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:

QPointF pt=mapToScene(event->pos());
         this->scene()->addLine(pt.x(),pt.y(),pt.x(),pt.y(),QPen(color, size));


Here's a screenshot:

enter image description here

On the left, it descends more slowly, faster.


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1 answer

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;



I was moving very fast and getting spaces (now my mouse button is pressed)

enter image description here

now i have released my button and i get a normal curve

enter image description here



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