实现滚轮对画布的缩放(以鼠标位置为锚点)

include/designerView.h

@@ -11,8 +11,23 @@ public:
     explicit DesignerView(QWidget *parent = 0);
     virtual ~DesignerView();
 
+protected:
+    virtual void contextMenuEvent(QContextMenuEvent*) override;
+    virtual void mousePressEvent(QMouseEvent*) override;
+    virtual void mouseMoveEvent(QMouseEvent*) override;
+    virtual void mouseReleaseEvent(QMouseEvent*) override;
+    virtual void wheelEvent(QWheelEvent*) override;
+
 private:
     void initialize();
+    //缩放相关
+    void zoom(const QPointF&, double);
+    bool zoomLimit(double&);
+    double getScaleFactor();
+
+private:
+    bool   m_bMousePress;
+    double m_dZoomVaule;
 };
 
 #endif

source/designerScene.cpp

@@ -37,6 +37,11 @@ void DesignerScene::drawBackground(QPainter* painter, const QRectF& rect)
     //补齐最后两条
     painter->drawLine(sceneRect.right(), sceneRect.top(), sceneRect.right(), sceneRect.bottom());
     painter->drawLine(sceneRect.left(), sceneRect.bottom(), sceneRect.right(), sceneRect.bottom());
+
+    //原点
+    // painter->setPen(Qt::red);
+    // painter->setBrush(Qt::red);
+    // painter->drawEllipse(0, 0, 50, 50);
 }
 
 void DesignerScene::mousePressEvent(QGraphicsSceneMouseEvent* mouseEvent)

source/designerView.cpp

@@ -1,8 +1,14 @@
 #include "designerView.h"
+#include <QMouseEvent>
+
+#define MAX_ZoomValue 50.0
+#define MIN_ZoomValue 0.02
 
 DesignerView::DesignerView(QWidget *parent)
     : QGraphicsView(parent)
 {
+    m_bMousePress = false;
+    m_dZoomVaule = 1.0;
     initialize();
 }
 DesignerView::~DesignerView()
@@ -26,3 +32,96 @@ void DesignerView::initialize()
 
     centerOn(0, 0);
 }
+
+bool DesignerView::zoomLimit(double& value)
+{
+    m_dZoomVaule *= value;
+    if(m_dZoomVaule >= MAX_ZoomValue)
+    {
+        m_dZoomVaule = MAX_ZoomValue;
+        value = m_dZoomVaule / getScaleFactor();
+    }
+    else if(m_dZoomVaule <= MIN_ZoomValue)
+    {
+        m_dZoomVaule = MIN_ZoomValue;
+        value = m_dZoomVaule / getScaleFactor();
+    }
+
+    if(qFabs(value - 1) < 0.01) //缩放因子近似为1
+        return true;
+
+    return false;
+}
+
+void DesignerView::zoom(const QPointF& mousePos, double zoomFactor)
+{
+    if(zoomLimit(zoomFactor))
+        return;
+
+    /*
+     * QGraphicsView的默认transformationAnchor(变换锚点)是AnchorViewCenter，也就是中心，此处希望以鼠标指向为变换中心,
+     * AnchorUnderMouse可以实现，但经尝试没有自己进行移动(translate)效果好，所以先设置成NoAnchor,变换后再设置回来
+    */
+    ViewportAnchor lastAnchor = this->transformationAnchor();
+    setTransformationAnchor(QGraphicsView::NoAnchor);
+    QPointF targetScenePos = mapToScene(mousePos.toPoint());
+    QTransform trans = transform();
+    trans.translate(targetScenePos.x(), targetScenePos.y());
+    trans.scale(zoomFactor, zoomFactor);
+    trans.translate(-targetScenePos.x(), -targetScenePos.y());
+    setTransform(trans);
+    setTransformationAnchor(lastAnchor);
+}
+
+double DesignerView::getScaleFactor()
+{
+    //QTransform为一个3*3的矩阵，m11和m22元素分别为水平和垂直的缩放值
+    return this->transform().m11();
+}
+
+void DesignerView::contextMenuEvent(QContextMenuEvent* event)
+{
+    Q_UNUSED(event);
+    m_bMousePress = false;
+}
+
+void DesignerView::mousePressEvent(QMouseEvent* event)
+{
+    if (event->button() == Qt::MiddleButton) //按住中键进行拖动
+    {
+        m_bMousePress = true;
+    }
+    else
+        QGraphicsView::mousePressEvent(event);
+}
+
+void DesignerView::mouseMoveEvent(QMouseEvent* event)
+{
+    if(m_bMousePress)
+    {
+
+    }
+    else
+        QGraphicsView::mouseMoveEvent(event);
+}
+
+void DesignerView::mouseReleaseEvent(QMouseEvent* event)
+{
+    if (event->button() == Qt::MiddleButton) //按住中键进行拖动
+    {
+        m_bMousePress = false;
+    }
+    else
+        QGraphicsView::mouseReleaseEvent(event);
+}
+
+void DesignerView::wheelEvent(QWheelEvent* event) //滚轮进行放大缩小
+{
+    QPointF mousePos = event->position();
+    double angleDeltaY = event->angleDelta().y();
+    double zoomFactor = qPow(1.0015, angleDeltaY); //可以实现更平滑的缩放
+    zoom(mousePos, zoomFactor);
+
+    //注意不要调用基类的滚轮函数，否则滚轮事件会映射到滚动条操作
+    //QGraphicsView::wheelEvent(event);
+}

source/util/scalingSelector.cpp

@@ -1,4 +1,4 @@
-#include "util/ScalingSelector.h"
+#include "util/scalingSelector.h"
 #include <QGraphicsSceneMouseEvent>
 #include <QGraphicsView>
 #include <graphicsItem/graphicsBaseItem.h>