feat: allows dragging to move around the canvas

[juliusl]

This enables holding down the middle mouse button to drag the canvas in order to move the scroll wheels.

Also, adds additional space to min-size so that the edges of the image can be more centered. (Not a Qt expert, but setting a layout didn't seem to fix the issue and this was the least intrusive option)

[wkentaro]

hmm, but the offset makes any newly open image offset by default:

even if we decide to run "Fit Window" after the offset in the beginning, just 500 offset means we can't move the image that freely.

[juliusl]

@wkentaro - I was wondering if you had any ideas on how to better implement that? I noticed if there isn't some extra space around the edges, it's not possible to center a portion of the image on the edges to the center of the canvas.

[spoonytripod]

The dragging feature is what I really wanted. Thanks! It works greatly. I hope this feature will be merged into the original branch.

I have one question. Would it be possible to change the image zoom in/out default setting from the current Ctrl + Wheel Scroll Up/Down to just Wheel Scroll Up/Down? This change would allow me to almost completely eliminate keyboard usage in my current workflow, which would be great!

[juliusl]

@wkentaro so I think I fixed the issue, could you give it a try and let me know what you think?

[juliusl]

I have one question. Would it be possible to change the image zoom in/out default setting from the current Ctrl + Wheel Scroll Up/Down to just Wheel Scroll Up/Down? This change would allow me to almost completely eliminate keyboard usage in my current workflow, which would be great!

@spoonytripod Hmm, that would probably need to be in a different PR, I suggest opening an issue/feature request. Since that isn't bound to a shortcut it's not something you can change from .labelmerc, which would mean it requires some code change around the wheelEvent.