Merge pull request rust-windowing#336 from Veedrac/hidpi_fix

Fix non-integer HiDPI support in demo

Author: pcwalton

demo/common/src/lib.rs

@@ -461,7 +461,7 @@ impl<W> DemoApp<W> where W: Window {
     }
 
     fn process_mouse_position(&mut self, new_position: Vector2I) -> MousePosition {
-        let absolute = new_position * self.window_size.backing_scale_factor as i32;
+        let absolute = (new_position.to_f32() * self.window_size.backing_scale_factor).to_i32();
         let relative = absolute - self.last_mouse_position;
         self.last_mouse_position = absolute;
         MousePosition { absolute, relative }