If you use Raspberry Pi, please note the following with the 3.4.x releases:
With the 2D refactor, running in pure software mode simply is not playable on the Pi, anymore. However it will continue to be supported because running it on the VideoCore4 GPU chipset works, for now. Please note that Pi boards that are revisioned 2 or 3 are the only ones currently supported - you can run GZDoom on a Pi 1 but you must make some compile tweaks and it is not officially supported right now. (In other words - you're on your own!)
I should mention that none of this is officially supported by the Raspberry Pi Foundation as of yet - as is repeatedly said, "do this at your own risk" - the drivers for VC4 are still being perfected as of this writing. No one but you (not me, not the rest of the GZDoom team, not the Raspberry Pi foundation, not your distro's distributor, and not your seller) takes any responsibility, should anything go wrong if you follow these instructions.
To activate it - first, make a backup copy of your /boot/ folder and store it somewhere safe. This contains configuration settings as well as your current firmware.
Then, you must do the following (assuming you have a Debian variant - Raspbian has these tools pre-installed):
sudo apt-get install rpi-update raspi-config
Let the packages install, then run:
This will update the firmware (and the kernel) that you are currently running, and will install new drivers.
You must reboot. Then you can run:
This will allow you to configure hardware acceleration. Note that for now, I've only gotten "fake KMS" to work - use "full KMS" at your own risk!
You may be required to reconfigure your monitor or television's characteristics using "sudo nano /boot/config.txt" after doing these commands.
Be aware that running X11 with any acceleration at all is glitchy - but it is most definitely usable and errors are rarely fatal. (Most of the worst ones have been solved, even recently)
Note that 3.4.x will be the last mainline series that will run on the VideoCore4 chipset. More details will be coming in the future for alternatives that will be available.