Consider using LittlevGL for unlocker and charging screen
Currently encrypted partition unlocker osk-sdl and charging screen (charging-sdl) are using DirectFB and SDL libraries. DirectFB is no longer supported and requires additional configuration to get it working on mobile devices, usually working around problems with pixel modes. How about using an embedded GUI library LittlevGL instead? It is written in C, has low memory use and quite a few GUI widgets with themes support. It can draw directly to framebuffer and with small compiled file size we could fit unlocker and charging screen programs into initramfs. I have compiled a demo program and successfully ran it on semc-smultron device (with usual color issues), but I could not get touch input to work with provided evdev driver. Probably we'll need to create an input driver for tslib.