Drawing line in QGraphicsScene with Qt
I have a problem with drawing lines. It works well when the mouse moves slowly, but when the mouse moves faster there are some gaps and I don't know why. This is the code:
if(QEvent::MouseButtonPress&&event->buttons()==Qt::LeftButton){
QPointF pt=mapToScene(event->pos());
band->setGeometry(0,0,0,0);
band->hide();
band->update();
this->scene()->addLine(pt.x(),pt.y(),pt.x(),pt.y(),QPen(color, size));
qDebug()<<event->pos();
}
Here's a screenshot:
On the left, it descends more slowly, faster.
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So this is a really interesting question. I am doing the same on my computer and getting the same problem. I am not reading your code deeply because it seems like you are subclassing QGraphicsView
, but I am subclassing QGraphicsScene
, but it doesn't matter. I am telling you the basic idea. I can offer you the following:
Draw it as it is, but when drawing the custom end, you will remove that and draw 1 very nice curve without those gaps. You must use mouseReleaseEvent
:
In mouseMoveEvent
:
QPoint pos = mouseEvent->scenePos().toPoint();//just get point
pol.append(pos);//append to polygon
//...draw lines or what you want
In the constructor:
QPolygon pol;
In mouseReleaseEvent
you create QPainterPath
, load a polygon onto it and draw a normal line with no spaces.
void GraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
QPainterPath myPath;
myPath.addPolygon(pol);
addPath(myPath,QPen(Qt::red,2));
pol.clear();
}
Result:
I was moving very fast and getting spaces (now my mouse button is pressed)
now i have released my button and i get a normal curve
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