I have my framework set up to use tranformations and al_set_clipping_rectangle() to create views which can be drawn into. My framework sets up a default view which translates and clips things such that the "virtual display" is centered and black bars appear around the edges to maintain the aspect ratio.

This has been working nicely for me for a long time, but I was doing some testing on Ubuntu 13 and noticed that when using full screen mode, there tended to be some graphical artifacts left in buffer.

For instance, when the program starts, some of the graphics on the desktop remain in the buffer and show up in my program's window. It seems that Ubuntu is doing some transitional animation which affects the buffers even while my program is using the buffers, thus I end up with some of the desktop graphics being rendered onto the buffer and displayed in my program.

As a workaround, I had the entire screen cleared each frame before I set up my view transformation and clipping during the intro screen. This worked well, but then I tried Alt+Tabbing away and back to my program. The artifacts were back.

I changed the framework so that it would automatically clear the entire buffer for a couple of frames when the program regains focus. This wasn't enough to eliminate the issue since I can't figure out exactly when Ubuntu is going to decide to put stuff in the buffer.

Thinking about it now, I am wondering if it is ever safe to assume the buffers aren't going to be modified from outside my program. I had always assumed that only things I do within my program can affect the buffers that my program is using. I have never had issues on other platforms.

Does anybody have any thoughts on how I should deal with this? I am wondering if I might be able to use ALLEGRO_EVENT_DISPLAY_EXPOSE to determine when I should be clearing the entire buffer. I hate to waste resources redrawing black pixels over and over unnecessarily.

What video card and driver? It really shouldn't do that.

It's a netbook with an Intel Atom N570 running whatever driver comes with Ubuntu 13.04.

IF anything is modifying your buffers, its a bug. A good driver and/or compositor only reads from your buffers, not writes to them.

It's probably the Gallium driver which is pretty buggy. But there's not much else for most Intel chips.

Oh, is that the GMA500 hardware again? Most intel GPUs are supported by the intel-gfx i915 driver. The GMA500 is about the only "intel" gpu that isn't supported by the i915 driver, as its based on a powervr gpu.

A driver bug? I guess it might be similar to the Unity bugs that were in the initial 13.04 release. There were artifacts in certain parts of the UI similar to what I'm experiencing.

If that's the case, I'll just have a config file setting to work around the issue for those that are experiencing it.

It's that or ubuntu's unity bull crap.

I don't know if it's GMA500, but all Intel goes through Gallium now AFAIK.

Yeah, maybe try a different WM, one that doesn't do compositing and see if that works around the issue.

As far as I know, that is not the case on debian.

Some research says the official drivers are plain old Mesa+DRI/DRM drivers, while there is an unofficial incomplete third party Gallium driver for the Sandy Bridge and Ivy Bridge HD series gpus.

And as of April it was marked as a toy driver. Any distro using it by default would have to be stupid.

Thanks for the info, guys. I have implemented a workaround to deal with this issue.