Windows: Ignore spurious mouse move messages

Fixes rust-windowing#1428
filnet · Feb 5, 2020 · e25c4d8 · e25c4d8
1 parent e295104
commit e25c4d8
Show file tree

Hide file tree

Showing 3 changed files with 23 additions and 10 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -12,6 +12,7 @@
 - On Wayland, fix coordinates in mouse events when scale factor isn't 1
 - On Web, add the ability to provide a custom canvas
 - **Breaking:** On Wayland, the `WaylandTheme` struct has been replaced with a `Theme` trait, allowing for extra configuration
+- On Windows, ignore spurious mouse move messages.
 
 # 0.20.0 (2020-01-05)
 

diff --git a/src/platform_impl/windows/event_loop.rs b/src/platform_impl/windows/event_loop.rs
@@ -858,15 +858,25 @@ unsafe extern "system" fn public_window_callback<T: 'static>(
             let x = windowsx::GET_X_LPARAM(lparam) as f64;
             let y = windowsx::GET_Y_LPARAM(lparam) as f64;
             let position = PhysicalPosition::new(x, y);
-
-            subclass_input.send_event(Event::WindowEvent {
-                window_id: RootWindowId(WindowId(window)),
-                event: CursorMoved {
-                    device_id: DEVICE_ID,
-                    position,
-                    modifiers: event::get_key_mods(),
-                },
-            });
+            let cursor_moved;
+            {
+                // handle spurious WM_MOUSEMOVE messages
+                // see https://devblogs.microsoft.com/oldnewthing/20031001-00/?p=42343
+                // and http://debugandconquer.blogspot.com/2015/08/the-cause-of-spurious-mouse-move.html
+                let mut w = subclass_input.window_state.lock();
+                cursor_moved = w.mouse.last_position != Some(position);
+                w.mouse.last_position = Some(position);
+            }
+            if cursor_moved {
+                subclass_input.send_event(Event::WindowEvent {
+                    window_id: RootWindowId(WindowId(window)),
+                    event: CursorMoved {
+                        device_id: DEVICE_ID,
+                        position,
+                        modifiers: event::get_key_mods(),
+                    },
+                });
+            }
 
             0
         }

diff --git a/src/platform_impl/windows/window_state.rs b/src/platform_impl/windows/window_state.rs
@@ -1,5 +1,5 @@
 use crate::{
-    dpi::Size,
+    dpi::{PhysicalPosition, Size},
     platform_impl::platform::{event_loop, icon::WinIcon, util},
     window::{CursorIcon, Fullscreen, WindowAttributes},
 };
@@ -48,6 +48,7 @@ pub struct MouseProperties {
     pub cursor: CursorIcon,
     pub buttons_down: u32,
     cursor_flags: CursorFlags,
+    pub last_position: Option<PhysicalPosition<f64>>,
 }
 
 bitflags! {
@@ -106,6 +107,7 @@ impl WindowState {
                 cursor: CursorIcon::default(),
                 buttons_down: 0,
                 cursor_flags: CursorFlags::empty(),
+                last_position: None,
             },
 
             min_size: attributes.min_inner_size,