A bit of sample code that demonstrates a quick-and-dirty way to implement a rootless mode for an emulator that has one huge back buffer in which it draws all its windows.

"Rootless" means that the emulated windows can be shown interleaved on the screen with platform-native window, like many commercial emulators and the Mac's Classic environment used to do it.

The design goal was to provide an easy way to hook in source code that assumes it has control over the machine. Your emulator's main function runs (renamed to EmulatorMain()) in its own thread and uses a few callbacks to talk to the actual Mac application framework. That way, its menus stay available even when the emulator itself hangs.

The emulator needs to register every rectangle that should show up as a window with this library. As such, this approach is not suitable for emulators that do not know what OS they run on, and you might have to hook into the host OS in some way to be notified when windows appear, are moved or go away.

It is intended as a demonstration of how it would work. As such, it currently only handles mouse events, though keyboard events could be implemented the same way.

Right now, back buffer updates are rather heavyweight, as is every API call. While it works and should be sufficiently fast for emulating older machines, one could speed it up significantly by using OpenGL directly and just uploading the pixel buffer to the screen. Maybe even use shared GPU memory for the back buffer and support partial updates only of changed areas. Similarly, the inter-thread communication could be rewritten in lower-level code, as we're really only sending across four numbers.

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Copyright 2003-2014 by Uli Kusterer.

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