web: add with_prevent_default, with_focusable

`with_prevent_default` controls whether `event.preventDefault` is called

`with_focusable` controls whether `tabindex` is added

Fixes #1768

CHANGELOG.md

@@ -61,9 +61,10 @@ And please only add new entries to the top of this list, right below the `# Unre
 - Implemented `Eq` for `Fullscreen`, `Theme`, and `UserAttentionType`.
 - **Breaking:** `Window::set_cursor_grab` now accepts `CursorGrabMode` to control grabbing behavior.
 - On Wayland, add support for `Window::set_cursor_position`.
-- Fix on macOS `WindowBuilder::with_disallow_hidpi`, setting true or false by the user no matter the SO default value. 
+- Fix on macOS `WindowBuilder::with_disallow_hidpi`, setting true or false by the user no matter the SO default value.
 - `EventLoopBuilder::build` will now panic when the `EventLoop` is being created more than once.
 - Added `From<u64>` for `WindowId` and `From<WindowId>` for `u64`.
+- On Web, add `with_prevent_default` and `with_focusable` to `WindowBuilderExtWebSys` to control whether events should be propagated.
 
 # 0.26.1 (2022-01-05)
 

src/platform/web.rs

@@ -18,6 +18,17 @@ pub trait WindowExtWebSys {
 
 pub trait WindowBuilderExtWebSys {
     fn with_canvas(self, canvas: Option<HtmlCanvasElement>) -> Self;
+
+    /// Whether `event.preventDefault` should be automatically called to prevent event propagation
+    /// when appropriate.
+    ///
+    /// For example, mouse wheel events are only handled by the canvas by default. This avoids
+    /// the default behavior of scrolling the page.
+    fn with_prevent_default(self, prevent_default: bool) -> Self;
+
+    /// Whether the canvas should be focusable using the tab key. This is necessary to capture
+    /// canvas keyboard events.
+    fn with_focusable(self, focusable: bool) -> Self;
 }
 
 impl WindowBuilderExtWebSys for WindowBuilder {
@@ -26,4 +37,16 @@ impl WindowBuilderExtWebSys for WindowBuilder {
 
         self
     }
+
+    fn with_prevent_default(mut self, prevent_default: bool) -> Self {
+        self.platform_specific.prevent_default = prevent_default;
+
+        self
+    }
+
+    fn with_focusable(mut self, focusable: bool) -> Self {
+        self.platform_specific.focusable = focusable;
+
+        self
+    }
 }

src/platform_impl/web/event_loop/window_target.rs

@@ -50,7 +50,12 @@ impl<T> EventLoopWindowTarget<T> {
         WindowId(self.runner.generate_id())
     }
 
-    pub fn register(&self, canvas: &Rc<RefCell<backend::Canvas>>, id: WindowId) {
+    pub fn register(
+        &self,
+        canvas: &Rc<RefCell<backend::Canvas>>,
+        id: WindowId,
+        prevent_default: bool,
+    ) {
         self.runner.add_canvas(RootWindowId(id), canvas);
         let mut canvas = canvas.borrow_mut();
         canvas.set_attribute("data-raw-handle", &id.0.to_string());
@@ -72,48 +77,57 @@ impl<T> EventLoopWindowTarget<T> {
         });
 
         let runner = self.runner.clone();
-        canvas.on_keyboard_press(move |scancode, virtual_keycode, modifiers| {
-            #[allow(deprecated)]
-            runner.send_event(Event::WindowEvent {
-                window_id: RootWindowId(id),
-                event: WindowEvent::KeyboardInput {
-                    device_id: RootDeviceId(unsafe { DeviceId::dummy() }),
-                    input: KeyboardInput {
-                        scancode,
-                        state: ElementState::Pressed,
-                        virtual_keycode,
-                        modifiers,
+        canvas.on_keyboard_press(
+            move |scancode, virtual_keycode, modifiers| {
+                #[allow(deprecated)]
+                runner.send_event(Event::WindowEvent {
+                    window_id: RootWindowId(id),
+                    event: WindowEvent::KeyboardInput {
+                        device_id: RootDeviceId(unsafe { DeviceId::dummy() }),
+                        input: KeyboardInput {
+                            scancode,
+                            state: ElementState::Pressed,
+                            virtual_keycode,
+                            modifiers,
+                        },
+                        is_synthetic: false,
                     },
-                    is_synthetic: false,
-                },
-            });
-        });
+                });
+            },
+            prevent_default,
+        );
 
         let runner = self.runner.clone();
-        canvas.on_keyboard_release(move |scancode, virtual_keycode, modifiers| {
-            #[allow(deprecated)]
-            runner.send_event(Event::WindowEvent {
-                window_id: RootWindowId(id),
-                event: WindowEvent::KeyboardInput {
-                    device_id: RootDeviceId(unsafe { DeviceId::dummy() }),
-                    input: KeyboardInput {
-                        scancode,
-                        state: ElementState::Released,
-                        virtual_keycode,
-                        modifiers,
+        canvas.on_keyboard_release(
+            move |scancode, virtual_keycode, modifiers| {
+                #[allow(deprecated)]
+                runner.send_event(Event::WindowEvent {
+                    window_id: RootWindowId(id),
+                    event: WindowEvent::KeyboardInput {
+                        device_id: RootDeviceId(unsafe { DeviceId::dummy() }),
+                        input: KeyboardInput {
+                            scancode,
+                            state: ElementState::Released,
+                            virtual_keycode,
+                            modifiers,
+                        },
+                        is_synthetic: false,
                     },
-                    is_synthetic: false,
-                },
-            });
-        });
+                });
+            },
+            prevent_default,
+        );
 
         let runner = self.runner.clone();
-        canvas.on_received_character(move |char_code| {
-            runner.send_event(Event::WindowEvent {
-                window_id: RootWindowId(id),
-                event: WindowEvent::ReceivedCharacter(char_code),
-            });
-        });
+        canvas.on_received_character(
+            move |char_code| {
+                runner.send_event(Event::WindowEvent {
+                    window_id: RootWindowId(id),
+                    event: WindowEvent::ReceivedCharacter(char_code),
+                });
+            },
+            prevent_default,
+        );
 
         let runner = self.runner.clone();
         canvas.on_cursor_leave(move |pointer_id| {
@@ -193,17 +207,20 @@ impl<T> EventLoopWindowTarget<T> {
         });
 
         let runner = self.runner.clone();
-        canvas.on_mouse_wheel(move |pointer_id, delta, modifiers| {
-            runner.send_event(Event::WindowEvent {
-                window_id: RootWindowId(id),
-                event: WindowEvent::MouseWheel {
-                    device_id: RootDeviceId(DeviceId(pointer_id)),
-                    delta,
-                    phase: TouchPhase::Moved,
-                    modifiers,
-                },
-            });
-        });
+        canvas.on_mouse_wheel(
+            move |pointer_id, delta, modifiers| {
+                runner.send_event(Event::WindowEvent {
+                    window_id: RootWindowId(id),
+                    event: WindowEvent::MouseWheel {
+                        device_id: RootDeviceId(DeviceId(pointer_id)),
+                        delta,
+                        phase: TouchPhase::Moved,
+                        modifiers,
+                    },
+                });
+            },
+            prevent_default,
+        );
 
         let runner = self.runner.clone();
         let raw = canvas.raw().clone();

src/platform_impl/web/web_sys/canvas.rs

@@ -62,9 +62,11 @@ impl Canvas {
         // sequential keyboard navigation, but its order is defined by the
         // document's source order.
         // https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/tabindex
-        canvas
-            .set_attribute("tabindex", "0")
-            .map_err(|_| os_error!(OsError("Failed to set a tabindex".to_owned())))?;
+        if attr.focusable {
+            canvas
+                .set_attribute("tabindex", "0")
+                .map_err(|_| os_error!(OsError("Failed to set a tabindex".to_owned())))?;
+        }
 
         let mouse_state = if has_pointer_event() {
             MouseState::HasPointerEvent(pointer_handler::PointerHandler::new())
@@ -148,14 +150,17 @@ impl Canvas {
         }));
     }
 
-    pub fn on_keyboard_release<F>(&mut self, mut handler: F)
+    pub fn on_keyboard_release<F>(&mut self, mut handler: F, prevent_default: bool)
     where
         F: 'static + FnMut(ScanCode, Option<VirtualKeyCode>, ModifiersState),
     {
         self.on_keyboard_release = Some(self.common.add_user_event(
             "keyup",
             move |event: KeyboardEvent| {
-                event.prevent_default();
+                if prevent_default {
+                    event.prevent_default();
+                }
+
                 handler(
                     event::scan_code(&event),
                     event::virtual_key_code(&event),
@@ -165,24 +170,27 @@ impl Canvas {
         ));
     }
 
-    pub fn on_keyboard_press<F>(&mut self, mut handler: F)
+    pub fn on_keyboard_press<F>(&mut self, mut handler: F, prevent_default: bool)
     where
         F: 'static + FnMut(ScanCode, Option<VirtualKeyCode>, ModifiersState),
     {
         self.on_keyboard_press = Some(self.common.add_user_event(
             "keydown",
             move |event: KeyboardEvent| {
                 // event.prevent_default() would suppress subsequent on_received_character() calls. That
-                // supression is correct for key sequences like Tab/Shift-Tab, Ctrl+R, PgUp/Down to
+                // suppression is correct for key sequences like Tab/Shift-Tab, Ctrl+R, PgUp/Down to
                 // scroll, etc. We should not do it for key sequences that result in meaningful character
                 // input though.
-                let event_key = &event.key();
-                let is_key_string = event_key.len() == 1 || !event_key.is_ascii();
-                let is_shortcut_modifiers =
-                    (event.ctrl_key() || event.alt_key()) && !event.get_modifier_state("AltGr");
-                if !is_key_string || is_shortcut_modifiers {
-                    event.prevent_default();
+                if prevent_default {
+                    let event_key = &event.key();
+                    let is_key_string = event_key.len() == 1 || !event_key.is_ascii();
+                    let is_shortcut_modifiers =
+                        (event.ctrl_key() || event.alt_key()) && !event.get_modifier_state("AltGr");
+                    if !is_key_string || is_shortcut_modifiers {
+                        event.prevent_default();
+                    }
                 }
+
                 handler(
                     event::scan_code(&event),
                     event::virtual_key_code(&event),
@@ -192,7 +200,7 @@ impl Canvas {
         ));
     }
 
-    pub fn on_received_character<F>(&mut self, mut handler: F)
+    pub fn on_received_character<F>(&mut self, mut handler: F, prevent_default: bool)
     where
         F: 'static + FnMut(char),
     {
@@ -204,8 +212,11 @@ impl Canvas {
         self.on_received_character = Some(self.common.add_user_event(
             "keypress",
             move |event: KeyboardEvent| {
-                // Supress further handling to stop keys like the space key from scrolling the page.
-                event.prevent_default();
+                // Suppress further handling to stop keys like the space key from scrolling the page.
+                if prevent_default {
+                    event.prevent_default();
+                }
+
                 handler(event::codepoint(&event));
             },
         ));
@@ -261,12 +272,15 @@ impl Canvas {
         }
     }
 
-    pub fn on_mouse_wheel<F>(&mut self, mut handler: F)
+    pub fn on_mouse_wheel<F>(&mut self, mut handler: F, prevent_default: bool)
     where
         F: 'static + FnMut(i32, MouseScrollDelta, ModifiersState),
     {
         self.on_mouse_wheel = Some(self.common.add_event("wheel", move |event: WheelEvent| {
-            event.prevent_default();
+            if prevent_default {
+                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

@@ -35,12 +35,14 @@ impl Window {
 
         let id = target.generate_id();
 
+        let prevent_default = platform_attr.prevent_default;
+
         let canvas = backend::Canvas::create(platform_attr)?;
         let canvas = Rc::new(RefCell::new(canvas));
 
         let register_redraw_request = Box::new(move || runner.request_redraw(RootWI(id)));
 
-        target.register(&canvas, id);
+        target.register(&canvas, id, prevent_default);
 
         let runner = target.runner.clone();
         let resize_notify_fn = Box::new(move |new_size| {
@@ -392,7 +394,19 @@ impl From<u64> for WindowId {
     }
 }
 
-#[derive(Default, Clone)]
+#[derive(Clone)]
 pub struct PlatformSpecificWindowBuilderAttributes {
     pub(crate) canvas: Option<backend::RawCanvasType>,
+    pub(crate) prevent_default: bool,
+    pub(crate) focusable: bool,
+}
+
+impl Default for PlatformSpecificWindowBuilderAttributes {
+    fn default() -> Self {
+        Self {
+            canvas: None,
+            prevent_default: true,
+            focusable: true,
+        }
+    }
 }