I'm new here, and here to cause some trouble. I just wrote my first GTK+3 app - or rather, I adapted an existing C++ program to give it a GUI with GTK+3, and the distinction is important for reasons I'll make clear. It wasn't a fun experience, and I'll try to keep ranting to a minimum, but I'm here to ask people to seriously and thoughtfully consider that gtk+4 embrace some new ideas.
1. Threads are here to stay
A number of years ago I was doing something in python and tkinter, and got a crash out of tkinter. I dug a bit and realized I'd found a tkinter issue, and there wasn't a workaround. Since I was stuck - and annoyed - I wrote my own GUI toolkit, specific to Windows (but using openGL) and python. Frankly it looked like crap, but it had the feature of features I'd always dreamed of - thread safety. Complete thread safety, invisible to the coder. You could delete a widget from any thread at any time, including from the click callback of the widget itself, and it sorted everything out for you. No explicit locking, no hangs or crashes.
I can't tell you how freeing this was or how much I've missed it since. Widgets are just resources and should be like any other resource. Think of files on linux. If one thread is writing to a file and another decides to delete the file, well, maybe you got what you wanted or maybe you didn't, but the operating system does not refuse your request, hang or crash. The file is your resource, and as such, you do what you want with it, from any thread at any time. The resource manager, in this case the OS, deals with it all, leaving you free to Just Code(tm).
My C++ application is now riddled with gdk_threads_add_idle calls. It has to be. It has a lot of threads, each doing independent tasks with sockets and things, and sometimes they want to update a label with new text or new colors. And instead of calling GTK and saying "do this", I now have a bunch of functions that have to get injected into GTK, each returning false. Now the code is ugly. And I'm not going to redesign it around some central GTK world view; the fact that it paints a screen with status is not the main point of the application and GTK shouldn't demand a starring role.
Abolish the concept of a main gtk thread. "Anything anywhere and real soon now" should be the motto.
"It has a lot of threads, each doing independent tasks with sockets and things, and sometimes they want to update a label with new text or new colors" .... this is just a sign of not using proper MVC design. stuff driven by the socket should change the model; the view should always update in response to changes in the model. if you design things correctly, this just happens.
2. My pixels, not yours. Hands off.
I know that Gtk has huge investment in flowing, springy, widget layout. Yay adaptability to new screen sizes. But sometimes, you know, I just want a widget to stay where I put it.Sure, if you're writing an app that has to adapt to a 2x3" phone's screen or a 20x8' foot, twenty billion pixel wall screen, having the GUI engine manage sizing is nice. And monitors keep getting bigger, so...
Except wait. They don't anymore. These days, there's small screens, desktop screens, and massive wall displays, and applications rarely cross from one to the other. When they do, they're already coded to adapt, because layout is philosophically different for a phone and a huge screen, and different in ways that the GUI engine isn't likely to be smart about without help.
In other words there's a place in the world for the ability to Visual-Basic-Style-I-said-
This-Big-And-Right-Here-and- no-backtalk-out-of-you nailing down of widgets, for specific niche applications. Maybe Glade can do this, but every time I Googled, I found threads saying "that's not the Gtk way".
One True Wayism can have merits, but not in GUIs. Make a GTK API that makes it easy to draw exactly what I want. My application is a fixed display on a wall, and I'm not happy to see fields shifting around because the very large Current Time field ticked over to skinnier numbers. (I'm sure this is fixable using the current toolkit - but apparently not trivially.)
3. I have to do what? Just to control colors and text in labels?
Maybe I did this wrong, but my goal was a black background, and then a bunch of labels of various sizes. I need to be able to update the text color and background color of the labels on the fly; everything from slow adjustment of text color to indicate changing states, to ohMyGoshAProblem! flashing labels at 4/sec because something's badly wrong. Simple, no?
Simple not. It took a few days and I still didn't get exactly what I wanted.
First of all, I learned the hard way that if you specify a widget's background color in Glade, nothing you do at runtime can change it. (That's probably overstated, but none of the existing or depreciated calls I tried did anything.) That's just a weird bug or documentation failure, but the upshot is that it's critical to specify as little as possible in Glade and do as much as possible in code. That's simply weird. And since Glade isn't making it easy to get the layout I wanted anyway, why did I bother with it?
Second, in other to get a black background everywhere, I had to use css. Not a lot of it: *{background-color: black;} got it done. But then there was learning curve with providers and those are tricker than they should be; it was a great moment when the window finally turned black. It should have taken ten seconds boring seconds in Glade. Why did I need a css file? What is this stuff about providers and screens?
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