How to make a window manager?

Question

I tried writing code several different times, but I came to an error with each one. Basically, I'm trying to make "windows" similar to say Explorer, Paint, MediaPlayer, where you could drag then around, interact with them, minimize and close. Of course, if you clicked on a window, the one below it (they can overlap) shouldn't get affected.

I know how to do this, I have a list of the class I call Window, loop through it, and I only interact with the first window to contain the location of the mouse-click. This way, other windows overlap won't get affected.[1]

Next, I had to make it so that two buttons that are overlapping don't get activated when the user clicks in the "intersection of both buttons." I handled this by using the same method I used above.[2]

But the problem I'm facing now is that, if I hold the left click, but then I decide not to click a button, I drag the mouse away from the button, and release the left click, so that the button-click event won't be activated. But, when I remove the mouse from the boundaries of the button, and say, into another.. the new button get activated. Which it should not.[3]

My set up is like this: I have a class called Window. In Window, I have a list of the class called Interface (similar to the Control class in WinForms). And each Interface has a struct in it that contains 4 bools, if the left/right is currently down, and if they were down in the previous processing. (prevLeft, prevRight, currLeft, currRight)

So, I'm ready to discard that (I have not yet, so I still have the source code), but I need a good structure for making an object-oriented type of application. However, I am not using WinForms. I need help with the structure alone, so no actual code is necessary, description is enough. I need to avoid the 3 problems I mentioned above.

user1306322 · Accepted Answer

Creating your own Window Manager is not an easy task. I know it because I'm making one too ;)

You can use an existing, though maybe not the best solution, like for example Nuclex.UI, which I personally rejected when I first saw it, but if you're not dead set on making your own WM, I suggest to use that or hybrid WinForms-XNA approach.

But if you're really dead set on implementing a custom Window Manager, you have to understand how any other WM works. Since we're talking about XNA, it means Windows, and that means Windows Explorer, which is a great thing to learn from.

You have to recognize how the simplest things work, and it's really not so hard. The hard part is figuring out what logic is updated when, and how to not spend all the CPU on only UI updates. Let me just give you a few hints on how to solve the problems you mention in your question.

To keep track of all windows, I'm using a Dictionary, where Window is a custom class, and the string is its unique name for rare cases where I have to call windows by name. Think of it as a window GUID or Handle. But you can just make it so that a "Form" can only appear once, and store all references in static variables.
To make WM understand what control you're clicking I use rectangles and check if they contain a Point which is at Cursor coordinates and has {1; 1} pixel size, which is probably about the same way it's done in Windows Explorer. To do that your WM needs to know in which order to update the active windows. Usually you'd want to start from the topmost window and continue towards the end of the list of active windows. For that you can just iterate through the list with a foreach loop.
But that's not all, because every window itself is a Container, which means it contains other controls, some of which may even be Containers themselves, like WinForms Panel class. This means you have to iterate through each of the Windows' Children controls. The update order should make sense too - update from the topmost child to the bottommost, recursively for Container controls, in case they also have Containers in them. This basically means you'd want to implement a recursive GetAllControls() method for your WindowManager class that would iterate through all Containers and return a list of all Controls.
Drawing all those Controls should be done in reverse order of updating them, so you can just GetAllControls().Reverse() and iterate through that in a foreach loop.
Where to draw and what to update depends on all the parent containers the current container has and their combined offset from the top-left corner of the game window. I solve this by storing a ParentContainer reference in all children controls to get the appropriate DrawRectangles and update areas via recursive properties.
When you click somewhere on the screen and a click is registered on a Control, make the WindowManager remember that (bool clickRegistered) and not run any OnClick events on any underlying Controls.
Windows Explorer remembers the control you clicked and will activate its OnRelease event if the cursor is then released in the update area of the very same control. So basically Windows Manager only does something when you release the mouse button. You can make your WindowManager and Controls to handle click events differently, like firing an event right after you press the mouse button, i.e. OnMouseDown. But remember that Microsoft aren't noobs and there's a reason for that behavior in Windows Explorer, and it's because if you accidentally press a mouse button somewhere you didn't intend, you can still fix it by moving the cursor outside the pressed control's update area and not run its action.

At this point you might be thinking "Is it really worth implementing all this?" For me the answer was "maybe", because I was a total noob in both C# and XNA at the time I started, and now I know my game, which was originally supposed to use some Window Manager, is going to benefit from my own WM implementation far more than from ready third-party solutions. And besides, it's a great exercise in logic and programming.

But if you'd like to think of yourself as a game developer, you should think in terms of reaching your goal as quickly as possible, i.e. actually making a game, and not the game engine. So in this case, better make use of existing solutions and start selling your product.

How to make a window manager?

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