Since PureBasic 5.40 LTS, GTK3 is the default GUI toolkit used by PureBasic on Linux. It seems like a no brainer update for our users, but the fact is than GTK3 doesn’t fit well the PureBasic GUI library and we have several bad hacks here and here to make it work at all. We decided from the start in PureBasic to handle pixel perfect sizing of the GUI elements to allow maximum flexibity. For example, we added a Dialog library on top of it, which adds automatic layout depending of the font size, and allow to design complex resizable windows. It’s nice, but not mandatory, and depending of your needs, you will or will not use it. Up to GTK2, it was the same: you could define pixel perfect size and the toolkit would honor it. Now, it’s a different story: the toolkit can decide if the size you gave programmatically is too small or not. It’s a big change, as you could end up with a deformed GUI and more important, the running program doesn’t reflect the code entered by the programmer. You may wonder why such change has been implemented ? My guess is to force use of layout for everything, so the toolkit can support themes more efficiently and without change from the programmer. It may be true, but it’s one of the first toolkit to do so and forcing the programmer hand isn’t always a great thing, especially when it removes flexibility: you can write a layout engine using pixel perfect sizing, but you can’t do pixel perfect sizing with a layout engine. And for some specific apps, running on proprietary OS, it can be an issue as theming is irrelevant.