Canvas problems

[Tommytrojan]

Thanks for the quick answers.

The problem is not the zooming, it just exacerbates the problem, so I put it in the little sample program.

The problem is not the bounding rectangle either, I stripped it down to the code listed in my initial post which uses a QCanvasRectangle with no subclassing whatsoever. The effects I see are not typical for an improperly set bounding rect either. It seems to be related to some kind of rounding or update error in the canvas view. It might be fixed in the current 3.3.6 version. If you can run the sample program and your application does not show these distortions most likely this has been fixed. I'm wondering if I should upgrade (which I probably won't if the bug still persists in 3.3.6).

Cheers,
Tommy

[wysota]

But are those red lines the distorsions of the square? The square has black outline and the distorsions are red...

[Tommytrojan]

Probably, I played around with different versions so I get the biggest impact, one of them was with a red pen so the outline of the rect was red as well. I must have used that screenshot. In general it doesn't matter what shape or color you use this happens with all canvas items I have seen so far. There is a sample canvas app which has the same effect. Now maybe if it doesn't happen on your system and you run a newer version of Qt than 3.3.1 it might have been fixed in the mean time (I hope so).

Tommy

[wysota]

I translated your app to C++ (see attachment). It doesn't show the artifacts you describe. If you resize the window, it shows some garbage, but not connected with the rectangle (see other attachment).

[Tommytrojan]

Your C++ implementation looks like what I would have done. If you take another top level window and draw it "slowly" over the rectangle you don't see any distortions? Which version of Qt are you running? Maybe it is time for an upgrade. Thanks for your testing, that is really very helpful.

Cheers,
Thomas

[wysota]

If you take another top level window and draw it "slowly" over the rectangle you don't see any distortions?

I do, but not connected with the rectangle (see attachment).

Which version of Qt are you running?

3.3.5

[jacek]

Either I'm too fast or everything is OK on my system (PLD Linux, Qt 3.3.6, PyQt 3.15.1).