一 概述本文章实现了如何在jpeg图片上画多边形。现实中的应用场景有1.在安防监控中IPC摄像头可以设置多个防区用于监测指定区域的状况防区一般都是一个闭合的多边形2.在物体监测时识别到指定物体时会使用矩形将物体框起来。二 代码实现#include widget.h #define WIDTH 1920 #define HEIGHT 1080 void DrawPolygonOnImage(QImage img, const QRect rect, const QPolygon polygon, QPen pen, QBrush brush) { // 空图/空多边形直接返回 if (img.isNull() || polygon.isEmpty()) return; QPainter painter(img); // 抗锯齿优化 painter.setRenderHint(QPainter::Antialiasing, true); // 设置画笔与填充 painter.setPen(pen); painter.setBrush(brush); // 可选限制绘制范围在rect内坐标裁剪 painter.setClipRect(rect); // 绘制闭合多边形 painter.drawPolygon(polygon); painter.end(); } Widget::Widget(QWidget *parent) : QWidget(parent) { setMinimumSize(800,600); #if 0 m_pImage new QImage(WIDTH,HEIGHT,QImage::Format_RGB888); m_pImage-fill(Qt::lightGray); #else m_pImage new QImage(D:/Test/TestDrawPolygon/1.jpeg); #endif QRect rect QRect(0,0,WIDTH,HEIGHT); QPolygon poly; poly QPoint(100, 100) QPoint(300, 120) QPoint(280, 350) QPoint(120, 320); DrawPolygonOnImage(*m_pImage, rect, poly, QPen(Qt::blue, 2), QBrush(QColor(255,255,255, 0))); poly.clear(); poly QPoint(800, 100) QPoint(1100, 120) QPoint(1480, 850) QPoint(920, 1020); DrawPolygonOnImage(*m_pImage, rect, poly, QPen(Qt::blue, 2), QBrush(QColor(255,255,255, 0))); } Widget::~Widget() { } void Widget::drawImg(QPainter *painter, QImage img) { painter-save(); int offset borderWidth * 1 0; if (fillImage) { QRect rect(4,4,width()-8,height()-8); painter-drawImage(rect,img); } else { //按照比例自动居中绘制 m_scaleImage img.scaled(width() - 8, height() - 8, Qt::IgnoreAspectRatio,Qt::SmoothTransformation); #if 0 int pixX rect().center().x() - img.width() / 2; int pixY rect().center().y() - img.height() / 2; QPoint point(pixX, pixY); #endif QRect rect(4,4,width() - 8, height() - 8); painter-drawImage(rect, m_scaleImage); } painter-restore(); } void Widget::paintEvent(QPaintEvent *event) { QPainterPath path; path.setFillRule(Qt::OddEvenFill); path.addRect(0, 0, this-width(), this-height()); //使用全局的 painter brush painter.begin(this); painter.setRenderHints(QPainter::Antialiasing); painter.fillPath(path,brush); if(m_pImage){ drawImg(painter,*m_pImage); } painter.end(); }三 关键函数void DrawPolygonOnImage(QImage img, const QRect rect, const QPolygon polygon, QPen pen, QBrush brush) { // 空图/空多边形直接返回 if (img.isNull() || polygon.isEmpty()) return; QPainter painter(img); // 抗锯齿优化 painter.setRenderHint(QPainter::Antialiasing, true); // 设置画笔与填充 painter.setPen(pen); painter.setBrush(brush); // 可选限制绘制范围在rect内坐标裁剪 painter.setClipRect(rect); // 绘制闭合多边形 painter.drawPolygon(polygon); painter.end(); }四 运行效果