FreeBSD support

[iceiix]

Supporting FreeBSD could be useful to help diagnose platform-specific issues and improve compatibility, and shouldn't be too difficult since Linux is already supported

[iceiix]

Able to build Steven after installing SDL2 as follows:

pkg install sdl2 sdl2_gfx sdl2_image sdl2_mixer sdl2_net sdl2_ttf
export LIBRARY_PATH=/usr/local/lib

[iceiix]

Above commands are sufficient to compile, but the FreeBSD system I'm testing on is headless, so additionally installed (may not all be necessary):

sudo pkg install tightvnc
sudo pkg install mesa-libs
sudo pkg install mesa-dri
sudo pkg install driconf
sudo pkg install xorg-vfbserver
sudo pkg install x11vnc

then can run Xvfb (from xorg-vfbserver) to create an X virtual frame buffer:

Xvfb :2 -screen 0 1024x768x24 +extension GLX +render

convenient to use x11vnc: http://www.karlrunge.com/x11vnc/

x11vnc: a VNC server for real X displays

x11vnc allows one to view remotely and interact with real X displays (i.e. a display corresponding to a physical monitor, keyboard, and mouse) with any VNC viewer. In this way it plays the role for Unix/X11 that WinVNC plays for Windows.

configure a password in ~/.vnc/passwd per the instructions (or don't), then expose the X desktop (I used :2) over port 5900:

x11vnc -display :2 -rfbauth ~/.vnc/passwd

run DISPLAY=:2 target/release/steven, and although it is slow using software GLX, it works:

happily, the "entities are not visible" bug doesn't appear here (https://github.com/iceiix/steven/issues/25), at least, as indicated by the visible sun