view widgets/WheelCounter.h @ 1534:bfd8b22fd67c

Fix #1904 Scrolling colour 3d plot does not always work when in View normalisation mode. We shouldn't imagine we've just invalidated the cache if the truth is that we've only just created the renderer

/* -*- 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