Access to a monitor not containing the desktop

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http://stackoverflow.com – On a computer with multiple monitors where the desktop is not shown on one of them, is there any way to draw on that monitor from a program? Reasoning: I need to display a variable image full-screen on a separate monitor, without the user being able to disturb the screen with the mouse or without being able to shift windows on top of my image. Example: a computer has one monitor and one projector connected; the monitor shows a "normal" desktop and the projector shows the generated image (say, a color gradient). The first use would be on Win7, but if a portable solution exists, an X11 solutio (HowTos)