我面临着必须擦除 Qt 小部件上先前绘制的区域的问题。
基本思想是,用户通过单击并拖动鼠标来选择屏幕的一个区域,并在所选区域上绘制一个矩形。
标题
class ClearBack : public QWidget
{
Q_OBJECT
public:
explicit ClearBack(const QPoint &startingPos);
bool eventFilter(QObject *obj, QEvent *event);
void paintEvent(QPaintEvent *);
void mouseMoveEvent(QMouseEvent *event);
signals:
void regionSelected(const QRect &);
private:
QRect currentRegion;
};
实施
ClearBack::ClearBack(const QPoint &startingPos)
{
setBackgroundRole(QPalette::Base);
installEventFilter(this);
currentRegion.setTopLeft(startingPos);
currentRegion.setBottomRight(startingPos);
this->setWindowFlags(Qt::Dialog | Qt::FramelessWindowHint);
this->showMaximized();
}
void ClearBack::paintEvent(QPaintEvent * event)
{
Q_UNUSED(event);
QPainter painter(this);
painter.setRenderHint(QPainter::Antialiasing);
painter.setPen(Qt::black);
painter.drawRect(currentRegion);
}
void ClearBack::mouseMoveEvent(QMouseEvent *event)
{
QPoint currentPos(event->globalX(), event->globalY());
currentRegion.setBottomRight(currentPos);
this->repaint();
}
在具有纯色背景的小部件上,效果非常好,生成单个矩形。
但是,当背景设置为setAttribute(Qt::WA_TranslucentBackground);
发生以下情况。
先前绘制的矩形不会被“擦除”
有没有办法删除半透明背景上先前绘制的矩形,如果可以,如何删除?
另外,对于“奖励积分”,为什么这种效果会发生在半透明背景而不是实心背景上?
小部件与WA_TranslucentBackground
属性不会自动清除其背景。你必须:
更改默认的合成模式SourceOver
to Source
,
用透明画笔明确清除旧矩形,
绘制新的矩形。
下面是一个在 Qt 5 下测试的工作示例。您必须按下鼠标来绘制初始矩形并将其拖动;当您释放鼠标时,程序退出。
#include <QApplication>
#include <QWidget>
#include <QPainter>
#include <QMouseEvent>
class ClearBack : public QWidget
{
Q_OBJECT
QRect m_currentRegion, m_lastRegion;
public:
explicit ClearBack(const QPoint &startingPos) :
m_currentRegion(startingPos, startingPos)
{
setWindowFlags(Qt::Dialog | Qt::FramelessWindowHint);
setAttribute(Qt::WA_TranslucentBackground);
showMaximized();
}
Q_SIGNAL void regionSelected(const QRect &);
protected:
void paintEvent(QPaintEvent *) {
QPainter painter(this);
painter.setCompositionMode(QPainter::CompositionMode_Source);
painter.setRenderHint(QPainter::Antialiasing);
painter.setPen(QPen(Qt::transparent, 3));
painter.drawRect(m_lastRegion);
m_lastRegion = m_currentRegion;
painter.setPen(Qt::black);
painter.drawRect(m_currentRegion);
}
void mouseMoveEvent(QMouseEvent *event) {
m_currentRegion.setBottomRight(event->globalPos());
update();
}
void mouseReleaseEvent(QMouseEvent *) {
emit regionSelected(m_currentRegion);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
ClearBack back(QPoint(200,200));
a.connect(&back, SIGNAL(regionSelected(QRect)), SLOT(quit()));
return a.exec();
}
#include "main.moc"
本文内容由网友自发贡献,版权归原作者所有,本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容,请联系:hwhale#tublm.com(使用前将#替换为@)