I have been working on a simple GUI and have hit a roadblock. I haven't found any examples or even readable source on how to create a GUI layout manager. I was wondering if anyone knew of some resources on creating one, or some source code that isn't cryptic like Qt's layout engine.
Thanks.
It depends on what you mean by "layout manager", and I'm not familiar with Qt, so that doesn't give me much of a clue.
If you mean things like resizable window handling, though, I think the relevant term is "constraint solver". I've never looked into it that much, but I believe GUI constraint solvers are based on linear programming - the Simplex algorithm and all that. It might be possible to do something with Gaussian Elimination, but I'm far from confident about that.
Based on a quick search for "gui layout linear programming", you might find this paper from CiteSeerX interesting - there's a PDF download. If you don't like cryptic, well, at a glance at least it's not exactly math heavy, but I suspect it's not light reading either. I guess I'll find out shortly, as you've got me interested.
I am currently making a Windows port for Mozilla XUL. My approach does not involve linear programming techniques like Steve mentioned, but it is a more object oriented approach. It is based on the Composite and Decorator design patterns.
The composite pattern allows you to create controls that have child controls, which in turn can have their own children. A control is responsible for positioning its child controls within its designated client rectangle.
For example suppose you want to implement a layout that positions its child controls horizontally. The layout algorithm then needs to calculate the width of each child control in order calculate the x offsets for each child control.
Calculating the width of a container is done by returning the sum of the widths of the child controls.
The Decorator classes can be used to add extra properties. For example a MarginDecorator can add spacing between child controls, a ScrollDecorator can scrollbars, etc...
It's a fun thing to do, I wish you good luck!