New mechanizm zooming QGraphicsView using mouse wheel.

--HG--
branch : develop

src/app/widgets/vmaingraphicsview.cpp

@@ -34,100 +34,63 @@
 #include <QScrollBar>
 #include "../tools/vabstracttool.h"
 
+#include <QMouseEvent>
+#include <qmath.h>
+
 //---------------------------------------------------------------------------------------------------------------------
-/**
- * @brief VMainGraphicsView constructor.
- * @param parent parent object.
- */
-VMainGraphicsView::VMainGraphicsView(QWidget *parent)
-    :QGraphicsView(parent), _numScheduledScalings(0)
+GraphicsViewZoom::GraphicsViewZoom(QGraphicsView* view)
+  : QObject(view), _view(view), _numScheduledScalings(0)
 {
-    this->setResizeAnchor(QGraphicsView::AnchorUnderMouse);
-    this->setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
-    this->setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
-    this->setInteractive(true);
+  _view->viewport()->installEventFilter(this);
+  _view->setMouseTracking(true);
+  _modifiers = Qt::ControlModifier;
+  _zoom_factor_base = 1.0015;
 }
 
 //---------------------------------------------------------------------------------------------------------------------
-/**
- * @brief wheelEvent handle wheel events.
- * @param event wheel event.
- */
-//cppcheck-suppress unusedFunction
-void VMainGraphicsView::wheelEvent(QWheelEvent *event)
+void GraphicsViewZoom::gentle_zoom(double factor)
 {
-    int numSteps = event->delta() / 8 / 15;  // see QWheelEvent documentation
-
-    _numScheduledScalings += numSteps;
-    if (_numScheduledScalings * numSteps < 0)
-    {  // if user moved the wheel in another direction, we reset
-        _numScheduledScalings = numSteps;       // previously scheduled scalings
-    }
-
-    QTimeLine *anim = new QTimeLine(300, this);
-    anim->setUpdateInterval(20);
-
-    if (QApplication::keyboardModifiers() == Qt::ControlModifier)
-    {// If you press CTRL this code will be executed
-        connect(anim, &QTimeLine::valueChanged, this, &VMainGraphicsView::scalingTime);
-    }
-    else
-    {
-        connect(anim, &QTimeLine::valueChanged, this, &VMainGraphicsView::scrollingTime);
-    }
-    connect(anim, &QTimeLine::finished, this, &VMainGraphicsView::animFinished);
-    anim->start();
+  _view->scale(factor, factor);
+  _view->centerOn(target_scene_pos);
+  QPointF delta_viewport_pos = target_viewport_pos - QPointF(_view->viewport()->width() / 2.0,
+                                                             _view->viewport()->height() / 2.0);
+  QPointF viewport_center = _view->mapFromScene(target_scene_pos) - delta_viewport_pos;
+  _view->centerOn(_view->mapToScene(viewport_center.toPoint()));
+  emit zoomed();
 }
 
 //---------------------------------------------------------------------------------------------------------------------
-/**
- * @brief scalingTime call each time when need handle scaling.
- * @param x value from 0.0 to 1.0
- */
-void VMainGraphicsView::scalingTime(qreal x)
+void GraphicsViewZoom::set_modifiers(Qt::KeyboardModifiers modifiers)
 {
-    Q_UNUSED(x);
-    const QPointF p0scene = mapToScene(mapFromGlobal(QCursor::pos()));
+  _modifiers = modifiers;
 
-    qreal factor = 1.0 + static_cast<qreal>(_numScheduledScalings) / 50.0;
-    scale(factor, factor);
-
-    const QPointF p1mouse = mapFromScene(p0scene);
-    const QPointF move = p1mouse - this->mapFromGlobal(QCursor::pos()); // The move
-    horizontalScrollBar()->setValue(static_cast<qint32>(move.x()) + horizontalScrollBar()->value());
-    verticalScrollBar()->setValue(static_cast<qint32>(move.y()) + verticalScrollBar()->value());
-
-    VAbstractTool::NewSceneRect(this->scene(), this);
-
-    emit NewFactor(factor);
 }
 
 //---------------------------------------------------------------------------------------------------------------------
-/**
- * @brief scrollingTime call each time when need handle scrolling.
- * @param x value from 0.0 to 1.0
- */
-void VMainGraphicsView::scrollingTime(qreal x)
+void GraphicsViewZoom::set_zoom_factor_base(double value)
+{
+    _zoom_factor_base = value;
+}
+
+//---------------------------------------------------------------------------------------------------------------------
+void GraphicsViewZoom::scrollingTime(qreal x)
 {
     Q_UNUSED(x);
     qreal factor = 1.0;
     if (_numScheduledScalings < 0)
     {
-        verticalScrollBar()->setValue(qRound(verticalScrollBar()->value() + factor*3.5));
-        emit NewFactor(factor);
+        factor = factor*2.8;
     }
     else
     {
-        verticalScrollBar()->setValue(qRound(verticalScrollBar()->value() - factor*3.5));
-        emit NewFactor(factor);
+        factor = factor*-2.8;
     }
+
+    _view->verticalScrollBar()->setValue(qRound(_view->verticalScrollBar()->value() + factor));
 }
 
 //---------------------------------------------------------------------------------------------------------------------
-/**
- * @brief animFinished
- */
-void VMainGraphicsView::animFinished()
+void GraphicsViewZoom::animFinished()
 {
     if (_numScheduledScalings > 0)
     {
@@ -140,6 +103,69 @@ void VMainGraphicsView::animFinished()
     sender()->~QObject();
 }
 
+//---------------------------------------------------------------------------------------------------------------------
+bool GraphicsViewZoom::eventFilter(QObject *object, QEvent *event)
+{
+  if (event->type() == QEvent::MouseMove)
+  {
+    QMouseEvent* mouse_event = static_cast<QMouseEvent*>(event);
+    QPointF delta = target_viewport_pos - mouse_event->pos();
+    if (qAbs(delta.x()) > 5 || qAbs(delta.y()) > 5)
+    {
+      target_viewport_pos = mouse_event->pos();
+      target_scene_pos = _view->mapToScene(mouse_event->pos());
+    }
+  }
+  else if (event->type() == QEvent::Wheel)
+  {
+    QWheelEvent* wheel_event = static_cast<QWheelEvent*>(event);
+    if (QApplication::keyboardModifiers() == _modifiers)
+    {
+      if (wheel_event->orientation() == Qt::Vertical)
+      {
+        double angle = wheel_event->angleDelta().y();
+        double factor = qPow(_zoom_factor_base, angle);
+        gentle_zoom(factor);
+        return true;
+      }
+    }
+    else
+    {
+        int numSteps = wheel_event->delta() / 8 / 15;  // see QWheelEvent documentation
+
+        _numScheduledScalings += numSteps;
+        if (_numScheduledScalings * numSteps < 0)
+        {  // if user moved the wheel in another direction, we reset
+            _numScheduledScalings = numSteps;       // previously scheduled scalings
+        }
+
+        QTimeLine *anim = new QTimeLine(300, this);
+        anim->setUpdateInterval(20);
+        connect(anim, &QTimeLine::valueChanged, this, &GraphicsViewZoom::scrollingTime);
+        connect(anim, &QTimeLine::finished, this, &GraphicsViewZoom::animFinished);
+        anim->start();
+        return true;
+    }
+  }
+  Q_UNUSED(object)
+  return false;
+}
+
+//---------------------------------------------------------------------------------------------------------------------
+/**
+ * @brief VMainGraphicsView constructor.
+ * @param parent parent object.
+ */
+VMainGraphicsView::VMainGraphicsView(QWidget *parent)
+    :QGraphicsView(parent), zoom(nullptr)
+{
+    zoom = new GraphicsViewZoom(this);
+    this->setResizeAnchor(QGraphicsView::AnchorUnderMouse);
+    this->setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
+    this->setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
+    this->setInteractive(true);
+}
+
 //---------------------------------------------------------------------------------------------------------------------
 void VMainGraphicsView::ZoomIn()
 {

src/app/widgets/vmaingraphicsview.h

@@ -29,8 +29,65 @@
 #ifndef VMAINGRAPHICSVIEW_H
 #define VMAINGRAPHICSVIEW_H
 
+#include <QObject>
 #include <QGraphicsView>
 
+/*!
+ * This class adds ability to zoom QGraphicsView using mouse wheel. The point under cursor
+ * remains motionless while it's possible.
+ *
+ * Note that it becomes not possible when the scene's
+ * size is not large enough comparing to the viewport size. QGraphicsView centers the picture
+ * when it's smaller than the view. And QGraphicsView's scrolls boundaries don't allow to
+ * put any picture point at any viewport position.
+ *
+ * When the user starts scrolling, this class remembers original scene position and
+ * keeps it until scrolling is completed. It's better than getting original scene position at
+ * each scrolling step because that approach leads to position errors due to before-mentioned
+ * positioning restrictions.
+ *
+ * When zommed using scroll, this class emits zoomed() signal.
+ *
+ * Usage:
+ *
+ *   new Graphics_view_zoom(view);
+ *
+ * The object will be deleted automatically when the view is deleted.
+ *
+ * You can set keyboard modifiers used for zooming using set_modified(). Zooming will be
+ * performed only on exact match of modifiers combination. The default modifier is Ctrl.
+ *
+ * You can change zoom velocity by calling set_zoom_factor_base().
+ * Zoom coefficient is calculated as zoom_factor_base^angle_delta
+ * (see QWheelEvent::angleDelta).
+ * The default zoom factor base is 1.0015.
+ */
+class GraphicsViewZoom : public QObject
+{
+    Q_OBJECT
+public:
+    GraphicsViewZoom(QGraphicsView* view);
+    void gentle_zoom(double factor);
+    void set_modifiers(Qt::KeyboardModifiers modifiers);
+    void set_zoom_factor_base(double value);
+signals:
+    void zoomed();
+public slots:
+    void scrollingTime(qreal x);
+    void animFinished();
+private:
+    QGraphicsView*        _view;
+    Qt::KeyboardModifiers _modifiers;
+    double                _zoom_factor_base;
+    QPointF                target_scene_pos;
+    QPointF               target_viewport_pos;
+
+    bool eventFilter(QObject* object, QEvent* event);
+private:
+    /** @brief _numScheduledScalings keep number scheduled scalings. */
+    qint32   _numScheduledScalings;
+};
+
 /**
  * @brief The VMainGraphicsView class main scene view.
  */
@@ -53,20 +110,15 @@ signals:
      */
     void         MouseRelease();
 public slots:
-    void     scalingTime(qreal x);
-    void     scrollingTime(qreal x);
-    void     animFinished();
     void     ZoomIn();
     void     ZoomOut();
     void     ZoomOriginal();
     void     ZoomFitBest();
 protected:
-    void     wheelEvent ( QWheelEvent * event );
     void     mousePressEvent(QMouseEvent *mousePress);
     void     mouseReleaseEvent(QMouseEvent *event);
 private:
-    /** @brief _numScheduledScalings keep number scheduled scalings. */
-    qint32   _numScheduledScalings;
+    GraphicsViewZoom* zoom;
 };
 
 #endif // VMAINGRAPHICSVIEW_H