Dear @leo603222 , welcome!

I am sorry, I haven't had time to look at this in detail yet. But your proposed changes look very reasonable, and seem to give a good explanation of what has been going wrong in the first place!

What I am wondering right now is how does the presence of the grid make this work/fail?
My wild guess is that the AxisItem intercepts the initial event and fills in some of the position data based on a different coordinate transformation than the ViewBox would normally do.

I guess you might have a better understanding of this after your experimentation... Would you mind sharing that with us?

@NilsNemitz , there's a big difference between grid on and off.
When gird is on, the mouse drag event is triggered by the AxisItem, when grid is off, the mouse drag event is triggered by ViewBox.
So with grid off, ev.buttonDownPos() return a position in the coordinate of ViewBox, which is right for r = self.childGroup.mapRectFromParent(r) in updateScaleBox().
But with grid on, ev.buttonDownPos() return a position in the coordinate of AxisItem, which is not consistent with the need of self.childGroup.mapRectFromParent(r) in updateScaleBox().
By using scene coordinate in these two places, I think this problem is fixed.

Hi @leo603222 Thanks for the PR!

Around these parts we get nervous when it comes to changes to ViewBox.py, not because we think it's bug-free, we know it's not, but because making changes there can have very subtle other issues.

That said, as @NilsNemitz said, the changes look very reasonable, I'll try and test it out against the test code in the issue you referenced in the next day or so, since the test suite passes, and if I can verify the PR fixes the issue as described I'll merge right away.

Also FYI, when you make a PR, it's easier for us if you don't name your branch the name of a branch in this repository. The reasoning being that I can't just git switch master to hop on your branch to test things for myself (we can work around this by having a different local branch name that tracks to your fork).

Your first PR modifying ViewBox.py is an impressive feat 😆

I've verified the PR works as intended; I'm good to merge. I would prefer to leave the change to LegendItem.py to be part of a separate PR for tracking purposes. 👍🏻

Hi @leo603222 I wrote this late last night, didn't mean to imply you should close out this PR; I was able to clone into your branch; I did have to run a more complex command due to the branch naming, but it wasn't some insurmountable task :)

In case you're curious, if someone has a branch name something like fix-issue1000 and if I want to hop on that branch to experiment I would run the following commands

git remote add pr-author-username https://github.com/pr-author-username/pyqtgraph.git
git fetch pr-author-username
git switch fix-issue1000

In the case where there is branch naming conflicts, as this PR had, for the last command instead of the git switch I run

git checkout -b pr-author-username-master pr-author-username/master

but I have to stack overflow it each time because I always forget 😆

Anyway Hope you submit the changes to ViewBox.py, I tested them out and can confirm they worked, and would love to merge the changes 👍🏻