Added support for embedded portable handhelds

[kloptops]

Description

This PR is the changes required to allow GemRB to run on embedded portable handheld devices running linux.

The changes I have made are for the following purposes:

• These handhelds have limited hardware and as such require gles2 for rendering. The current shaders do not work, I have added a flag to disable GLSL shaders and this allows the game to run well. (-DUSE_NO_GLSL)
• The game is run with a companion program that listens to the handhelds gamepad and translates it into keyboard/mouse events, this allows more fine grained control and better portability between devices/platforms. GemRB currently listens for the same events and is doubling up events, i have added an option to disable the sdl controller api inside of gemrb. (-DSDL_DISABLE_CONTROLLER_API)
• The last option is to fix resolution independence on devices with higher resolution screens. These devices do not run with an x windows server so the current fullscreen/windowed code doesn't scale up the screen resolution. (-DSDL_RESOLUTION_INDEPENDANCE="ON")

Thank you so much for this excellent engine, we have a very active community and many people are excited to use this to play such classic games.

Checklist

• Commit messages are descriptive and explain the rationale for changes
• I used the same coding style as the surrounding code
• I have tested the proposed changes
• I extended the documentation, if necessary
• The proposed change builds also on our build bots (check after submission)

[lynxlynxlynx]

Thanks! Some cleanup will be needed, but first I want to check this odd GLSL stuff — did you actually load a game and saw it render well? I'm not sure you get much benefit from enabling a crippled GLES compared to the software rendering.

[kloptops]

Okay you're right, the GLSL stuff can be removed. I had issues with it when I was first getting the engine to run on the hardware. I ended up disabling the shader stuff then never tried it again.

Here is bg1 running on the hardware.

[MarcelHB]

Can you elaborate on what kind of devices you have been testing GemRB here? Like the SoC of that ... GameBoy? 😉 For future references and compatibility.

[kloptops]

So we have been testing it on the Anbernic RG351V (Rockchip RK3326), RG353V (Rockchip RK3566), and RG552 (Rockchip RK3399) on the AmberElec/ArkOS/UnofficialOS operating systems.

We use a system called PortMaster that allows us to package up the games in a way that they can run on all the above oses/hardware.

[lynxlynxlynx]

You can then add AmberElec / ArkOS /UnofficialOS to the exotic OSes list in the README as well.

[lynxlynxlynx]

Thanks!