小练习10 图片效果(放大、旋转 扭曲、坐标保存)

工程代码：  11_pic.rar  





1. 实现图片的放大

void Dialog::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    QPixmap pix;
    pix.load("linux.jpg");
    painter.drawPixmap(0,0,100,100,pix);

    qreal width = pix.width(); //获得以前图片的大小
    qreal height = pix.height();

    //将图片的宽和高都扩大两倍，并且在给定的矩形保持宽高的比值
    /*IgnoreAspectRatio, 不保持图片的长宽比
        KeepAspectRatio, 给定的矩形中保持长宽比
        KeepAspectRatioByExpanding 保持长宽比，但可能超出给定的矩形
*/
    pix = pix.scaled(width*2,height*2,Qt::KeepAspectRatio);
    painter.drawPixmap(100,100,pix);
}

2. 图片的旋转

void Dialog::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    QPixmap pix;
    pix.load("linux.jpg");
    painter.translate(50,50);//使坐标原点在(50,50)
    painter.rotate(90);//以新的原点坐标，顺时针旋转90度
    painter.translate(-50,-50);//恢复原点在(0,0)
    painter.drawPixmap(0,0,100,100,pix);
}

3.图片扭曲

void Dialog::paintEvent(QPaintEvent *)
{

    /*图片扭曲*/
    QPainter painter(this);
    QPixmap pix;
    pix.load("linux.jpg");
    painter.drawPixmap(0,0,100,100,pix);

    painter.shear(0.5,0);//横向扭曲
    painter.drawPixmap(100,0,100,100,pix);

    painter.shear(0,0.5);//纵向扭曲
    painter.drawPixmap(0,100,100,100,pix);

    painter.shear(0.5,0.5);//横向扭曲
    painter.drawPixmap(100,100,100,100,pix);
}

4.坐标的保存

void Dialog::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.save(); //保存坐标系状态
    painter.translate(100,100);
    painter.drawLine(0,0,50,50);

    painter.restore(); //恢复以前的坐标系状态
    painter.drawLine(0,0,50,50);
}