Linux draws on screen regardless of Windows manager

Question

It is more a matter of vocabulary than anything else.

Introduction

I use the Point Cloud library to get face tracking data. Using this data, I want to track where the user is looking at the screen. It's not a problem.

Problem

To give the user feedback, I would like to draw an assessment of the face of the face in the form of a red circle on the screen, basically as shown here (they just create a tiny window). I would like this circle to be able to walk across the screen, and I want it to be always visible. I do not want it to be closed by another active window. If this impedes interaction with the window, I am fine with that.

My problem is that I don’t know where to start.

I could just control the cursor, but this is not so ideal, because I would like to still move the cursor while I use face detection.

I think I need to use OpenGL, but all the examples I saw were inside X windows. For example, the code that I found here after getting the hint here , give me a nice permanent window, but the window still captures all my mouse clicks. How to do something on screen with OpenGL independent of X-Window?

Am I completely approaching this from the wrong direction? If so, what should I look for in googling?

I will accept any answer that gives me a starting point.

Platform

I am using Ubuntu 12.04 with a Unity desktop.

Answer 1

Create a regular window. Tell WM to skip the ant scenery so that the window is always on top. Use XFixesSetWindowShapeRegion () to separately set the circular output area and empty input area. To do this, you need the XFixes build window manager.

You can also make the window translucent (this requires a layout window manager).

Modern tools like gtk should have easy-to-use APIs to do all of the above.

No OpenGL is required at any stage.