Qt学习10:像丝一样滑(双缓冲)

 

void CannonField::paintEvent(QPaintEvent *e)
{
	// -------------------------------------
	// QPaintEvent包含一个必须被刷新的窗口部件的区域
    // QPainter默认只能在paintEvent里面调用
	// -------------------------------------
	QRect cr = cannonRect();

	// --------------------------------------
	// 只要有一个象素相交，就返回true。
	// --------------------------------------
	if (!e->rect().intersects(cr))
	{
        return;
	}

	QPixmap pix(cr.size());
	//用this的背景色填充The QPoint offset 
	//defines a point in widget coordinates 
	//to which the pixmap's top-left pixel will be mapped to.
	pix.fill(this, cr.topLeft());

	//先绘到QPixmap上，再把QPixmap贴到this.
	QPainter p(&pix);

	//图片设为蓝色
	p.setBrush(Qt::blue);
	p.setPen(Qt::PenStyle::NoPen);

	//这个移的是坐标系,相当于QRect在做所有的运算时，
	//都先要offerset(-0, -pix.height()   
	p.translate(0, pix.height());

	p.drawPie(QRect(-35, -35, 70, 70), 0, 90*16);

	//rotate是旋轩坐标系.顺时针方向为正，逆时针为负.
	p.rotate(-ang);
	p.drawRect(QRect(33, -8, 15, 8));
	//Ends painting. Any resources used while painting are released. 
	p.end();

	//only one painter at a time
	p.begin(this);
	p.drawPixmap(cr.topLeft(), pix);
}

右下角绘制:

void CannonField::paintEvent(QPaintEvent *e)
{
	// -------------------------------------
	// QPaintEvent包含一个必须被刷新的窗口部件的区域
    // QPainter默认只能在paintEvent里面调用
	// -------------------------------------
	QRect cr = cannonRect();

	// --------------------------------------
	// 只要有一个象素相交，就返回true。
	// --------------------------------------
	if (!e->rect().intersects(cr))
	{
        return;
	}

	QPixmap pix(cr.size());
	//用this的背景色填充The QPoint offset 
	//defines a point in widget coordinates 
	//to which the pixmap's top-left pixel will be mapped to.
	pix.fill(this, cr.topLeft());

	//先绘到QPixmap上，再把QPixmap贴到this.
	QPainter p(&pix);

	//图片设为蓝色
	p.setBrush(Qt::blue);
	p.setPen(Qt::PenStyle::NoPen);

	//这个移的是坐标系,相当于QRect在做所有的运算时，
	//都先要offerset(-0, -pix.height()   
	//p.translate(0, pix.height());

	//p.drawPie(QRect(-35, -35, 70, 70), 0, 90*16);
	p.translate(pix.width(), pix.height());
	p.drawPie(QRect(-35, -35, 70, 70), 90*16, 90*16);
	//p.drawRect(QRect(-35, -35, 70, 70));

	//rotate是旋轩坐标系.顺时针方向为正，逆时针为负.
	p.rotate(ang);
	p.drawRect(QRect(-33-15, -8, 15, 8));
	//Ends painting. Any resources used while painting are released. 
	p.end();

	//only one painter at a time
	p.begin(this);
	p.drawPixmap(cr.topLeft(), pix);
}

1.先画到临时的pix上，再一次绘出来，双缓冲

2.drawPie的起始角度不要忘了*16，还有它是以逆时针旋转算角度的