Add raw mouse wheel event

crates/eframe/src/web/events.rs

@@ -402,20 +402,33 @@ pub fn install_canvas_events(runner_container: &mut AppRunnerContainer) -> Resul
         &canvas,
         "wheel",
         |event: web_sys::WheelEvent, mut runner_lock| {
-            let scroll_multiplier = match event.delta_mode() {
-                web_sys::WheelEvent::DOM_DELTA_PAGE => {
-                    canvas_size_in_points(runner_lock.canvas_id()).y
-                }
-                web_sys::WheelEvent::DOM_DELTA_LINE => {
+            let unit = match event.delta_mode() {
+                web_sys::WheelEvent::DOM_DELTA_PIXEL => egui::MouseWheelUnit::Point,
+                web_sys::WheelEvent::DOM_DELTA_LINE => egui::MouseWheelUnit::Line,
+                web_sys::WheelEvent::DOM_DELTA_PAGE => egui::MouseWheelUnit::Page,
+                _ => return,
+            };
+            // delta sign is flipped to match native (winit) convention.
+            let delta = -egui::vec2(event.delta_x() as f32, event.delta_y() as f32);
+            let modifiers = runner_lock.input.raw.modifiers;
+
+            runner_lock.input.raw.events.push(egui::Event::MouseWheel {
+                unit,
+                delta,
+                modifiers,
+            });
+
+            let scroll_multiplier = match unit {
+                egui::MouseWheelUnit::Page => canvas_size_in_points(runner_lock.canvas_id()).y,
+                egui::MouseWheelUnit::Line => {
                     #[allow(clippy::let_and_return)]
                     let points_per_scroll_line = 8.0; // Note that this is intentionally different from what we use in winit.
                     points_per_scroll_line
                 }
-                _ => 1.0, // DOM_DELTA_PIXEL
+                egui::MouseWheelUnit::Point => 1.0,
             };
 
-            let mut delta =
-                -scroll_multiplier * egui::vec2(event.delta_x() as f32, event.delta_y() as f32);
+            let mut delta = scroll_multiplier * delta;
 
             // Report a zoom event in case CTRL (on Windows or Linux) or CMD (on Mac) is pressed.
             // This if-statement is equivalent to how `Modifiers.command` is determined in

crates/egui-winit/src/lib.rs

@@ -549,6 +549,26 @@ impl State {
     }
 
     fn on_mouse_wheel(&mut self, delta: winit::event::MouseScrollDelta) {
+        {
+            let (unit, delta) = match delta {
+                winit::event::MouseScrollDelta::LineDelta(x, y) => {
+                    (egui::MouseWheelUnit::Line, egui::vec2(x, y))
+                }
+                winit::event::MouseScrollDelta::PixelDelta(winit::dpi::PhysicalPosition {
+                    x,
+                    y,
+                }) => (
+                    egui::MouseWheelUnit::Point,
+                    egui::vec2(x as f32, y as f32) / self.pixels_per_point(),
+                ),
+            };
+            let modifiers = self.egui_input.modifiers;
+            self.egui_input.events.push(egui::Event::MouseWheel {
+                unit,
+                delta,
+                modifiers,
+            });
+        }
         let delta = match delta {
             winit::event::MouseScrollDelta::LineDelta(x, y) => {
                 let points_per_scroll_line = 50.0; // Scroll speed decided by consensus: https://github.com/emilk/egui/issues/461

crates/egui/src/data/input.rs

@@ -278,6 +278,22 @@ pub enum Event {
         force: f32,
     },
 
+    /// A raw mouse wheel event as sent by the backend (minus the z coordinate),
+    /// for implementing alternative custom controls.
+    /// Note that the same event can also trigger [`Self::Zoom`] and [`Self::Scroll`],
+    /// so you probably want to handle only one of them.
+    MouseWheel {
+        /// The unit of scrolling: points, lines, or pages.
+        unit: MouseWheelUnit,
+
+        /// The amount scrolled horizontally and vertically. The amount and direction corresponding
+        /// to one step of the wheel depends on the platform.
+        delta: Vec2,
+
+        /// The state of the modifier keys at the time of the event.
+        modifiers: Modifiers,
+    },
+
     /// An assistive technology (e.g. screen reader) requested an action.
     #[cfg(feature = "accesskit")]
     AccessKitActionRequest(accesskit::ActionRequest),
@@ -891,6 +907,20 @@ pub enum TouchPhase {
     Cancel,
 }
 
+/// The unit associated with the numeric value of a mouse wheel event
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub enum MouseWheelUnit {
+    /// Number of ui points (logical pixels)
+    Point,
+
+    /// Number of lines
+    Line,
+
+    /// Number of pages
+    Page,
+}
+
 impl From<u64> for TouchId {
     fn from(id: u64) -> Self {
         Self(id)