So it seems easy enough to create a static boot screen. But would it be possible to load an image and then display a progress spinner over the top?
What I'm thinking is reading the boot log messages somehow and every time a line appears the spinner updates until the login prompt is displayed at which point I want to exit the splash screen and run my application.
I can use that linked script as a base, but instead of running /usr/bin/fbi I could write a very small SDL application that loads the PNG and puts it on the screen. The problem is:
1) How do I peek at the boot messages?
2) How do I know when the boot is finished?