OpenEuphoria

*Cough* Redy *Cough* LOL

But seriously, that's exactly what I did with Redy, except it's pure euphoria. I wrapped all the basic win32 api to create windows, handle events, and draw to bitmaps. Eventually, I added more advanced features like clipboard functions. It took me years, and it's still not finished. But, I learned so much from it. I gained a good understanding of the foundational win32 api. Those concepts can be carried over to linux. I haven't had time to port Redy to linux yet, but I basically understand how it could be done. I also learned a ton about optimization! The first few versions of Redy were horribly slow, but the version that RedyCode is built upon is amazingly fast, except for a few odd things here and there. I also learned a ton about important programming concepts, such as object-oriented and reactive programming. Even though Euphoria doesn't technically have those features, I was able to structure my code in a way that followed those concepts. And I also learned a lot of things that I could have done better, and would like to improve, but it would require a lot of rework.

I would suggest looking up the API documentation for windows and/or linux for creating windows, handling events, and drawing graphics. All the general API stuff. Ignore the controls/widget libraries, just look at the raw graphics stuff, and learn how to handle mouse/keyboard events, and draw/load/save bitmaps in memory, and how to manipulate windows and draw to them. It will take a lot of planning and good structure to define your own widget classes and how they interact with each other, as objects in a tree, with parent/child relationships. It's a lot of work, but it's definitely doable and is a great learning experience!