feat: Add relative mouse mode (#13928)

* feat: Add relative mouse mode

- Add "Relative Mouse Mode" toggle in desktop toolbar and bind to InputModel
- Implement relative mouse movement path: Flutter pointer deltas -> `type: move_relative` -> new `MOUSE_TYPE_MOVE_RELATIVE` in Rust
- In server input service, simulate relative movement via Enigo and keep latest cursor position in sync
- Track pointer-lock center in Flutter (local widget + screen coordinates) and re-center OS cursor after each relative move
- Update pointer-lock center on window move/resize/restore/maximize and when remote display geometry changes
- Hide local cursor when relative mouse mode is active (both Flutter cursor and OS cursor), restore on leave/disable
- On Windows, clip OS cursor to the window rect while in relative mode and release clip when leaving/turning off
- Implement platform helpers: `get_cursor_pos`, `set_cursor_pos`, `show_cursor`, `clip_cursor` (no-op clip/hide on Linux for now)
- Add keyboard shortcut Ctrl+Alt+Shift+M to toggle relative mode (enabled by default, works on all platforms)
- Remove `enable-relative-mouse-shortcut` config option - shortcut is now always available when keyboard permission is granted
- Handle window blur/focus/minimize events to properly release/restore cursor constraints
- Add MOUSE_TYPE_MASK constant and unit tests for mouse event constants

Note: Relative mouse mode state is NOT persisted to config (session-only).
Note: On Linux, show_cursor and clip_cursor are no-ops; cursor hiding is handled by Flutter side.

Signed-off-by: fufesou <linlong1266@gmail.com>

* feat(mouse): relative mouse mode, exit hint

Signed-off-by: fufesou <linlong1266@gmail.com>

* refact(relative mouse): shortcut

Signed-off-by: fufesou <linlong1266@gmail.com>

---------

Signed-off-by: fufesou <linlong1266@gmail.com>

src/common.rs

@@ -71,6 +71,19 @@ pub mod input {
     pub const MOUSE_TYPE_UP: i32 = 2;
     pub const MOUSE_TYPE_WHEEL: i32 = 3;
     pub const MOUSE_TYPE_TRACKPAD: i32 = 4;
+    /// Relative mouse movement type for gaming/3D applications.
+    /// This type sends delta (dx, dy) values instead of absolute coordinates.
+    /// NOTE: This is only supported by the Flutter client. The Sciter client (deprecated)
+    /// does not support relative mouse mode due to:
+    /// 1. Fixed send_mouse() function signature that doesn't allow type differentiation
+    /// 2. Lack of pointer lock API in Sciter/TIS
+    /// 3. No OS cursor control (hide/show/clip) FFI bindings in Sciter UI
+    pub const MOUSE_TYPE_MOVE_RELATIVE: i32 = 5;
+
+    /// Mask to extract the mouse event type from the mask field.
+    /// The lower 3 bits contain the event type (MOUSE_TYPE_*), giving a valid range of 0-7.
+    /// Currently defined types use values 0-5; values 6 and 7 are reserved for future use.
+    pub const MOUSE_TYPE_MASK: i32 = 0x7;
 
     pub const MOUSE_BUTTON_LEFT: i32 = 0x01;
     pub const MOUSE_BUTTON_RIGHT: i32 = 0x02;
@@ -175,6 +188,20 @@ pub fn is_support_file_transfer_resume_num(ver: i64) -> bool {
     ver >= hbb_common::get_version_number("1.4.2")
 }
 
+/// Minimum server version required for relative mouse mode support.
+/// This constant must mirror Flutter's `kMinVersionForRelativeMouseMode` in `consts.dart`.
+const MIN_VERSION_RELATIVE_MOUSE_MODE: &str = "1.4.5";
+
+#[inline]
+pub fn is_support_relative_mouse_mode(ver: &str) -> bool {
+    is_support_relative_mouse_mode_num(hbb_common::get_version_number(ver))
+}
+
+#[inline]
+pub fn is_support_relative_mouse_mode_num(ver: i64) -> bool {
+    ver >= hbb_common::get_version_number(MIN_VERSION_RELATIVE_MOUSE_MODE)
+}
+
 // is server process, with "--server" args
 #[inline]
 pub fn is_server() -> bool {
@@ -2462,4 +2489,36 @@ mod tests {
         assert!(!is_public("https://rustdesk.computer.com"));
         assert!(!is_public("rustdesk.comhello.com"));
     }
+
+    #[test]
+    fn test_mouse_event_constants_and_mask_layout() {
+        use super::input::*;
+
+        // Verify MOUSE_TYPE constants are unique and within the mask range.
+        let types = [
+            MOUSE_TYPE_MOVE,
+            MOUSE_TYPE_DOWN,
+            MOUSE_TYPE_UP,
+            MOUSE_TYPE_WHEEL,
+            MOUSE_TYPE_TRACKPAD,
+            MOUSE_TYPE_MOVE_RELATIVE,
+        ];
+
+        let mut seen = std::collections::HashSet::new();
+        for t in types.iter() {
+            assert!(seen.insert(*t), "Duplicate mouse type: {}", t);
+            assert_eq!(
+                *t & MOUSE_TYPE_MASK,
+                *t,
+                "Mouse type {} exceeds mask {}",
+                t,
+                MOUSE_TYPE_MASK
+            );
+        }
+
+        // The mask layout is: lower 3 bits for type, upper bits for buttons (shifted by 3).
+        let combined_mask = MOUSE_TYPE_DOWN | ((MOUSE_BUTTON_LEFT | MOUSE_BUTTON_RIGHT) << 3);
+        assert_eq!(combined_mask & MOUSE_TYPE_MASK, MOUSE_TYPE_DOWN);
+        assert_eq!(combined_mask >> 3, MOUSE_BUTTON_LEFT | MOUSE_BUTTON_RIGHT);
+    }
 }