Owner-draw QGraphicsItem Problem

[Dashi]

Hi,

I have to draw a custom graphics item on QGraphicsView, but the problem is APIs of QPainter are not sufficient for me to draw the item. So I create a QPixmap which is as large as the viewport, and draw my item on the QPixmap, then draw the QPixmap by calling QPainter::drawPixmap(). But this way is inefficient and need much more memory.

Is there any way to improve? Can I get the pixel buffer of the QGraphicsView and draw on it directly when QGraphicsItem::paint() is called?

BTW: I use raster graphics engine.

Thank you!

[giesbert]

Dashi,

what is missing in the QPainter API? And how do you paint on the QPixmap then? Afaik, you can't access the pixel buffer directly.

[Dashi]

Hi Gerolf,

I have some 2d NURBS curves, what I need to do is draw those curves, and fill the area enclosed. I have a function to calculate the color of each pixel in the area to be filled, so I cannot use QBrush directly.

Thanks!

[andre]

You need to use QImage to draw on pixel level.

[giesbert]

and the pixmap / image could be of the size of the graphics item, needn't be of graphics view

[Dashi]

Hi Andre and Gerolf, thank you both!

But the problem is: If the view is zoomed in, the item itself may be much bigger than the view...

[andre]

And that is a problem because...?