i need to create a GUI app that will run on a windows PC, Linux X11,
Windows CE PDA, and the Nokia N800.

It will be basically a dockable tool bar with some floating bitmaps. It's like the bottom bar in windows with the start button. Normally it's docked, meaning all the other windows are smaller than full screen and make room for the dock. But you can also make it auto-hide, in which case all the windows are full-screen and go to the bottom of the screen, but when you move your mouse over the bottom edge, then it pops up on top of the existing windows. This app I need will work the same way, it will have 3 modes: 1) free-floating popup, like a normal window. 2) docked toolbar that stays locked at the top, left or right of the screen and the desktop and all other windows are reduced to fit within the dock, and 3) auto hide where it's on the top, left, or right of the screen but hidden until you move your mouse over the edge and then it
appears.
Can u tell me if GTK can help me with this? Maybe u can tell me other GUI development toolkits to achieve what I want.

Didn't Nokia recently buy Trolltech? Some phone company did. Trolltech makes Qt, another GUI maker like GTK. So, you might want to look at Qt, especially since it has a mobile phone library plus it's cross-platform.

That being said, GTK should work fine also. I just don't know how well it works on cell phones.

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