small refactoring to desktop navigation behavior

#463

demos/combustion_demo/src/desktop_navigation_behavior.cpp

@@ -75,25 +75,15 @@ void DesktopNavigationBehavior::OnMouseMove(int x, int y) {
 
 void DesktopNavigationBehavior::OnMouseButton(phx::Mouse::ButtonId id,
                                               phx::Mouse::ButtonEvent event) {
-  if (event == phx::Mouse::BUTTON_PRESSED) {
-    if (id == phx::Mouse::LEFT_BUTTON) {
-      rotation_mode_ = true;
-    }
-    if (id == phx::Mouse::MIDDLE_BUTTON) {
-      strafe_mode_ = true;
-    }
-    if (id == phx::Mouse::RIGHT_BUTTON) {
-      translation_mode_ = true;
-    }
-  } else {
+  bool value_to_set = (event == phx::Mouse::BUTTON_PRESSED);
+
   if (id == phx::Mouse::LEFT_BUTTON) {
-      rotation_mode_ = false;
+    rotation_mode_ = value_to_set;
   }
   if (id == phx::Mouse::MIDDLE_BUTTON) {
-      strafe_mode_ = false;
+    strafe_mode_ = value_to_set;
   }
   if (id == phx::Mouse::RIGHT_BUTTON) {
-      translation_mode_ = false;
-    }
+    translation_mode_ = value_to_set;
   }
 }