Revert "```"

This reverts commit 5b4aebd.

Author: DylanHuang

src/vsg/app/Trackball.cpp

@@ -302,45 +302,43 @@ void Trackball::apply(TouchDownEvent& touchDown)
     if (!eventRelevant(touchDown)) return;
 
     _previousTouches[touchDown.id] = &touchDown;
-
-    // First touch - simulate button press for rotation
-    if (_previousTouches.size() == 1)
+    switch (touchDown.id)
     {
-        vsg::ref_ptr<vsg::Window> w = touchDown.window;
-        vsg::ref_ptr<vsg::ButtonPressEvent> evt = vsg::ButtonPressEvent::create(
-            w,
-            touchDown.time,
-            touchDown.x,
-            touchDown.y,
-            touchMappedToButtonMask,
-            touchDown.id);
-        apply(*evt.get());
+    case 0: {
+        if (_previousTouches.size() == 1)
+        {
+            vsg::ref_ptr<vsg::Window> w = touchDown.window;
+            vsg::ref_ptr<vsg::ButtonPressEvent> evt = vsg::ButtonPressEvent::create(
+                w,
+                touchDown.time,
+                touchDown.x,
+                touchDown.y,
+                touchMappedToButtonMask,
+                touchDown.id);
+            apply(*evt.get());
+        }
+        break;
+    }
+    case 1: {
+        _prevZoomTouchDistance = 0.0;
+        if (touchDown.id == 0 && _previousTouches.count(1))
+        {
+            const auto& prevTouch1 = _previousTouches[1];
+            auto a = std::abs(static_cast<double>(prevTouch1->x) - touchDown.x);
+            auto b = std::abs(static_cast<double>(prevTouch1->y) - touchDown.y);
+            if (a > 0 || b > 0)
+                _prevZoomTouchDistance = sqrt(a * a + b * b);
+        }
+        break;
     }
-    // Second touch - initialize zoom distance
-    else if (_previousTouches.size() == 2)
-    {
-        // Calculate initial distance between the two touches
-        auto it = _previousTouches.begin();
-        const TouchEvent* touch1 = it->second;
-        ++it;
-        const TouchEvent* touch2 = it->second;
-
-        auto a = std::abs(static_cast<double>(touch1->x) - static_cast<double>(touch2->x));
-        auto b = std::abs(static_cast<double>(touch1->y) - static_cast<double>(touch2->y));
-        _prevZoomTouchDistance = sqrt(a * a + b * b);
-
-        // Reset zoom state to establish a stable baseline
-        // This prevents immediate zoom when second finger touches
-        _zoomPreviousRatio = 0.0;
     }
 }
 
 void Trackball::apply(TouchUpEvent& touchUp)
 {
     if (!eventRelevant(touchUp)) return;
 
-    // If this is the last touch, simulate button release
-    if (_previousTouches.size() == 1)
+    if (touchUp.id == 0 && _previousTouches.size() == 1)
     {
         vsg::ref_ptr<vsg::Window> w = touchUp.window;
         vsg::ref_ptr<vsg::ButtonReleaseEvent> evt = vsg::ButtonReleaseEvent::create(
@@ -374,73 +372,24 @@ void Trackball::apply(TouchMoveEvent& touchMove)
         break;
     }
     case 2: {
-        // Two touches - Zoom by pinch
-        // Find the other touch (not the current moving one)
-        const TouchEvent* otherTouch = nullptr;
-
-        // Iterate through the map to find the touch that isn't the current one
-        for (const auto& [id, touch] : _previousTouches)
+        if (touchMove.id == 0 && _previousTouches.count(0))
         {
-            if (id != touchMove.id)
+            // Zoom
+            const auto& prevTouch1 = _previousTouches[1];
+            auto a = std::abs(static_cast<double>(prevTouch1->x) - touchMove.x);
+            auto b = std::abs(static_cast<double>(prevTouch1->y) - touchMove.y);
+            if (a > 0 || b > 0)
             {
-                otherTouch = touch;
-                break;
-            }
-        }
-
-        if (otherTouch)
-        {
-            // Calculate current distance between two touches
-            auto a = std::abs(static_cast<double>(otherTouch->x) - touchMove.x);
-            auto b = std::abs(static_cast<double>(otherTouch->y) - touchMove.y);
-            auto currentDistance = sqrt(a * a + b * b);
-
-            // Only process zoom if we have a valid previous distance
-            if (_prevZoomTouchDistance > 0 && currentDistance > 0)
-            {
-                // Calculate the distance change
-                auto distanceChange = std::abs(currentDistance - _prevZoomTouchDistance);
-
-                // Minimum threshold to prevent jitter (e.g., 5 pixels)
-                // Adjust this value based on screen DPI and desired sensitivity
-                constexpr double MIN_ZOOM_THRESHOLD = 5.0;
-
-                if (distanceChange >= MIN_ZOOM_THRESHOLD)
+                auto touchZoomDistance = sqrt(a * a + b * b);
+                if (_prevZoomTouchDistance && touchZoomDistance > 0)
                 {
-                    // Calculate zoom ratio
-                    auto zoomRatio = currentDistance / _prevZoomTouchDistance;
-
-                    // Dead zone: ignore tiny changes near 1.0 (e.g., 0.98-1.02)
-                    constexpr double DEAD_ZONE_MIN = 0.98;
-                    constexpr double DEAD_ZONE_MAX = 1.02;
-
-                    if (zoomRatio < DEAD_ZONE_MIN || zoomRatio > DEAD_ZONE_MAX)
-                    {
-                        // Clamp extreme zoom values to prevent sudden jumps
-                        // Limit to 0.5x - 2.0x per frame
-                        constexpr double MIN_ZOOM_RATIO = 0.5;
-                        constexpr double MAX_ZOOM_RATIO = 2.0;
-                        zoomRatio = std::clamp(zoomRatio, MIN_ZOOM_RATIO, MAX_ZOOM_RATIO);
-
-                        // Convert ratio to zoom level
-                        auto zoomLevel = zoomRatio;
-                        if (zoomLevel < 1.0)
-                            zoomLevel = -(1.0 / zoomLevel);
-
-                        // Apply zoom with damping factor (0.1 = 10% of calculated zoom)
-                        // This makes zoom feel smoother and more controllable
-                        zoomLevel *= 0.1;
-                        zoom(zoomLevel);
-                        vsg::debug("zoom event - distanceChange: ", distanceChange, ", zoomRatio: ", zoomRatio, ", zoomLevel: ", zoomLevel);
-                        // Update previous distance for next frame
-                        _prevZoomTouchDistance = currentDistance;
-                    }
+                    auto zoomLevel = touchZoomDistance / _prevZoomTouchDistance;
+                    if (zoomLevel < 1)
+                        zoomLevel = -(1 / zoomLevel);
+                    zoomLevel *= 0.1;
+                    zoom(zoomLevel);
                 }
-            }
-            else
-            {
-                // First valid measurement, just store the distance
-                _prevZoomTouchDistance = currentDistance;
+                _prevZoomTouchDistance = touchZoomDistance;
             }
         }
         break;