fix KnobEventHandler when used on touchscreens

1 files changed, 6 insertions, 4 deletions

diff --git a/src/widget/knobeventhandler.h b/src/widget/knobeventhandler.h
index f06fbc26ce..5ab63c85df 100644
--- a/src/widget/knobeventhandler.h
+++ b/src/widget/knobeventhandler.h
@@ -22,13 +22,13 @@ class KnobEventHandler {
 
     double valueFromMouseEvent(T* pWidget, QMouseEvent* e) {
         QPoint cur(e->globalPos());
-        QPoint diff(cur - m_startPos);
+        QPoint diff(cur - m_prevPos);
         double dist = sqrt(static_cast<double>(diff.x() * diff.x() + diff.y() * diff.y()));
         bool y_dominant = abs(diff.y()) > abs(diff.x());
 
-        // if y is dominant, then thread an increase in dy as negative (y is
+        // if y is dominant, then treat an increase in dy as negative (y is
         // pointed downward). Otherwise, if y is not dominant and x has
-        // decreased, then thread it as negative.
+        // decreased, then treat it as negative.
         if ((y_dominant && diff.y() > 0) || (!y_dominant && diff.x() < 0)) {
             dist = -dist;
         }
@@ -44,10 +44,10 @@ class KnobEventHandler {
 
     void mouseMoveEvent(T* pWidget, QMouseEvent* e) {
         if (!m_bRightButtonPressed) {
-            QCursor::setPos(m_startPos);
             double value = valueFromMouseEvent(pWidget, e);
             pWidget->setControlParameterDown(value);
             pWidget->inputActivity();
+            m_prevPos = e->globalPos();
         }
     }
 
@@ -60,6 +60,7 @@ class KnobEventHandler {
             case Qt::LeftButton:
             case Qt::MiddleButton:
                 m_startPos = e->globalPos();
+                m_prevPos = m_startPos;
                 // Somehow using Qt::BlankCursor does not work on Windows
                 // https://mixxx.org/forums/viewtopic.php?p=40298#p40298
                 QApplication::setOverrideCursor(m_blankCursor);
@@ -107,5 +108,6 @@ class KnobEventHandler {
 
     // Starting point when left mouse button is pressed
     QPoint m_startPos;
+    QPoint m_prevPos;
     QCursor m_blankCursor;
 };