Raspberry Pi support

[techyian]

Removed GLES directory and brought forward relevant changes required to run GLES into renderer 1 directory. CMake changes for correct linking to GLES and Broadcom lib. Added install notes for RPI. Tested on Raspbian using full OpenGL and GLES.

[rmarquis]

Someone was able to run OpenGL on RPi simply with:

ztealmax: actually just used:  git clone https://github.com/etlegacy/etlegacy.git and added this to easyconfig.sh under -RPI section:
            BUNDLED_SDL=0
            BUNDLED_OPENAL=0
            FEATURE_OMNIBOT=1
            INSTALL_OMNIBOT=1
but im using OpenGL not GLES.

[techyian]

Hi Remy,

I haven't looked over the Raspberry Pi support for a while now due to issues on the Raspberry Pi 4. Currently on the Pi 4, you're not able to run the game directly off the framebuffer using SDL. I believe support will eventually become available, but not any time soon unfortunately.

After discussing with the etlegacy devs, it was agreed that the GLES folder should remain and not all be merged into the GL folder with ifdef everywhere. My latest work on this can be found at this fork and also here for etlegacy-libs.

When I last looked, Raspberry Pi 3 worked great, Pi 4 worked well with full OpenGL and had great performance improvements over Pi 3, but I think I recall GLES having issues. When moving the mouse to the left, the mouse cursor would appear briefly and stop the camera movement. I'm not sure if that's an issue with the game but makes it quite unplayable with Pi 4 & GLES.

Skyhawk was keen for Pi 3 & 4 using both GL and GLES to be working well before any official builds could be put out. Would it help if I do some testing again to see what the current status is?

[rmarquis]

I see. We don't have anybody testing RPi builds in the team, but feel free to let us know if/when something can be merged. I don't think much has changed since last time you looked into these issues.

I'm not sure having both GL and GLES fully working is required before a merge, but having at least one of these working correctly would be a must.