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Thread: Modifying QwtPlotMagnifier so it can handle touch events.

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  1. 27th February 2018, 18:05 #1
    ifhmcos
    ifhmcos is offline Beginner
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    Default Modifying QwtPlotMagnifier so it can handle touch events.

    Hello, I'm back with a small problem trying to use the QwtPlotMagnifier (its rescale function), I have modified it so it can handle touch events (pinch zooms) but I have a small problem I'm not understanding how to fix. I want to also zoom the axis step respectively. But the example uses just the scale intervals, and when I zoom the step gets set to a default value (I guess this is given by QwtScaleEngine?), I've tried to use a dumb rule of three to get a new scale but with no avail. (new_step = old_step / old_to_scale * new_to_scale).

    Qt Code: 
    1. struct scale {
    2.     float from;
    3.     float to;
    4.     float step;
    5. };
    6.  
    7. class zoom_filter : public QObject {
    8.     Q_OBJECT
    9.  
    10.     scale *x_scale, *y_scale;
    11.  
    12. public:
    13.     float *step, new_factor{1.0};
    14.     zoom_filter(QObject *p, scale *x_scale, scale *y_scale)
    15.         : QObject(p), x_scale(x_scale), y_scale(y_scale) {
    16.         p->installEventFilter(this);
    17.     }
    18.  
    19.     virtual bool eventFilter(QObject *o, QEvent *ev) {
    20.         // qDebug() << "Event called!";
    21.  
    22.         if (ev->type() == QEvent::Gesture) {
    23.             QGestureEvent *e = static_cast<QGestureEvent *>(ev);
    24.             if (QGesture *p = e->gesture(Qt::PinchGesture)) {
    25.                 qDebug() << "Pinch gesture";
    26.                 QPinchGesture *pinch = static_cast<QPinchGesture *>(p);
    27.                 if (pinch->changeFlags() & QPinchGesture::ScaleFactorChanged) {
    28.                     qDebug() << "Pinch zoom factor" << pinch->totalScaleFactor()
    29.                              << " " << pinch->scaleFactor();
    30.                     rescale(pinch->scaleFactor(), pinch->centerPoint(),
    31.                             ((QWidget *)parent())->size());
    32.                     new_factor = pinch->scaleFactor();
    33.                 }
    34.             } else if (QGesture *p = e->gesture(Qt::SwipeGesture)) {
    35.                 qDebug() << "Swipe gesture";
    36.             }
    37.         } else if (ev->type() == QEvent::Resize) {
    38.             qDebug() << "Rsize event";
    39.         }
    40.  
    41.         return QObject::eventFilter(o, ev);
    42.     }
    43.  
    44.     QwtPlot *plot() {
    45.         QWidget *w = qobject_cast<QWidget *>(parent());
    46.  
    47.         if (w)
    48.             w = w->parentWidget();
    49.  
    50.         return qobject_cast<QwtPlot *>(w);
    51.     }
    52.  
    53.     virtual void rescale(double factor, QPointF pos, QSize screen_size) {
    54.         QwtPlot *plt = plot();
    55.         if (plt == NULL)
    56.             return;
    57.  
    58.         factor = qAbs(factor);
    59.         if (factor == 1.0 || factor == 0.0)
    60.             return;
    61.  
    62.         for (int axisId = 0; axisId < QwtPlot::axisCnt; axisId++) {
    63.  
    64.             if (axisId == QwtPlot::xBottom || axisId == QwtPlot::yLeft) {
    65.                 const QwtScaleMap scaleMap = plt->canvasMap(axisId);
    66.  
    67.                 double v1 = scaleMap.s1();
    68.                 double v2 = scaleMap.s2();
    69.  
    70.                 if (scaleMap.transformation()) {
    71.                     // the coordinate system of the paint device is always linear
    72.                     v1 = scaleMap.transform(v1); // scaleMap.p1()
    73.                     v2 = scaleMap.transform(v2); // scaleMap.p2()
    74.                 }
    75.  
    76.                 double center = 0.5 * (v1 + v2);
    77.                 const double width_2 = 0.5 * (v2 - v1) * factor;
    78.  
    79.                 if (axisId == QwtPlot::yLeft)
    80.                     center = pos.y() / (float)screen_size.height() *
    81.                              v2; // 0.5 * ( v1 + v2 );
    82.                 else if (axisId == QwtPlot::xBottom)
    83.                     center = pos.x() / (float)screen_size.width() * v2; // v2;
    84.                 else
    85.                     continue;
    86.  
    87.                 v1 = center - width_2;
    88.                 v2 = center + width_2;
    89.  
    90.                 if (scaleMap.transformation()) {
    91.                     v1 = scaleMap.invTransform(v1);
    92.                     v2 = scaleMap.invTransform(v2);
    93.                 }
    94.  
    95.                 float sstep;
    96.                 // x_scale and y_scale got the initial scales and get updated accordingly
    97.                 if (axisId == QwtPlot::xBottom) {
    98.                     x_scale->step = v2 * x_scale->step / x_scale->to;
    99.                     sstep = x_scale->step;
    100.                     x_scale->to = v2;
    101.                     x_scale->from = v1;
    102.                 } else if (axisId == QwtPlot::yLeft) {
    103.                     float sscale = v2 / x_scale->to;
    104.                     qDebug() << "X sc " << factor << sscale << v2
    105.                              << y_scale->step << y_scale->to;
    106.  
    107.                     y_scale->step = v2 * y_scale->step / y_scale->to;
    108.                     sstep = y_scale->step;
    109.                     y_scale->to = v2;
    110.                     y_scale->from = v1;
    111.                 }
    112.  
    113.                 // The step is not working as intended
    114.                 plt->setAxisScale(axisId, v1, v2); //, sstep);
    115.                                                    //           doReplot = true;
    116.             }
    117.         }
    118.     }
    119. };
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  2. The following user says thank you to ifhmcos for this useful post:

    embeddedmz (29th August 2019)
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