Report mouse motion before click

This fixes an issue on macOS where a mouse click would be generated,
without ever getting a mouse motion to the position before the click.
This leads to the application thinking the mouse click occurred at a
position other than the actual mouse location.

This happens due to mouse motion above the window not automatically
giving focus to the window, unless it is actually clicked, making it
possible to move the window without motion events.

Fixes rust-windowing#942.

Author: chrisduerr

CHANGELOG.md

@@ -9,6 +9,7 @@
 - On Web, add the ability to query "Light" or "Dark" system theme send `ThemeChanged` on change.
 - Fix `Event::to_static` returning `None` for user events.
 - On Wayland, Hide CSD for fullscreen windows.
+- On macOS, a mouse motion event is now generated before every mouse click.
 
 # 0.21.0 (2020-02-04)
 

src/platform_impl/macos/view.rs

@@ -841,26 +841,32 @@ fn mouse_click(this: &Object, event: id, button: MouseButton, button_state: Elem
 }
 
 extern "C" fn mouse_down(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
     mouse_click(this, event, MouseButton::Left, ElementState::Pressed);
 }
 
 extern "C" fn mouse_up(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
     mouse_click(this, event, MouseButton::Left, ElementState::Released);
 }
 
 extern "C" fn right_mouse_down(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
     mouse_click(this, event, MouseButton::Right, ElementState::Pressed);
 }
 
 extern "C" fn right_mouse_up(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
     mouse_click(this, event, MouseButton::Right, ElementState::Released);
 }
 
 extern "C" fn other_mouse_down(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
     mouse_click(this, event, MouseButton::Middle, ElementState::Pressed);
 }
 
 extern "C" fn other_mouse_up(this: &Object, _sel: Sel, event: id) {
+    mouse_motion(this, event);
     mouse_click(this, event, MouseButton::Middle, ElementState::Released);
 }