My application, which is normally very stable, tends to hang when not the active window whenever I run with set_display_switch_mode(SWITCH_BACKGROUND). I am calling acquire_screen() and release_screen() before and after any writes to the screen, but this doesn't seem to help.

I'm using Allegro 4.2.0 under Windows 2000 professional and Visual Studio 2005.

Can anyone get SWITCH_BACKGROUND to work?

You're not doing anything else except blitting operations to the screen between those calls are you?

I am only doing circle(), line(), rect() and draw_sprite() between the acquire and the release. I am using double buffering so I do most of the normal drawing to my active page, and then I call draw_sprite(screen, active_page, ..)

I take it you know switch_background doesn't actually work in windows fullscreen mode?

I'm running in windowed mode with videomode GFX_GDI. SWITCH_BACKGROUND works in this mode, right?

I can only imagine so, but you should always test the return value. In my code I allow swapping between windowed/fullscreen and various other modes so I simply code for the bare minimum that should work for windows and other o/s's, as in:

You did remember to checkthereturn value, right?
If that doesn't work (but BACK_AMNESIA does), you probably should not be writing to screen when your program is swapped out.

I wouldn't know, but why don't you check the return value and find out?

I changed my video mode from GFX_GDI to GFX_DIRECTX_WIN and the hangs have stopped.

By the way, the call to set_display_switch_mode(SWITCH_BACKGROUND) was returning 0.

Thanks for the help everyone!

Any particular reason you're not using GFX_AUTODETECT_WINDOWED? If not, you should use that instead of any other driver.