Disable scrolling on web by default but provide method in builder to …

…enable it

CHANGELOG.md

@@ -12,6 +12,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - Added `Window::is_resizable`.
 - Added `Window::is_decorated`.
 - On X11, fix for repeated event loop iteration when `ControlFlow` was `Wait`
+- On web, by default, when the canvas is focused, scrolling of the webpage is disabled. It can however be enabled via the `WindowBuilderExtWebSys::enable_web_scroll` method.
 - On Wayland, report unaccelerated mouse deltas in `DeviceEvent::MouseMotion`.
 - **Breaking:** Bump `ndk` version to 0.6, ndk-sys to `v0.3`, `ndk-glue` to `0.6`.
 - Remove no longer needed `WINIT_LINK_COLORSYNC` environment variable.

src/platform/web.rs

@@ -17,10 +17,25 @@ pub trait WindowExtWebSys {
 }
 
 pub trait WindowBuilderExtWebSys {
+    /// Enable scrolling of the web page the canvas is in when the canvas is focused.
+    ///
+    /// Scrolling is disabled by default because the scroll input on many mobile devices
+    /// is the same as click and dragging which is a very common input method for many applications.
+    ///
+    /// So only call this method if you know that you will never need to handle mouse wheel inputs
+    /// or click and dragging.
+    fn enable_web_scroll(self) -> Self;
+
     fn with_canvas(self, canvas: Option<HtmlCanvasElement>) -> Self;
 }
 
 impl WindowBuilderExtWebSys for WindowBuilder {
+    fn enable_web_scroll(mut self) -> Self {
+        self.platform_specific.enable_web_scroll = true;
+
+        self
+    }
+
     fn with_canvas(mut self, canvas: Option<HtmlCanvasElement>) -> Self {
         self.platform_specific.canvas = canvas;
 

src/platform_impl/web/web_sys/canvas.rs

@@ -30,6 +30,7 @@ pub struct Canvas {
     on_fullscreen_change: Option<EventListenerHandle<dyn FnMut(Event)>>,
     on_dark_mode: Option<MediaQueryListHandle>,
     mouse_state: MouseState,
+    disable_web_scroll: Option<[EventListenerHandle<dyn FnMut(Event)>; 5]>,
 }
 
 struct Common {
@@ -72,11 +73,34 @@ impl Canvas {
             MouseState::NoPointerEvent(mouse_handler::MouseHandler::new())
         };
 
+        let common = Common {
+            raw: canvas,
+            wants_fullscreen: Rc::new(RefCell::new(false)),
+        };
+
+        let disable_web_scroll = if !attr.enable_web_scroll {
+            Some([
+                common.add_event("pointermove", move |event: Event| {
+                    event.prevent_default();
+                }),
+                common.add_event("pointermove", move |event: Event| {
+                    event.prevent_default();
+                }),
+                common.add_event("touchstart", move |event: Event| {
+                    event.prevent_default();
+                }),
+                common.add_event("touchend", move |event: Event| {
+                    event.prevent_default();
+                }),
+                common.add_event("wheel", move |event: Event| {
+                    event.prevent_default();
+                }),
+            ])
+        } else {
+            None
+        };
+
         Ok(Canvas {
-            common: Common {
-                raw: canvas,
-                wants_fullscreen: Rc::new(RefCell::new(false)),
-            },
             on_blur: None,
             on_focus: None,
             on_keyboard_release: None,
@@ -86,6 +110,8 @@ impl Canvas {
             on_fullscreen_change: None,
             on_dark_mode: None,
             mouse_state,
+            disable_web_scroll,
+            common,
         })
     }
 
@@ -266,7 +292,6 @@ impl Canvas {
         F: 'static + FnMut(i32, MouseScrollDelta, ModifiersState),
     {
         self.on_mouse_wheel = Some(self.common.add_event("wheel", move |event: WheelEvent| {
-            event.prevent_default();
             if let Some(delta) = event::mouse_scroll_delta(&event) {
                 handler(0, delta, event::mouse_modifiers(&event));
             }

src/platform_impl/web/window.rs

@@ -365,4 +365,5 @@ impl Id {
 #[derive(Default, Clone)]
 pub struct PlatformSpecificBuilderAttributes {
     pub(crate) canvas: Option<backend::RawCanvasType>,
+    pub(crate) enable_web_scroll: bool,
 }