Qt 坐标變換

1.坐标變換常用接口

void translate(qreal dx,qreal dy)	平移
void rotate(qreal angle)	旋轉
void scale(qreal sx,qreal sy)	縮放
void save	儲存painter目前的狀态
void restore()	恢複上一次狀态
void resetTransform()	複位所有的坐标變換

2.示例

畫五角星

void Widget::paintEvent(QPaintEvent *event)
{
    //建立QPainter對象，指明父對象，否則不能看見
    QPainter painter(this);

    //先畫一條線
    QPen pen;

    //設定線寬
    pen.setWidth(2);

    //設定顔色
    pen.setColor(Qt::red);

    //設定線的樣式 實線、虛線
    pen.setStyle(Qt::SolidLine);

    //設定線端點樣式
    pen.setCapStyle(Qt::FlatCap);

    pen.setJoinStyle(Qt::BevelJoin);

    //設定畫筆
    painter.setPen(pen);

    //半徑
    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))
    };

    //設定字型
    QFont font;
    font.setPixelSize(12);
    font.setBold(true);
    painter.setFont(font);

    //設定畫刷
    QBrush brush;

    //畫刷設定顔色
    brush.setColor(Qt::yellow);

    //設定填充樣式
    brush.setStyle(Qt::SolidPattern);

    //設定畫刷
    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]);

    //閉合路徑，最後一個點與第一個點相連
    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");

    //保持坐标狀态
    painter.save();

    //平移
    painter.translate(100,120);

    //畫星星
    painter.drawPath(painterPath);

    painter.drawText(0,0,"S1");

    //恢複坐标狀态
    painter.restore();

    //平移
    painter.translate(300,120);
    //縮放
    painter.scale(0.8,0.8);
    //順時針旋轉90
    painter.rotate(90);
    painter.drawPath(painterPath);
    painter.drawText(0,0,"S2");

    //複位所有坐标變換
    painter.resetTransform();
    //平移
    painter.translate(500,120);
    //逆時針旋轉145
    painter.rotate(-145);

    painter.drawPath(painterPath);
    painter.drawText(0,0,"S3");
}