diff widgets/WheelCounter.h @ 1303:13f5f84fbfad

Collect the bits of bookkeeping for mouse wheel events, and use in all widgets

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widgets/WheelCounter.h	Fri Jun 22 17:19:48 2018 +0100
@@ -0,0 +1,65 @@
+/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
+
+/*
+    Sonic Visualiser
+    An audio file viewer and annotation editor.
+    Centre for Digital Music, Queen Mary, University of London.
+    
+    This program is free software; you can redistribute it and/or
+    modify it under the terms of the GNU General Public License as
+    published by the Free Software Foundation; either version 2 of the
+    License, or (at your option) any later version.  See the file
+    COPYING included with this distribution for more information.
+*/
+
+#ifndef SV_WHEEL_COUNTER_H
+#define SV_WHEEL_COUNTER_H
+
+#include <QWheelEvent>
+
+/**
+ * Manage the little bit of tedious book-keeping associated with
+ * translating vertical wheel events into up/down notch counts
+ */
+class WheelCounter
+{
+public:
+    WheelCounter() : m_pendingWheelAngle(0) { }
+
+    ~WheelCounter() { }
+
+    int count(QWheelEvent *e) {
+        
+        e->accept();
+    
+        int delta = e->angleDelta().y();
+        if (delta == 0) {
+            return 0;
+        }
+
+        if (e->phase() == Qt::ScrollBegin ||
+            std::abs(delta) >= 120 ||
+            (delta > 0 && m_pendingWheelAngle < 0) ||
+            (delta < 0 && m_pendingWheelAngle > 0)) {
+            m_pendingWheelAngle = delta;
+        } else {
+            m_pendingWheelAngle += delta;
+        }
+
+        if (abs(m_pendingWheelAngle) >= 600) {
+            // Sometimes on Linux we're seeing absurdly extreme angles
+            // on the first wheel event -- discard those entirely
+            m_pendingWheelAngle = 0;
+            return 0;
+        }
+
+        int count = m_pendingWheelAngle / 120;
+        m_pendingWheelAngle -= count * 120;
+        return count;
+    }
+
+private:
+    int m_pendingWheelAngle;
+};
+
+#endif