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I have a Raspberry Pi with a GPIO display. I currently have it set up as a framebuffer device at /dev/fb1. Is there a way to make it my default or primary display for X windows? I'm ultimately trying to draw graphics to it, I was originally planning on using DirectFB and SDL, but DirectFB is in alpha for the pi. I've tried using SDL1.2 as well since it has Framebuffer support, but I can't figure out how to get SDL to choose a framebuffer device to draw to without using DirectFB.

I considered using SDL to prepare each frame of my simple GUI as a raw image and use mmap to blit it to /dev/fb1 instead of using SDL's built in draw functions, but I feel like this is a poor way to achieve my goal.

I think that if I can get xorg to use my framebuffer device as the primary monitor, I wouldn't have to worry about doing anything special to have SDL draw my image files. But I'm not really sure how xorg really works and if this is possible.

Any insight or help anyone has would greatly help! I've been butting heads with this problem for a week looking at different possibilities.

Julian
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1 Answers1

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With SDL2 on Raspbian you can draw directly on a framebuffer without using X at all. The graphical window is always full screen. You can start the code from console mode (with X stopped or from LXDE with X running, the idea is that SDL2 won't use X).

Unfortunately, Raspbian doesn't come with SDL2 (the SDL2 from Jessie doesn't work) so you will need to build it yourself (takes about an hour). Here is a description of the process of building SDL2:

sudo apt-get install build-essential libfreeimage-dev libopenal-dev libpango1.0-dev libsndfile-dev libudev-dev libasound2-dev

Download the sources for SDL2 from https://www.libsdl.org/download-2.0.php . Assuming that your downloaded file is called SDL2*.tar.gz, you can build and install it with:

cd ~/Downloads
tar zxvf SDL2*.tar.gz
cd SDL2*

./configure --disable-video-x11
make
sudo make install

After that, you should be able to link any C++ program with SDL2, e.g:

g++ my_program.cpp -lSDL2 -o my_program
./my_program
JeanC
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  • Is there a way to choose which framebuffer device is used? When I tried using SDL2 last time, it always defaulted to fb0, but I need it to use fb1. – Julian Oct 06 '14 at 15:00
  • Not sure if this will help, but you could try to use SDL_GetNumRenderDrivers and see how many options you have. If you have more than 1 try to select the respective driver with SDL_CreateRenderer and see which one (if any) renders on the fb1. I didn't find any function in which to specify directly fb0 or fb1. – JeanC Oct 06 '14 at 21:33
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    Apparently SDL1.2 has an env variable SDL_FBDEV that you could use to select the framebuffer to use, SDL_FBDEV see http://sdl.beuc.net/sdl.wiki/SDL_envvars – JeanC Oct 06 '14 at 21:43