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    <p>Such zooming is a bit tricky. Let me share my own class for doing that.</p> <p>Header:</p> <pre><code>#include &lt;QObject&gt; #include &lt;QGraphicsView&gt; /*! * 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 Graphics_view_zoom : public QObject { Q_OBJECT public: Graphics_view_zoom(QGraphicsView* view); void gentle_zoom(double factor); void set_modifiers(Qt::KeyboardModifiers modifiers); void set_zoom_factor_base(double value); private: QGraphicsView* _view; Qt::KeyboardModifiers _modifiers; double _zoom_factor_base; QPointF target_scene_pos, target_viewport_pos; bool eventFilter(QObject* object, QEvent* event); signals: void zoomed(); }; </code></pre> <p>Source:</p> <pre><code>#include "Graphics_view_zoom.h" #include &lt;QMouseEvent&gt; #include &lt;QApplication&gt; #include &lt;QScrollBar&gt; #include &lt;qmath.h&gt; Graphics_view_zoom::Graphics_view_zoom(QGraphicsView* view) : QObject(view), _view(view) { _view-&gt;viewport()-&gt;installEventFilter(this); _view-&gt;setMouseTracking(true); _modifiers = Qt::ControlModifier; _zoom_factor_base = 1.0015; } void Graphics_view_zoom::gentle_zoom(double factor) { _view-&gt;scale(factor, factor); _view-&gt;centerOn(target_scene_pos); QPointF delta_viewport_pos = target_viewport_pos - QPointF(_view-&gt;viewport()-&gt;width() / 2.0, _view-&gt;viewport()-&gt;height() / 2.0); QPointF viewport_center = _view-&gt;mapFromScene(target_scene_pos) - delta_viewport_pos; _view-&gt;centerOn(_view-&gt;mapToScene(viewport_center.toPoint())); emit zoomed(); } void Graphics_view_zoom::set_modifiers(Qt::KeyboardModifiers modifiers) { _modifiers = modifiers; } void Graphics_view_zoom::set_zoom_factor_base(double value) { _zoom_factor_base = value; } bool Graphics_view_zoom::eventFilter(QObject *object, QEvent *event) { if (event-&gt;type() == QEvent::MouseMove) { QMouseEvent* mouse_event = static_cast&lt;QMouseEvent*&gt;(event); QPointF delta = target_viewport_pos - mouse_event-&gt;pos(); if (qAbs(delta.x()) &gt; 5 || qAbs(delta.y()) &gt; 5) { target_viewport_pos = mouse_event-&gt;pos(); target_scene_pos = _view-&gt;mapToScene(mouse_event-&gt;pos()); } } else if (event-&gt;type() == QEvent::Wheel) { QWheelEvent* wheel_event = static_cast&lt;QWheelEvent*&gt;(event); if (QApplication::keyboardModifiers() == _modifiers) { if (wheel_event-&gt;orientation() == Qt::Vertical) { double angle = wheel_event-&gt;angleDelta().y(); double factor = qPow(_zoom_factor_base, angle); gentle_zoom(factor); return true; } } } Q_UNUSED(object) return false; } </code></pre> <p>Usage example:</p> <pre><code>Graphics_view_zoom* z = new Graphics_view_zoom(ui-&gt;graphicsView); z-&gt;set_modifiers(Qt::NoModifier); </code></pre>
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    1. POQGraphicsView Zooming in and out under mouse position using mouse wheel
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    1. USPavel Strakhov
    1. USPavel Strakhov
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    1. COCheers this works really well, there were some errors that were flagged when i tried to compile it `QMouseEvent* mouse_event = static_cast<QMouseEvent*>(event);` i had to change to `QMouseEvent* mouse_event = (QMouseEvent *) event`; apart from that all working thank you. do you mind explaining what some of the hard coded values are for though so i can understand exactly what its doing and why , thanks again ill accept soon
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    2. COThank you very much @Pavel!
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    3. CODoesn't this recenter the view to where the mouse was pointing rather than zooming into/out of the mouse cursor?
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