resizeable rubber band with QSizeGrip

pmh4514

Hi - I'm using Qt 5.14 on Win10 x64

Trying to implement a resizeable "rubber band" for ROI selection over an image, using what I found here as the accepted answer on StackOverflow:

https://stackoverflow.com/questions/19066804/implementing-resize-handles-on-qrubberband-is-qsizegrip-relevant/19067132

My code is exactly as in the example.

Generally it works as I expect. However, in the above example, the size grip in the upper left is pointing up and to the left (and can presumably adjust the ROI up and to the left) and the one in the lower right is pointing down and to the right and can adjust the ROI down/right.

My lower right QSizeGrip works and looks as expected and I can use it to expand my ROI down/right as I'd expect. But the one in the upper left is not painted pointing up/left like it is in the stackoverflow example, it looks the same as the one in the lower right. Dragging it left/right adjusts my ROI as expected, but dragging it up/down is exactly the same behavior as dragging the lower right sizegrip, where the upper left corner of the ROI is anchored, rather than actually resizing it in that direction.

I realize the stack overflow example is quite old and against an older version of Qt, but does anybody know how I can make it so the two drag handles can expand the ROI in both directions as expected?
Thanks!

SGaist

Hi,

Can you provide a minimal compilable example that shows the behaviour you have ? There might be something unrelated to the stack overflow code happening.

pmh4514

Good idea. Of course, putting together a simple empty QMainWindow project with a single QLabel taking on the rubber band functionality, it works as I'd expect it to. Meaning the behavior is due to something elsewhere in my real project.

SGaist

That's a good news.

Then I would disable all widgets that are not related to your rubber band and gradually add them back until things get wrong.

pmh4514

Yah I started looking at how I was setting it up and controlling it - the GUI interaction of this particular app positions the rubber band automatically at previously user-defined positions. I was calling setGeometry on it with a QRect whose coordinates were reversed. (interestingly to no visual detriment.) Now that I've changed that, the QSizeGrip handles do function as expected, I can resize up/left just as well as down/right.. The upper left arrow itself is not pointing the correct direction (up/left) but at least now it's behaving as expected.

SGaist

Then there must be one last glitch hiding.

pmh4514

I'll have to dig into the QSizeGrip code to see what determines its orientation

SGaist

There's a method in the private implementation of the class that determines that based on the position of the grip.

pmh4514

yah I'm seeing that.. Interestingly it's being painted in the correct spot (and now behaving as such) but it's being painted as if it's the lower-right

Pl45m4

@SGaist said in resizeable rubber band with QSizeGrip:

Can you provide a minimal compilable example that shows the behaviour you have ?

This in Top 3 of "solutions which will fix your Qt problem" 😂😂
RubberDuck Debugging ;-)

pmh4514

Indeed it is!

I'm going to mark this solved. I haven't figured out yet why my TL corner is painting as if LR, but that's beside the point I think.