ui: scale wheel lines on Windows/Linux to Mac (#14395)

* input: accelerate wheel bursts on Windows->Mac

- boost fast wheel bursts without affecting single-step scrolls\n- use dominant-axis smooth detection and velocity gate\n- reset wheel timestamp on enter/leave\n- enforce single-axis scrolling\n- extract/tune Sciter wheel accel thresholds

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

* input: clarify wheel burst tuning

- add comments on acceleration rules and units\n- apply burst accel on Windows/Linux to macOS\n- reset wheel timing on enter/leave

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

* input: align wheel burst velocity thresholds

- match Flutter velocity gate with Sciter

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

* input: restore flutter wheel velocity threshold

- keep burst threshold at 0.002 delta/us

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

---------

Signed-off-by: Amirhossein Akhlaghpour <m9.akhlaghpoor@gmail.com>

flutter/lib/models/input_model.dart

@@ -365,6 +365,16 @@ class InputModel {
   final isPhysicalMouse = false.obs;
   int _lastButtons = 0;
   Offset lastMousePos = Offset.zero;
+  int _lastWheelTsUs = 0;
+
+  // Wheel acceleration thresholds.
+  static const int _wheelAccelFastThresholdUs = 40000; // 40ms
+  static const int _wheelAccelMediumThresholdUs = 80000; // 80ms
+  static const double _wheelBurstVelocityThreshold =
+      0.002; // delta units per microsecond
+  // Wheel burst acceleration (empirical tuning).
+  // Applies only to fast, non-smooth bursts to preserve single-step scrolling.
+  // Flutter uses microseconds for dt, so velocity is in delta/us.
 
   // Relative mouse mode (for games/3D apps).
   final relativeMouseMode = false.obs;
@@ -964,6 +974,7 @@ class InputModel {
     toReleaseRawKeys.release(handleRawKeyEvent);
     _pointerMovedAfterEnter = false;
     _pointerInsideImage = enter;
+    _lastWheelTsUs = 0;
 
     // Fix status
     if (!enter) {
@@ -1407,17 +1418,44 @@ class InputModel {
     if (isViewOnly) return;
     if (isViewCamera) return;
     if (e is PointerScrollEvent) {
-      var dx = e.scrollDelta.dx.toInt();
+      final rawDx = e.scrollDelta.dx;
-      var dy = e.scrollDelta.dy.toInt();
+      final rawDy = e.scrollDelta.dy;
+      final dominantDelta = rawDx.abs() > rawDy.abs() ? rawDx.abs() : rawDy.abs();
+      final isSmooth = dominantDelta < 1;
+      final nowUs = DateTime.now().microsecondsSinceEpoch;
+      final dtUs = _lastWheelTsUs == 0 ? 0 : nowUs - _lastWheelTsUs;
+      _lastWheelTsUs = nowUs;
+      int accel = 1;
+      if (!isSmooth &&
+          dtUs > 0 &&
+          dtUs <= _wheelAccelMediumThresholdUs &&
+          (isWindows || isLinux) &&
+          peerPlatform == kPeerPlatformMacOS) {
+        final velocity = dominantDelta / dtUs;
+        if (velocity >= _wheelBurstVelocityThreshold) {
+          if (dtUs < _wheelAccelFastThresholdUs) {
+            accel = 3;
+          } else {
+            accel = 2;
+          }
+        }
+      }
+      var dx = rawDx.toInt();
+      var dy = rawDy.toInt();
+      if (rawDx.abs() > rawDy.abs()) {
+        dy = 0;
+      } else {
+        dx = 0;
+      }
       if (dx > 0) {
-        dx = -1;
+        dx = -accel;
       } else if (dx < 0) {
-        dx = 1;
+        dx = accel;
       }
       if (dy > 0) {
-        dy = -1;
+        dy = -accel;
       } else if (dy < 0) {
-        dy = 1;
+        dy = accel;
       }
       bind.sessionSendMouse(
           sessionId: sessionId,

src/ui/remote.tis

@@ -142,6 +142,14 @@ function resetWheel() {
 }
 
 var INERTIA_ACCELERATION = 30;
+var WHEEL_ACCEL_VELOCITY_THRESHOLD = 5000;
+var WHEEL_ACCEL_DT_FAST = 0.04;
+var WHEEL_ACCEL_DT_MEDIUM = 0.08;
+var WHEEL_ACCEL_VALUE_FAST = 3;
+var WHEEL_ACCEL_VALUE_MEDIUM = 2;
+// Wheel burst acceleration (empirical tuning).
+// Applies only on fast, non-smooth wheel bursts to keep single-step scroll unchanged.
+// Sciter uses seconds for dt, so velocity is in delta/sec.
 
 // not good, precision not enough to simulate acceleration effect,
 // seems have to use pixel based rather line based delta
@@ -237,12 +245,28 @@ function handler.onMouse(evt)
         // mouseWheelDistance = 8 * [currentUserDefs floatForKey:@"com.apple.scrollwheel.scaling"];
         mask = 3; 
         {
-            var (dx, dy) = evt.wheelDeltas;
+            var now = getTime();
-            if (dx > 0) dx = 1;
+            var dt = last_wheel_time > 0 ? (now - last_wheel_time) / 1000 : 0;
-            else if (dx < 0) dx = -1;
+            var (raw_dx, raw_dy) = evt.wheelDeltas;
-            if (dy > 0) dy = 1;
+            var dx = 0;
-            else if (dy < 0) dy = -1;
+            var dy = 0;
-            if (Math.abs(dx) > Math.abs(dy)) {
+            var abs_dx = Math.abs(raw_dx);
+            var abs_dy = Math.abs(raw_dy);
+            var dominant = abs_dx > abs_dy ? abs_dx : abs_dy;
+            var is_smooth = dominant < 1;
+            var accel = 1;
+            if (!is_smooth && dt > 0 && (is_win || is_linux) && get_peer_platform() == "Mac OS") {
+                var velocity = dominant / dt;
+                if (velocity >= WHEEL_ACCEL_VELOCITY_THRESHOLD) {
+                    if (dt < WHEEL_ACCEL_DT_FAST) accel = WHEEL_ACCEL_VALUE_FAST;
+                    else if (dt < WHEEL_ACCEL_DT_MEDIUM) accel = WHEEL_ACCEL_VALUE_MEDIUM;
+                }
+            }
+            if (raw_dx > 0) dx = accel;
+            else if (raw_dx < 0) dx = -accel;
+            if (raw_dy > 0) dy = accel;
+            else if (raw_dy < 0) dy = -accel;
+            if (abs_dx > abs_dy) {
                 dy = 0;
             } else {
                 dx = 0;
@@ -253,8 +277,6 @@ function handler.onMouse(evt)
             wheel_delta_y = acc_wheel_delta_y.toInteger();
             acc_wheel_delta_x -= wheel_delta_x;
             acc_wheel_delta_y -= wheel_delta_y;
-            var now = getTime();
-            var dt = last_wheel_time > 0 ? (now - last_wheel_time) / 1000 : 0;
             if (dt > 0) {
                 var vx = dx / dt;
                 var vy = dy / dt;
@@ -297,11 +319,13 @@ function handler.onMouse(evt)
         entered = true;
         stdout.println("enter");
         handler.enter(handler.get_keyboard_mode());
+        last_wheel_time = 0;
         return keyboard_enabled;
       case Event.MOUSE_LEAVE:
         entered = false;
         stdout.println("leave");
         handler.leave(handler.get_keyboard_mode());
+        last_wheel_time = 0;
         if (is_left_down && get_peer_platform() == "Android") {
             is_left_down = false;
             handler.send_mouse((1 << 3) | 2, 0, 0, evt.altKey,