CODEWITHSUNDEEP
linuxopengl
tambalolo
tambalolo

Reputation: 1075

Backgroundless and Windowless OpenGL application

Have you used or seen cairo dock in linux? I've read in wikipedia that's it was written in C. I'm just curious how did they make a windowless, widget-like app which use OpenGl. Is it possible to make an OpenGl application which is windowless and has no background(or transparent background). Did they made it with C from scratch? or Did they used any other tool?

Upvotes: 0

Views: 453

Answers (1)

datenwolf
datenwolf

Reputation: 162367

What do you mean by "windowless". A window is the (rectangular) region on screen to which you can draw with drawing operations. From your question however I have the impression, that you're actually asking about creating a window without decorations (i.e. title bar, etc.).

In Linux, or more precisely X11, the appearance of a window is controlled by two things: The Extended Window Manager Hints (EMWH) for a window under control of the window manager; the window manager is the actual program responsible for drawing the decorations and borders. And the Redirection Override flag, which controls, if a window actually gets to be under the control of a window manager. If you're asking about "backgroundless", then I presume you mean, transparent. First have a look at this video I made: http://www.youtube.com/watch?v=iHZfH1Qhonk Is this what you're after? Then what you actually want is a window with an Alpha channel in its framebuffer config (X11 XRender FBConfig), together with a compositing manager (which can, but isn't required to be a part of the window manager). The sourcecode for this program can be found at https://github.com/datenwolf/codesamples/tree/master/samples/OpenGL/x11argb_opengl_glsl

Or are you actually asking about a OpenGL context to which you can render a picture, but without it appearing on screen? That would then be an off-screen context and there are two ways for implementing this with X11:

  • Using a windowless PBuffer X11 drawable for the context

  • Using a hidden window together with a OpenGL Framebuffer Object

Both methods have each their pros and cons.

Upvotes: 1

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