效果图

• 在scene上绘制一个图元QGraphicsObject的矩形，可以自由拖动且拖动四个角可以自由变换矩形需要如下处理。

矩形四个角

1. 四个角的点需要独立处理继承于QGraphicsObject,当我们点击时拖动时发送信号给矩形，进行矩形变换。

• 变量

public:/// @brief 点位int pointIndex;/// @brief 偏移位QPointF pressPoint;

RectanglePoint::RectanglePoint(ICanvasScene* canvasScene, int index, QGraphicsItem* parent): QGraphicsObject(parent), pointIndex(index)
{setAcceptHoverEvents(true);
}RectanglePoint::~RectanglePoint() { }QList<RectanglePoint*> RectanglePoint::createRectanglePoints(ICanvasScene* canvasScene, QPolygonF& cachePoints)
{QList<RectanglePoint*> result;if (nullptr == canvasScene) {return result;}for (int i = 0; i < cachePoints.size(); ++i) {RectanglePoint* point = new RectanglePoint(canvasScene, i);if (point) {result.append(point);}}return result;
}QRectF RectanglePoint::boundingRect() const
{return QRectF(-controlSize, -controlSize, controlSize * 2, controlSize * 2);
}void RectanglePoint::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget) { }void RectanglePoint::mousePressEvent(QGraphicsSceneMouseEvent* event)
{if (event->button() != Qt::LeftButton) {return GraphicsLayer::mousePressEvent(event);}event->accept();pressPoint = event->scenePos();emit positionChanged(QPointF(), pointIndex, startedChanged);
}void RectanglePoint::mouseMoveEvent(QGraphicsSceneMouseEvent* event)
{if (!event->buttons().testFlag(Qt::LeftButton)) {return GraphicsLayer::mouseMoveEvent(event);}QPointF startP = pressPoint;QPointF offset = event->scenePos() - startP;event->accept();emit positionChanged(offset, pointIndex, inChanged);
}void RectanglePoint::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{if (event->button() != Qt::LeftButton) {return GraphicsLayer::mouseReleaseEvent(event);}QPointF startP = pressPoint;QPointF offset = event->scenePos() - startP;event->accept();emit positionChanged(offset, pointIndex, finishedChanged);
}

• createRectanglePoints函数是静态函数，矩形生成时会调用，并传入四个点位。
• positionChanged的第三个参数为当前操作的状态的枚举（鼠标点击，移动与释放）

矩形

• 变量

private:/// @brief 当前矩形大小QRectF mboundingRect;/// @brief 矩形的四个点QPolygonF cachePoints;/// @brief 变换的点位QPolygonF startChangePoints;/// @brief 四个角的类QList<RectanglePoint*> rectanglePoints;

const qreal controlSize = 5.0;
GisGridCustomRectItem::GisGridCustomRectItem(QRectF boundingRect, ICanvasScene* canvasScene, QGraphicsItem* parent): QGraphicsObject(parent),mboundingRect(boundingRect)
{setFlags(QGraphicsObject::ItemIsMovable | QGraphicsObject::ItemIsSelectable| QGraphicsObject::ItemSendsGeometryChanges); // 允许移动cachePoints << boundingRect.topLeft() << boundingRect.topRight() << boundingRect.bottomRight()<< boundingRect.bottomLeft();rectanglePoints = RectanglePoint::createRectanglePoints(canvasScene, cachePoints);QListIterator<RectanglePoint*> RectanglePointIter(rectanglePoints);while (RectanglePointIter.hasNext()) {RectanglePoint* RectanglePointGraph = RectanglePointIter.next();if (RectanglePointGraph) {RectanglePointGraph->setParentItem(this);connect(RectanglePointGraph, &RectanglePoint::positionChanged, this,&GisGridCustomRectItem::onRectPositionChange);RectanglePointGraph->setZValue(RectanglePointGraph->zValue() + 1);}}refreshPointPoistion();
}GisGridCustomRectItem::~GisGridCustomRectItem() { }void GisGridCustomRectItem::paint(QPainter* painter, const QStyleOptionGraphicsItem*, QWidget*)
{painter->save();QPen pen;painter->setBrush(QColor(230, 230, 230, 100));if (isSelected()) {pen.setColor(QColor(0x2E9FE6));}painter->setPen(pen);QPainterPath path;path.addPolygon(cachePoints);path.closeSubpath();painter->drawPath(path);if (isSelected()) {drawPointsRect(painter);}painter->restore();
}QRectF GisGridCustomRectItem::boundingRect() const
{return mboundingRect;return shape().controlPointRect();
}QPainterPath GisGridCustomRectItem::shape() const
{return QGraphicsObject::shape();QPainterPath path;path.addPolygon(cachePoints);path.closeSubpath();QPainterPathStroker stroker;stroker.setWidth(15);path = stroker.createStroke(path);return path;
}QVariant GisGridCustomRectItem::itemChange(GraphicsItemChange change, const QVariant& value)
{// if (change == QGraphicsItem::ItemPositionChange && scene()) {//     return Utility::pointAlignmentToGrid(value.toPointF(), 10);// }return QGraphicsObject::itemChange(change, value);
}void GisGridCustomRectItem::drawPointsRect(QPainter* painter)
{double arrowLength = 7; // 箭头长度// 四个角落上的箭头，一个角绘制两条箭头构成一个双向箭头// 计算45度角（PI/4 弧度）和225度角（5*PI/4 弧度）double angle45 = M_PI / 4;double angle225 = 5 * M_PI / 4;// 左上角的双向箭头drawSingleArrow(painter, cachePoints[0], angle45, arrowLength);  // 对角向右下drawSingleArrow(painter, cachePoints[0], angle225, arrowLength); // 对角向左上// 右上角的双向箭头drawSingleArrow(painter, cachePoints[3], -angle45, arrowLength);       // 对角向左下drawSingleArrow(painter, cachePoints[3], M_PI - angle45, arrowLength); // 对角向右上// 左下角的双向箭头drawSingleArrow(painter, cachePoints[1], M_PI - angle45, arrowLength); // 对角向左下drawSingleArrow(painter, cachePoints[1], -angle45, arrowLength);       // 对角向右上// 右下角的双向箭头drawSingleArrow(painter, cachePoints[2], angle225 - M_PI, arrowLength); // 对角向右上drawSingleArrow(painter, cachePoints[2], angle225, arrowLength);        // 对角向左下
}void GisGridCustomRectItem::onRectPositionChange(QPointF delta, int index, itemRectChange state)
{ICanvasScene* canvasScene = getCanvasScene();if (!canvasScene) {return;}ICanvasView* canvasView = canvasScene->getCanvasView();if (!canvasView) {return;}auto interactioMode = (InteractionMode)canvasView->getInteractionMode();if (interactioMode == kAreaAmplification) {return;}switch (state) {case startedChanged:startChangePoints = cachePoints;break;case inChanged:changeCachePoints(delta, index);break;case finishedChanged:changeCachePoints(delta, index);refreshPointPoistion();default:break;}update();
}void GisGridCustomRectItem::changeCachePoints(QPointF delta, int index)
{QPolygonF pointF;cachePoints[index] = startChangePoints[index] + delta;if (index == 1 || index == 3) {pointF << cachePoints[1] << cachePoints[3];} else {pointF << cachePoints[0] << cachePoints[2];}QPointF p1 = pointF[0];QPointF p2 = pointF[1];QPointF p3(p2.x(), p1.y());QPointF p4(p1.x(), p2.y());pointF.clear();if (index == 1 || index == 3) {pointF << p3 << p1 << p4 << p2;} else {pointF << p1 << p3 << p2 << p4;}cachePoints = pointF;// 更新矩形大小double minX = std::min({ p1.x(), p2.x(), p3.x(), p4.x() });double minY = std::min({ p1.y(), p2.y(), p3.y(), p4.y() });double maxX = std::max({ p1.x(), p2.x(), p3.x(), p4.x() });double maxY = std::max({ p1.y(), p2.y(), p3.y(), p4.y() });QRectF rect(minX, minY, maxX - minX, maxY - minY);mboundingRect = rect;
}void GisGridCustomRectItem::drawSingleArrow(QPainter* painter, QPointF basePoint, double angle, double length)
{// 计算箭头的末端点QPointF endPoint(basePoint.x() + length * qCos(angle), basePoint.y() + length * qSin(angle));// 绘制箭头的主线painter->drawLine(basePoint, endPoint);// 绘制箭头的两个小边，构成箭头尖端double arrowHeadAngle = M_PI / 5; // 箭头头部的夹角double arrowHeadLength = 5;       // 箭头头部长度QPointF arrowLeft(endPoint.x() - arrowHeadLength * qCos(angle - arrowHeadAngle),endPoint.y() - arrowHeadLength * qSin(angle - arrowHeadAngle));QPointF arrowRight(endPoint.x() - arrowHeadLength * qCos(angle + arrowHeadAngle),endPoint.y() - arrowHeadLength * qSin(angle + arrowHeadAngle));painter->drawLine(endPoint, arrowLeft);painter->drawLine(endPoint, arrowRight);
}void GisGridCustomRectItem::refreshPointPoistion()
{QListIterator<RectanglePoint*> rectanglePointsIter(rectanglePoints);while (rectanglePointsIter.hasNext()) {RectanglePoint* ponit = rectanglePointsIter.next();if (ponit) {ponit->setPos(cachePoints[ponit->pointIndex]);}}
}

• 四个角的双向箭头挺难画的，可以直接画一个简单的圆形就行。
• 对于移动操作而言，应该设置ItemSendsGeometryChanges标志，这允许项目在几何变化时（如位置改变）发送通知。如果没有设置这个标志，项目在移动时将不会调用itemChange函数。
• 拖动矩形有俩种处理形式(看shape于boundingRect函数)
  1. 点击边框拖动，这个需要计算shape路径函数，得到矩形的边框。
  2. 点击矩形内部拖动，这个需要再每次变换后更新一下矩形。
• 矩形的变换关键在于changeCachePoints函数中的处理，其实一个矩形只需要俩个点，另外俩个点根据这俩个点变换，不然你拖动起来可能不是一个矩形了。