Redirect raylib output to Framebuffer 1

Based on answer by Morphology user on raylib forum:

There is no particular magic to what I am doing. The first stage is to get the TFT screen working with the Raspberry Pi. In my case I am using one based on the ili9340 TFT controller, with an ads7846 touchscreen controller. These use SPI Bus 0 and 1, so SPI has to be enabled.

Nortro's TFT drivers are now built into the latest Raspberry Pi core, so to get this screen working on the Pi, you just need to edit /etc/rc.local and add the following just above the existing script that prints the IP address:

modprobe fbtft_device custom name=fb_ili9340 buswidth=8 speed=16000000 bgr=1 gpios=reset:27,dc:22 rotate=270

NOTE: bgr=1 is necessary on my TFT as red & blue were reversed. rotate=270 because of the orientation of the screen. If not needed, leave them off.

Edit /boot/config.txt and do the following:

Take the comment off the line dtparam=spi=on

Add the following in the sections entitled #additional overlays and parameters are....

dtoverlay=ads7846,penirq=17,speed=16000000,xohms=100,swapxy=1

again, swapxy was because of my screen orientation.

This gets my TFT working, and I can test it by typing the following at the command line, which directs the console output to fb1:

con2fbmap 1 1

and back again with

con2fbmap 1 0

Then, to mirror fb0 to fb1 continuously I use raspi2fb available from github, along with build and install instructions.

Finally, I added the following lines to /boot/config.txt so that the aspect ratio of the HDMI screen exactly matches that of the TFT (320 x 240) - otherwise you'll get dead bands down the side of the TFT. This sets the HDMI output to 1280x960 which is the same aspect ratio as 320x240:

hdmi_group=2
hdmi_mode=32
hdmi_cvt 1280 960 60 1 0 0 0

This is when developing, so that with X running I still get a high resolution display for writing code etc., however, if all I am doing is running the Pi with JUST the TFT attached, then I use the following settings in /boot/config.txt which sets the default HDMI resolution to 320 x 240 BUT NOTE: my main HDMI monitor cannot display that resolution, so if I need to change it back, I have to edit /boot/confix.txt using the TFT display, which can be quite a challenge!

#hdmi_group=2
#hdmi_mode=32
hdmi_cvt 320 240 60 1 0 0 0

Once that is all done, and you've re-booted, start raspi2fb as a daemon by typing the following:

raspi2fb --daemon

And the HDMI should be mirrored to the TFT. The default framerate for raspi2fb is 10fps, so there is a bit of a lag between what happens on fb0 (HDMI output) and the mirrored version on fb1, but it is fine for my purposes. The important point is that I can then run RayLib as usual, and whatever I output to fb0 is automatically mirrored to fb1.

As I mentioned above, this actually gives me better performance than my raw graphics routines that wrote directly to fb1. I cannot really explain this, though I suspect that the Linux Copy On Write may have something to do with it??