WindowBuilderExtWebSys::with_prevent_default disables scrolling on both mobile and desktop (previously just desktop) (#2216)

* Disable scrolling on web by default but provide method in builder to enable it

* rename enable_web_scroll -> enable_web_page_scroll

* move enable_web_page_scroll into prevent_default option

* final approach

* Mark prevent_default change as breaking

Co-authored-by: Mads Marquart <mads@marquart.dk>

CHANGELOG.md

@@ -18,6 +18,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - On Windows, added `WindowExtWindows::set_undecorated_shadow` and `WindowBuilderExtWindows::with_undecorated_shadow` to draw the drop shadow behind a borderless window.
 - On Windows, fixed default window features (ie snap, animations, shake, etc.) when decorations are disabled.
 - **Breaking:** On macOS, add support for two-finger touchpad magnification and rotation gestures with new events `WindowEvent::TouchpadMagnify` and `WindowEvent::TouchpadRotate`.
+- **Breaking:** On web, the `WindowBuilderExtWebSys::with_prevent_default` setting (enabled by default), now additionally prevents scrolling of the webpage in mobile browsers, previously it only disabled scrolling on desktop.
 - On Wayland, `wayland-csd-adwaita` now uses `ab_glyph` instead of `crossfont` to render the title for decorations.
 - On Wayland, a new `wayland-csd-adwaita-crossfont` feature was added to use `crossfont` instead of `ab_glyph` for decorations.
 - On Wayland, if not otherwise specified use upstream automatic CSD theme selection.

src/platform_impl/web/event_loop/window_target.rs

@@ -63,6 +63,9 @@ impl<T> EventLoopWindowTarget<T> {
         let mut canvas = canvas.borrow_mut();
         canvas.set_attribute("data-raw-handle", &id.0.to_string());
 
+        canvas.on_touch_start(prevent_default);
+        canvas.on_touch_end(prevent_default);
+
         let runner = self.runner.clone();
         canvas.on_blur(move || {
             runner.send_event(Event::WindowEvent {
@@ -153,7 +156,8 @@ impl<T> EventLoopWindowTarget<T> {
         });
 
         let runner = self.runner.clone();
-        canvas.on_cursor_move(move |pointer_id, position, delta, modifiers| {
+        canvas.on_cursor_move(
+            move |pointer_id, position, delta, modifiers| {
                 runner.send_event(Event::WindowEvent {
                     window_id: RootWindowId(id),
                     event: WindowEvent::CursorMoved {
@@ -168,7 +172,9 @@ impl<T> EventLoopWindowTarget<T> {
                         delta: (delta.x, delta.y),
                     },
                 });
-        });
+            },
+            prevent_default,
+        );
 
         let runner = self.runner.clone();
         canvas.on_mouse_press(move |pointer_id, position, button, modifiers| {

src/platform_impl/web/web_sys/canvas.rs

@@ -21,6 +21,8 @@ mod pointer_handler;
 #[allow(dead_code)]
 pub struct Canvas {
     common: Common,
+    on_touch_start: Option<EventListenerHandle<dyn FnMut(Event)>>,
+    on_touch_end: Option<EventListenerHandle<dyn FnMut(Event)>>,
     on_focus: Option<EventListenerHandle<dyn FnMut(FocusEvent)>>,
     on_blur: Option<EventListenerHandle<dyn FnMut(FocusEvent)>>,
     on_keyboard_release: Option<EventListenerHandle<dyn FnMut(KeyboardEvent)>>,
@@ -79,6 +81,8 @@ impl Canvas {
                 raw: canvas,
                 wants_fullscreen: Rc::new(RefCell::new(false)),
             },
+            on_touch_start: None,
+            on_touch_end: None,
             on_blur: None,
             on_focus: None,
             on_keyboard_release: None,
@@ -132,6 +136,22 @@ impl Canvas {
         &self.common.raw
     }
 
+    pub fn on_touch_start(&mut self, prevent_default: bool) {
+        self.on_touch_start = Some(self.common.add_event("touchstart", move |event: Event| {
+            if prevent_default {
+                event.prevent_default();
+            }
+        }));
+    }
+
+    pub fn on_touch_end(&mut self, prevent_default: bool) {
+        self.on_touch_end = Some(self.common.add_event("touchend", move |event: Event| {
+            if prevent_default {
+                event.prevent_default();
+            }
+        }));
+    }
+
     pub fn on_blur<F>(&mut self, mut handler: F)
     where
         F: 'static + FnMut(),
@@ -262,12 +282,14 @@ impl Canvas {
         }
     }
 
-    pub fn on_cursor_move<F>(&mut self, handler: F)
+    pub fn on_cursor_move<F>(&mut self, handler: F, prevent_default: bool)
     where
         F: 'static + FnMut(i32, PhysicalPosition<f64>, PhysicalPosition<f64>, ModifiersState),
     {
         match &mut self.mouse_state {
-            MouseState::HasPointerEvent(h) => h.on_cursor_move(&self.common, handler),
+            MouseState::HasPointerEvent(h) => {
+                h.on_cursor_move(&self.common, handler, prevent_default)
+            }
             MouseState::NoPointerEvent(h) => h.on_cursor_move(&self.common, handler),
         }
     }

src/platform_impl/web/web_sys/canvas/pointer_handler.rs

@@ -88,13 +88,20 @@ impl PointerHandler {
         ));
     }
 
-    pub fn on_cursor_move<F>(&mut self, canvas_common: &super::Common, mut handler: F)
+    pub fn on_cursor_move<F>(
-    where
+        &mut self,
+        canvas_common: &super::Common,
+        mut handler: F,
+        prevent_default: bool,
+    ) where
         F: 'static + FnMut(i32, PhysicalPosition<f64>, PhysicalPosition<f64>, ModifiersState),
     {
         self.on_cursor_move = Some(canvas_common.add_event(
             "pointermove",
             move |event: PointerEvent| {
+                if prevent_default {
+                    event.prevent_default();
+                }
                 handler(
                     event.pointer_id(),
                     event::mouse_position(&event).to_physical(super::super::scale_factor()),