Looks good. Also it looks like there are a ton of memory leaks in this code. Perhaps can tackle that in a follow up change. Some of these new char can also be changed to stack buffers.

Yeah, I noticed that as well. I'll try to make some time to open a new pr for the memory leaks.

Would you say that this would be the right approach? (Char vs. char and sizeof vs. 60)

Char percentages[60];
GetDlgItemText(... percentages,sizeof(percentages));

EDIT: On second thought, it's probably preferable to put those memory leak fixes in this pr instead of a separate one.

Would you say that this would be the right approach? (Char vs. char and sizeof vs. 60)

Yes this looks good.

On second thought, it's probably preferable to put those memory leak fixes in this pr instead of a separate one.

You can do that yes.

I think the memory leaks are handled now.

Did you test this change? Does it work?

I haven't been able to test, so I'm afraid I can't answer that.

It would would be good to give this a brief test before commit.

I have increased the percentages buffer sizes to 200 to hold a string like "1,1,1,1 ...." (100 * '1' + 100 * ','). From my brief testing the issues that this pr addresses appear to be fixed.

I did notice, however, that creating a new horizontal slider immediately crashes because of a nullptr dereference in getImageWidth().