QGraphicsItem paint delay

Question

What could be the possible reason for this? When i zoom in the QGraphicsView and move the QGraphicsItem, I get this weird result. It does update if I zoom or pan the View again or if I focus on other widgets. Im using PySide. And the painter function is this

def paint(self, painter, option, widget):
    if self.isSelected():
        brush = self.highlight_brush
        pen = self.highlight_pen
    else:
        brush = self.dormant_brush
        pen = self.dormant_pen

    painter.setBrush(brush)
    painter.setPen(pen)

    painter.drawRect(0, 0, 100, 100)

Why does this happen even for this basic paint event? This problem is not seen if there is no Pen. If I increase the pen width, this issue is disturbingly visible.

Answer 1

I don't know the actual solution for this rendering artifacts. But, updating the view during mouseMoveEvent did fix the issue.

 def mouseMoveEvent(self, event):
    QGraphicsView.mouseMoveEvent(self, event)
    if self.scene().selectedItems():
        self.update()

Answer 2

The error you are seeing is probably because parts of what you are drawing are outside the bounding rectangle. My guess is you are using the same values to calculate the rectangle you are drawing as you are to calculate the bounding rectangle. Applying a pen then will make the drawn rectangle wider than the bounds and so will result in the smearing you are seeing.

Answer 3

I had the same problem. This is my solution:

As @Nathan Mooth said, the problem was that I was drawing outside of the boundingRect, so I just made my rounded rectangle(what I'm drawing in the paint() method) 10 units width and height less than the boundingRect:

 # Setup Rect
        frameRect = self.boundingRect()
        frameRect.setWidth(self.boundingRect().width() - 10)
        frameRect.setHeight(self.boundingRect().height() - 10)

This is how it was looking before(GIF):

This is how it looks now(GIF)

Note: I added color selection and changed the color of the drop shadow. So it looks a bit different.