = "glow", feature = "wgpu_no_default_features"))]
+            renderer: Renderer::default(),
+
             depth_buffer: 0,
 
             #[cfg(feature = "glow")]
@@ -592,8 +599,8 @@ impl Default for Renderer {
         #[cfg(feature = "wgpu_no_default_features")]
         return Self::Wgpu;
 
-        // By default, only the `glow` feature is enabled, so if the user added `wgpu` to the feature list
-        // they probably wanted to use wgpu:
+        // It's weird that the user has enabled both glow and wgpu,
+        // but let's pick the better of the two (wgpu):
         #[cfg(feature = "glow")]
         #[cfg(feature = "wgpu_no_default_features")]
         return Self::Wgpu;

crates/eframe/src/web/app_runner.rs

@@ -1,15 +1,15 @@
 use egui::{TexturesDelta, UserData, ViewportCommand};
 
-use crate::{App, epi};
+use crate::{App, epi, web::web_painter::WebPainter};
 
-use super::{NeedRepaint, now_sec, text_agent::TextAgent, web_painter::WebPainter as _};
+use super::{NeedRepaint, now_sec, text_agent::TextAgent};
 
 pub struct AppRunner {
     #[allow(dead_code, clippy::allow_attributes)]
     pub(crate) web_options: crate::WebOptions,
     pub(crate) frame: epi::Frame,
     egui_ctx: egui::Context,
-    painter: super::ActiveWebPainter,
+    painter: Box<dyn WebPainter>,
     pub(crate) input: super::WebInput,
     app: Box<dyn epi::App>,
     pub(crate) needs_repaint: std::sync::Arc<NeedRepaint>,
@@ -34,6 +34,10 @@ impl Drop for AppRunner {
 impl AppRunner {
     /// # Errors
     /// Failure to initialize WebGL renderer, or failure to create app.
+    #[cfg_attr(
+        not(feature = "wgpu_no_default_features"),
+        expect(clippy::unused_async)
+    )]
     pub async fn new(
         canvas: web_sys::HtmlCanvasElement,
         web_options: crate::WebOptions,
@@ -41,7 +45,41 @@ impl AppRunner {
         text_agent: TextAgent,
     ) -> Result<Self, String> {
         let egui_ctx = egui::Context::default();
-        let painter = super::ActiveWebPainter::new(egui_ctx.clone(), canvas, &web_options).await?;
+
+        #[allow(clippy::allow_attributes, unused_assignments)]
+        #[cfg(feature = "glow")]
+        let mut gl = None;
+
+        #[allow(clippy::allow_attributes, unused_assignments)]
+        #[cfg(feature = "wgpu_no_default_features")]
+        let mut wgpu_render_state = None;
+
+        let painter = match web_options.renderer {
+            #[cfg(feature = "glow")]
+            epi::Renderer::Glow => {
+                log::debug!("Using the glow renderer");
+                let painter = super::web_painter_glow::WebPainterGlow::new(
+                    egui_ctx.clone(),
+                    canvas,
+                    &web_options,
+                )?;
+                gl = Some(painter.gl().clone());
+                Box::new(painter) as Box<dyn WebPainter>
+            }
+
+            #[cfg(feature = "wgpu_no_default_features")]
+            epi::Renderer::Wgpu => {
+                log::debug!("Using the wgpu renderer");
+                let painter = super::web_painter_wgpu::WebPainterWgpu::new(
+                    egui_ctx.clone(),
+                    canvas,
+                    &web_options,
+                )
+                .await?;
+                wgpu_render_state = painter.render_state();
+                Box::new(painter) as Box<dyn WebPainter>
+            }
+        };
 
         let info = epi::IntegrationInfo {
             web_info: epi::WebInfo {
@@ -79,15 +117,13 @@ impl AppRunner {
             storage: Some(&storage),
 
             #[cfg(feature = "glow")]
-            gl: Some(painter.gl().clone()),
+            gl: gl.clone(),
 
             #[cfg(feature = "glow")]
             get_proc_address: None,
 
-            #[cfg(all(feature = "wgpu_no_default_features", not(feature = "glow")))]
-            wgpu_render_state: painter.render_state(),
-            #[cfg(all(feature = "wgpu_no_default_features", feature = "glow"))]
-            wgpu_render_state: None,
+            #[cfg(feature = "wgpu_no_default_features")]
+            wgpu_render_state: wgpu_render_state.clone(),
         };
         let app = app_creator(&cc).map_err(|err| err.to_string())?;
 
@@ -96,12 +132,10 @@ impl AppRunner {
             storage: Some(Box::new(storage)),
 
             #[cfg(feature = "glow")]
-            gl: Some(painter.gl().clone()),
+            gl,
 
-            #[cfg(all(feature = "wgpu_no_default_features", not(feature = "glow")))]
-            wgpu_render_state: painter.render_state(),
-            #[cfg(all(feature = "wgpu_no_default_features", feature = "glow"))]
-            wgpu_render_state: None,
+            #[cfg(feature = "wgpu_no_default_features")]
+            wgpu_render_state,
         };
 
         let needs_repaint: std::sync::Arc<NeedRepaint> =

crates/eframe/src/web/mod.rs

@@ -30,13 +30,9 @@ mod web_painter;
 
 #[cfg(feature = "glow")]
 mod web_painter_glow;
-#[cfg(feature = "glow")]
-pub(crate) type ActiveWebPainter = web_painter_glow::WebPainterGlow;
 
 #[cfg(feature = "wgpu_no_default_features")]
 mod web_painter_wgpu;
-#[cfg(all(feature = "wgpu_no_default_features", not(feature = "glow")))]
-pub(crate) type ActiveWebPainter = web_painter_wgpu::WebPainterWgpu;
 
 pub use backend::*;
 

crates/eframe/src/web/web_painter_glow.rs

@@ -20,7 +20,7 @@ impl WebPainterGlow {
         self.painter.gl()
     }
 
-    pub async fn new(
+    pub fn new(
         _ctx: egui::Context,
         canvas: HtmlCanvasElement,
         options: &WebOptions,

crates/eframe/src/web/web_painter_wgpu.rs

@@ -1,13 +1,15 @@
 use std::sync::Arc;
 
-use super::web_painter::WebPainter;
-use crate::WebOptions;
 use egui::{Event, UserData, ViewportId};
-use egui_wgpu::capture::{CaptureReceiver, CaptureSender, CaptureState, capture_channel};
-use egui_wgpu::{RenderState, SurfaceErrorAction};
+use egui_wgpu::{
+    RenderState, SurfaceErrorAction,
+    capture::{CaptureReceiver, CaptureSender, CaptureState, capture_channel},
+};
 use wasm_bindgen::JsValue;
 use web_sys::HtmlCanvasElement;
 
+use super::web_painter::WebPainter;
+
 pub(crate) struct WebPainterWgpu {
     canvas: HtmlCanvasElement,
     surface: wgpu::Surface<'static>,
@@ -23,7 +25,6 @@ pub(crate) struct WebPainterWgpu {
 }
 
 impl WebPainterWgpu {
-    #[expect(unused)] // only used if `wgpu` is the only active feature.
     pub fn render_state(&self) -> Option<RenderState> {
         self.render_state.clone()
     }
@@ -55,11 +56,10 @@ impl WebPainterWgpu {
         })
     }
 
-    #[expect(unused)] // only used if `wgpu` is the only active feature.
     pub async fn new(
         ctx: egui::Context,
         canvas: web_sys::HtmlCanvasElement,
-        options: &WebOptions,
+        options: &crate::WebOptions,
     ) -> Result<Self, String> {
         log::debug!("Creating wgpu painter");
 

crates/egui_demo_app/Cargo.toml

@@ -23,7 +23,7 @@ crate-type = ["cdylib", "rlib"]
 
 
 [features]
-default = ["glow", "persistence"]
+default = ["wgpu", "persistence"]
 
 # image_viewer adds about 0.9 MB of WASM
 web_app = ["http", "persistence"]

scripts/build_demo_web.sh

@@ -13,13 +13,13 @@ OPEN=false
 OPTIMIZE=false
 BUILD=debug
 BUILD_FLAGS=""
-WGPU=false
+GLOW=false
 WASM_OPT_FLAGS="-O2 --fast-math"
 
 while test $# -gt 0; do
   case "$1" in
     -h|--help)
-      echo "build_demo_web.sh [--release] [--wgpu] [--open]"
+      echo "build_demo_web.sh [--release] [--glow] [--open]"
       echo ""
       echo "  -g:        Keep debug symbols even with --release."
       echo "             These are useful profiling and size trimming."
@@ -29,9 +29,7 @@ while test $# -gt 0; do
       echo "  --release: Build with --release, and then run wasm-opt."
       echo "             NOTE: --release also removes debug symbols, unless you also use -g."
       echo ""
-      echo "  --wgpu:    Build a binary using wgpu instead of glow/webgl."
-      echo "             The resulting binary will automatically use WebGPU if available and"
-      echo "             fall back to a WebGL emulation layer otherwise."
+      echo "  --glow:    Build a binary using glow instead of wgpu."
       exit 0
       ;;
 
@@ -52,9 +50,9 @@ while test $# -gt 0; do
       BUILD_FLAGS="--release"
       ;;
 
-    --wgpu)
+    --glow)
       shift
-      WGPU=true
+      GLOW=true
       ;;
 
     *)
@@ -66,10 +64,10 @@ done
 
 OUT_FILE_NAME="egui_demo_app"
 
-if [[ "${WGPU}" == true ]]; then
-  FEATURES="${FEATURES},wgpu"
-else
+if [[ "${GLOW}" == true ]]; then
   FEATURES="${FEATURES},glow"
+else
+  FEATURES="${FEATURES},wgpu"
 fi
 
 FINAL_WASM_PATH=web_demo/${OUT_FILE_NAME}_bg.wasm