QT在控件graphicsView中绘制箭头

前言：

对之前箭头没有成功绘制的补充，因为没有直接的箭头项，所以需要自己进行绘制

基础夯实：

可以直接看，建议看一下之前的绘制过程
在控件graphicsView中实现绘图功能（一）
在控件graphicsView中实现绘图功能（二）
在控件graphicsView中实现绘图功能（三）

成功效果展示：

失败效果展示：

核心代码：

#include "CustomGraphicsView.h"
#include 
#include 
#include 
#include 
#include 

CustomGraphicsView::CustomGraphicsView(QWidget *parent)
    : QGraphicsView(parent), isDrawing(false), arrowPolygonItem(nullptr),arrowLineItem(nullptr)
{
    const double arrowSize = 10.0;
}

void CustomGraphicsView::setDrawMode(DrawMode mode)
{
    currentDrawMode = mode;
}

void CustomGraphicsView::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton) {
        isDrawing = true;
        startPoint = mapToScene(event->pos());
        endPoint = startPoint; // Initialize endPoint to startPoint

        switch (currentDrawMode) {
        case ArrowsMode:
            arrowPolygonItem = nullptr;
            arrowLineItem = nullptr; // 重置箭头直线项
            break;
        default:
            break;
        }
        emit mouseClicked(event->pos());
    }

    QGraphicsView::mousePressEvent(event);
}

void CustomGraphicsView::mouseMoveEvent(QMouseEvent *event)
{
    if (isDrawing) {
        endPoint = mapToScene(event->pos());

        switch (currentDrawMode) {
        case ArrowsMode: {
            // 绘制直线
            if (!arrowLineItem) {
                arrowLineItem = scene()->addLine(QLineF(startPoint, endPoint), QPen(Qt::green));
            } else {
                arrowLineItem->setLine(QLineF(startPoint, endPoint));
            }

            // 绘制箭头头部
            if (!arrowPolygonItem) {
                // 计算从起点到终点的角度
                double angle = std::atan2(endPoint.y() - startPoint.y(), endPoint.x() - startPoint.x());

                // 调整角度，确保箭头是锐角（15度）
                double arrowAngle = M_PI - 15.0 / 180.0 * M_PI; // 15度角

                // 计算箭头的三个顶点
                QPointF arrowP1 = QPointF(endPoint.x() + 10.0 * std::cos(angle + arrowAngle), endPoint.y() + 10.0 * std::sin(angle + arrowAngle));
                QPointF arrowP2 = endPoint;
                QPointF arrowP3 = QPointF(endPoint.x() + 10.0 * std::cos(angle - arrowAngle), endPoint.y() + 10.0 * std::sin(angle - arrowAngle));

                QPolygonF arrowHeadPolygon;
                arrowHeadPolygon << arrowP1 << arrowP2 << arrowP3;
                arrowPolygonItem = scene()->addPolygon(arrowHeadPolygon, QPen(Qt::green), QBrush(Qt::green));
            } else {
                double angle = std::atan2(endPoint.y() - startPoint.y(), endPoint.x() - startPoint.x());
                double arrowAngle = M_PI - 15.0 / 180.0 * M_PI; // 15度角

                QPointF arrowP1 = QPointF(endPoint.x() + 10.0 * std::cos(angle + arrowAngle), endPoint.y() + 10.0 * std::sin(angle + arrowAngle));
                QPointF arrowP2 = endPoint;
                QPointF arrowP3 = QPointF(endPoint.x() + 10.0 * std::cos(angle - arrowAngle), endPoint.y() + 10.0 * std::sin(angle - arrowAngle));
                QPolygonF arrowHeadPolygon;
                arrowHeadPolygon << arrowP1 << arrowP2 << arrowP3;
                arrowPolygonItem->setPolygon(arrowHeadPolygon);
            }
            break;
        }
        default:
            break;
        }
    }
    emit mouseMoved(event->pos());
}

void CustomGraphicsView::mouseReleaseEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton && isDrawing) {
        isDrawing = false;
    }

    emit mouseReleased(event->pos());

    QGraphicsView::mouseReleaseEvent(event);
}