[fix] fix macOS remote keyboard modifier injection, fixes #81

src/device_controller/keyboard/mac/keyboard_capturer.cpp

@@ -269,10 +269,30 @@ inline bool IsFunctionKey(int key_code) {
   }
 }
 
+CGEventFlags ToCGEventFlags(uint32_t injected_flags) {
+  CGEventFlags flags = 0;
+  if ((injected_flags & kMacInjectedModifierShift) != 0) {
+    flags |= kCGEventFlagMaskShift;
+  }
+  if ((injected_flags & kMacInjectedModifierControl) != 0) {
+    flags |= kCGEventFlagMaskControl;
+  }
+  if ((injected_flags & kMacInjectedModifierOption) != 0) {
+    flags |= kCGEventFlagMaskAlternate;
+  }
+  if ((injected_flags & kMacInjectedModifierCommand) != 0) {
+    flags |= kCGEventFlagMaskCommand;
+  }
+  return flags;
+}
+
 int KeyboardCapturer::SendKeyboardCommand(int key_code, bool is_down,
                                           uint32_t scan_code, bool extended) {
   (void)scan_code;
   (void)extended;
+  const uint32_t injected_flags =
+      injected_modifier_state_.Update(key_code, is_down);
+
   if (vkCodeToCGKeyCode.find(key_code) != vkCodeToCGKeyCode.end()) {
     CGKeyCode cg_key_code = vkCodeToCGKeyCode[key_code];
     CGEventRef event = CGEventCreateKeyboardEvent(NULL, cg_key_code, is_down);
@@ -281,7 +301,7 @@ int KeyboardCapturer::SendKeyboardCommand(int key_code, bool is_down,
       return -1;
     }
 
-    CGEventSetFlags(event, 0);
+    CGEventSetFlags(event, ToCGEventFlags(injected_flags));
     CGEventPost(kCGHIDEventTap, event);
     CFRelease(event);
 

src/device_controller/keyboard/mac/keyboard_capturer.h

@@ -10,6 +10,7 @@
 #include <ApplicationServices/ApplicationServices.h>
 
 #include "device_controller.h"
+#include "macos_keyboard_modifier_state.h"
 
 namespace crossdesk {
 
@@ -36,6 +37,7 @@ class KeyboardCapturer : public DeviceController {
   bool option_flag_ = false;
   bool command_flag_ = false;
   int fn_key_code_ = 0x3F;
+  MacKeyboardModifierState injected_modifier_state_;
 };
 }  // namespace crossdesk
 #endif

src/device_controller/macos_keyboard_modifier_state.h

@@ -0,0 +1,93 @@
+/*
+ * @Author: DI JUNKUN
+ * @Date: 2026-05-21
+ * Copyright (c) 2026 by DI JUNKUN, All Rights Reserved.
+ */
+
+#ifndef _MACOS_KEYBOARD_MODIFIER_STATE_H_
+#define _MACOS_KEYBOARD_MODIFIER_STATE_H_
+
+#include <cstdint>
+
+namespace crossdesk {
+
+inline constexpr uint32_t kMacInjectedModifierShift = 1u << 0;
+inline constexpr uint32_t kMacInjectedModifierControl = 1u << 1;
+inline constexpr uint32_t kMacInjectedModifierOption = 1u << 2;
+inline constexpr uint32_t kMacInjectedModifierCommand = 1u << 3;
+
+class MacKeyboardModifierState {
+ public:
+  uint32_t Update(int key_code, bool is_down) {
+    bool* state = MutableStateForVk(key_code);
+    if (state != nullptr) {
+      *state = is_down;
+    }
+    return flags();
+  }
+
+  uint32_t flags() const {
+    uint32_t result = 0;
+    if (left_shift_down_ || right_shift_down_) {
+      result |= kMacInjectedModifierShift;
+    }
+    if (left_control_down_ || right_control_down_) {
+      result |= kMacInjectedModifierControl;
+    }
+    if (left_option_down_ || right_option_down_) {
+      result |= kMacInjectedModifierOption;
+    }
+    if (left_command_down_ || right_command_down_) {
+      result |= kMacInjectedModifierCommand;
+    }
+    return result;
+  }
+
+  void Clear() {
+    left_shift_down_ = false;
+    right_shift_down_ = false;
+    left_control_down_ = false;
+    right_control_down_ = false;
+    left_option_down_ = false;
+    right_option_down_ = false;
+    left_command_down_ = false;
+    right_command_down_ = false;
+  }
+
+ private:
+  bool* MutableStateForVk(int key_code) {
+    switch (key_code) {
+      case 0xA0:  // VK_LSHIFT
+        return &left_shift_down_;
+      case 0xA1:  // VK_RSHIFT
+        return &right_shift_down_;
+      case 0xA2:  // VK_LCONTROL
+        return &left_control_down_;
+      case 0xA3:  // VK_RCONTROL
+        return &right_control_down_;
+      case 0xA4:  // VK_LMENU / left Option
+        return &left_option_down_;
+      case 0xA5:  // VK_RMENU / right Option
+        return &right_option_down_;
+      case 0x5B:  // VK_LWIN / left Command
+        return &left_command_down_;
+      case 0x5C:  // VK_RWIN / right Command
+        return &right_command_down_;
+      default:
+        return nullptr;
+    }
+  }
+
+  bool left_shift_down_ = false;
+  bool right_shift_down_ = false;
+  bool left_control_down_ = false;
+  bool right_control_down_ = false;
+  bool left_option_down_ = false;
+  bool right_option_down_ = false;
+  bool left_command_down_ = false;
+  bool right_command_down_ = false;
+};
+
+}  // namespace crossdesk
+
+#endif