Implement web_sys::Canvas event listeners

src/platform_impl/web/web_sys/event.rs

@@ -0,0 +1,41 @@
+use crate::dpi::LogicalPosition;
+use crate::event::{ModifiersState, MouseButton, MouseScrollDelta};
+
+use std::convert::TryInto;
+use web_sys::{MouseEvent, WheelEvent};
+
+pub fn mouse_button(event: &MouseEvent) -> MouseButton {
+    match event.button() {
+        0 => MouseButton::Left,
+        1 => MouseButton::Middle,
+        2 => MouseButton::Right,
+        i => MouseButton::Other((i - 3).try_into().expect("very large mouse button value")),
+    }
+}
+
+pub fn mouse_modifiers(event: &MouseEvent) -> ModifiersState {
+    ModifiersState {
+        shift: event.shift_key(),
+        ctrl: event.ctrl_key(),
+        alt: event.alt_key(),
+        logo: event.meta_key(),
+    }
+}
+
+pub fn mouse_position(event: &MouseEvent) -> LogicalPosition {
+    LogicalPosition {
+        x: event.offset_x() as f64,
+        y: event.offset_y() as f64,
+    }
+}
+
+pub fn mouse_scroll_delta(event: &WheelEvent) -> Option<MouseScrollDelta> {
+    let x = event.delta_x();
+    let y = event.delta_y();
+
+    match event.delta_mode() {
+        WheelEvent::DOM_DELTA_LINE => Some(MouseScrollDelta::LineDelta(x as f32, y as f32)),
+        WheelEvent::DOM_DELTA_PIXEL => Some(MouseScrollDelta::PixelDelta(LogicalPosition { x, y })),
+        _ => None,
+    }
+}