fix(macOS): correct right and middle mouse drag handling

src/platform/macos/macos_backend.cpp

@@ -531,6 +531,14 @@ namespace lvh::detail {
       CGEventType up_event {};  ///< CoreGraphics up event type.
     };
 
+    /**
+     * @brief CoreGraphics metadata for a mouse motion event.
+     */
+    struct MacosMouseMotion {
+      CGMouseButton button {};  ///< CoreGraphics button associated with the motion.
+      CGEventType event_type {};  ///< CoreGraphics motion event type.
+    };
+
     /**
      * @brief Translate a portable mouse button to CoreGraphics metadata.
      *
@@ -555,6 +563,25 @@ namespace lvh::detail {
       return std::nullopt;
     }
 
+    /**
+     * @brief Select CoreGraphics motion metadata for the currently held mouse buttons.
+     *
+     * @param mouse_down Local left, right, and middle button state.
+     * @return Matching CoreGraphics button and motion event type.
+     */
+    inline MacosMouseMotion macos_mouse_motion(const std::array<bool, 3> &mouse_down) {
+      if (mouse_down[0]) {
+        return {kCGMouseButtonLeft, kCGEventLeftMouseDragged};
+      }
+      if (mouse_down[1]) {
+        return {kCGMouseButtonRight, kCGEventRightMouseDragged};
+      }
+      if (mouse_down[2]) {
+        return {kCGMouseButtonCenter, kCGEventOtherMouseDragged};
+      }
+      return {kCGMouseButtonLeft, kCGEventMouseMoved};
+    }
+
     /**
      * @brief Backend mouse backed by CoreGraphics mouse and scroll events.
      */
@@ -613,19 +640,6 @@ namespace lvh::detail {
         return current;
       }
 
-      CGEventType event_type_for_current_buttons() const {
-        if (mouse_down_[0]) {
-          return kCGEventLeftMouseDragged;
-        }
-        if (mouse_down_[1]) {
-          return kCGEventOtherMouseDragged;
-        }
-        if (mouse_down_[2]) {
-          return kCGEventRightMouseDragged;
-        }
-        return kCGEventMouseMoved;
-      }
-
       OperationStatus post_mouse(
         CGMouseButton button,
         CGEventType type,
@@ -660,13 +674,15 @@ namespace lvh::detail {
       OperationStatus submit_relative_motion(std::int32_t delta_x, std::int32_t delta_y) {
         const auto current = current_location();
         const auto location = CGPoint {current.x + delta_x, current.y + delta_y};
-        return post_mouse(kCGMouseButtonLeft, event_type_for_current_buttons(), location, current, 0);
+        const auto motion = macos_mouse_motion(mouse_down_);
+        return post_mouse(motion.button, motion.event_type, location, current, 0);
       }
 
       OperationStatus submit_absolute_motion(const MouseEvent &event) {
         const auto display_bounds = CGDisplayBounds(state_->display);
         const auto location = absolute_mouse_location(event, display_bounds);
-        return post_mouse(kCGMouseButtonLeft, event_type_for_current_buttons(), location, current_location(), 0);
+        const auto motion = macos_mouse_motion(mouse_down_);
+        return post_mouse(motion.button, motion.event_type, location, current_location(), 0);
       }
 
       OperationStatus submit_button(const MouseEvent &event) {

tests/fixtures/include/fixtures/macos_backend_test_hooks.hpp

@@ -21,6 +21,14 @@ namespace lvh::detail::test {
     double y {};  ///< Vertical coordinate.
   };
 
+  /**
+   * @brief Portable representation of CoreGraphics mouse motion metadata for tests.
+   */
+  struct MacosMouseMotionResult {
+    std::uint32_t button {};  ///< CoreGraphics mouse button value.
+    std::uint32_t event_type {};  ///< CoreGraphics mouse event type value.
+  };
+
   /**
    * @brief Result set for macOS backend lifecycle utility coverage.
    */
@@ -93,6 +101,16 @@ namespace lvh::detail::test {
     double height
   );
 
+  /**
+   * @brief Select CoreGraphics motion metadata for a mouse button state.
+   *
+   * @param left_down Whether the left button is held.
+   * @param right_down Whether the right button is held.
+   * @param middle_down Whether the middle button is held.
+   * @return CoreGraphics button and motion event type values.
+   */
+  MacosMouseMotionResult macos_backend_mouse_motion(bool left_down, bool right_down, bool middle_down);
+
   /**
    * @brief Exercise macOS backend creation and unsupported-device paths.
    *

tests/fixtures/macos_backend_test_hooks.cpp

@@ -56,6 +56,14 @@ namespace lvh::detail::test {
     return {.x = location.x, .y = location.y};
   }
 
+  MacosMouseMotionResult macos_backend_mouse_motion(bool left_down, bool right_down, bool middle_down) {
+    const auto motion = macos::macos_mouse_motion({left_down, right_down, middle_down});
+    return {
+      .button = static_cast<std::uint32_t>(motion.button),
+      .event_type = static_cast<std::uint32_t>(motion.event_type),
+    };
+  }
+
   MacosBackendUtilityResult macos_backend_utilities() {
     auto backend = create_platform_backend_for_macos_backend_test_hooks();
     MacosBackendUtilityResult result;

tests/unit/test_macos_backend.cpp

@@ -104,6 +104,26 @@ TEST_F(MacosBackendTest, ConvertsAbsoluteMouseCoordinates) {
   EXPECT_DOUBLE_EQ(location.y, 170.0);
 }
 
+TEST_F(MacosBackendTest, SelectsMouseMotionMetadataForHeldButtons) {
+  using lvh::detail::test::macos_backend_mouse_motion;
+
+  auto motion = macos_backend_mouse_motion(false, false, false);
+  EXPECT_EQ(motion.button, kCGMouseButtonLeft);
+  EXPECT_EQ(motion.event_type, kCGEventMouseMoved);
+
+  motion = macos_backend_mouse_motion(true, false, false);
+  EXPECT_EQ(motion.button, kCGMouseButtonLeft);
+  EXPECT_EQ(motion.event_type, kCGEventLeftMouseDragged);
+
+  motion = macos_backend_mouse_motion(false, true, false);
+  EXPECT_EQ(motion.button, kCGMouseButtonRight);
+  EXPECT_EQ(motion.event_type, kCGEventRightMouseDragged);
+
+  motion = macos_backend_mouse_motion(false, false, true);
+  EXPECT_EQ(motion.button, kCGMouseButtonCenter);
+  EXPECT_EQ(motion.event_type, kCGEventOtherMouseDragged);
+}
+
 TEST_F(MacosBackendTest, ReportsCapabilitiesAndUnsupportedDevices) {
   const auto result = lvh::detail::test::macos_backend_utilities();