Qt 坐标变换

痛定思痛。 2022-11-06 08:53 140阅读 0赞

# 1.坐标变换常用接口 #

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td>void translate(qreal dx,qreal dy)</td> 
   <td>平移</td> 
  </tr> 
  <tr> 
   <td>void rotate(qreal angle)</td> 
   <td>旋转</td> 
  </tr> 
  <tr> 
   <td>void scale(qreal sx,qreal sy)</td> 
   <td>缩放</td> 
  </tr> 
  <tr> 
   <td>void save</td> 
   <td>保存painter当前的状态</td> 
  </tr> 
  <tr> 
   <td>void restore()</td> 
   <td>恢复上一次状态</td> 
  </tr> 
  <tr> 
   <td>void resetTransform()</td> 
   <td>复位所有的坐标变换</td> 
  </tr> 
 </tbody> 
</table>

# 2.示例 #

画五角星

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3d6ejk1MzIwMDQ2Mw_size_16_color_FFFFFF_t_70][]

void Widget::paintEvent(QPaintEvent *event)
    {
        //创建QPainter对象，指明父对象，否则不能看见
        QPainter painter(this);
    
        //先画一条线
        QPen pen;
    
        //设置线宽
        pen.setWidth(2);
    
        //设置颜色
        pen.setColor(Qt::red);
    
        //设置线的样式 实线、虚线
        pen.setStyle(Qt::SolidLine);
    
        //设置线端点样式
        pen.setCapStyle(Qt::FlatCap);
    
        pen.setJoinStyle(Qt::BevelJoin);
    
        //设置画笔
        painter.setPen(pen);
    
        //半径
        qreal R = 100;
        qreal pi = 3.14159;
        qreal deg = pi*72/180;
    
        QPoint points[5] = {
            QPoint(R,0),
            QPoint(R*std::cos(deg),-R*std::sin(deg)),
            QPoint(R*std::cos(2*deg),-R*std::sin(2*deg)),
            QPoint(R*std::cos(3*deg),-R*std::sin(3*deg)),
            QPoint(R*std::cos(4*deg),-R*std::sin(4*deg))
        };
    
        //设置字体
        QFont font;
        font.setPixelSize(12);
        font.setBold(true);
        painter.setFont(font);
    
        //设置画刷
        QBrush brush;
    
        //画刷设置颜色
        brush.setColor(Qt::yellow);
    
        //设置填充样式
        brush.setStyle(Qt::SolidPattern);
    
        //设置画刷
        painter.setBrush(brush);
    
        QPainterPath painterPath;
        painterPath.moveTo(points[0]);
        painterPath.lineTo(points[2]);
        painterPath.lineTo(points[4]);
        painterPath.lineTo(points[1]);
        painterPath.lineTo(points[3]);
    
        //闭合路径，最后一个点与第一个点相连
        painterPath.closeSubpath();
    
        painterPath.addText(points[0],font,"0");
        painterPath.addText(points[1],font,"1");
        painterPath.addText(points[2],font,"2");
        painterPath.addText(points[3],font,"3");
        painterPath.addText(points[4],font,"4");
    
        //保持坐标状态
        painter.save();
    
        //平移
        painter.translate(100,120);
    
        //画星星
        painter.drawPath(painterPath);
    
        painter.drawText(0,0,"S1");
    
        //恢复坐标状态
        painter.restore();
    
        //平移
        painter.translate(300,120);
        //缩放
        painter.scale(0.8,0.8);
        //顺时针旋转90
        painter.rotate(90);
        painter.drawPath(painterPath);
        painter.drawText(0,0,"S2");
    
        //复位所有坐标变换
        painter.resetTransform();
        //平移
        painter.translate(500,120);
        //逆时针旋转145
        painter.rotate(-145);
    
        painter.drawPath(painterPath);
        painter.drawText(0,0,"S3");
    }

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