Porting to other platforms

[RicoElectrico]

As a quick hack, I modified the library to get it working on the ESP-12F module. Have look at https://github.com/RicoElectrico/Arduino-SPI-LM15SGFNZ07-LCD-Library . This consisted of getting rid (for now) of progmem-related stuff and fixing the integer types. On the AVR sizeof(int)==2 unlike 4 on other platforms, including Xtensa.

I also encountered a nasty bug in the line drawing routine that may not have manifested itself on the AVR. In your version, one of the coordinates is unsigned instead of unsigned char which - if I read the stack trace correctly - messes with abs().

Great speed gain was achieved by upping the SPI clock. Unfortunately the Hyundai driver datasheet doesn't quote maximum clock period, having it "TBD". 35 MHz seems reliable on 30 cm of cabling.

Now that I proved it works, I have to find a way to use program memory again and make it into a single portable library with #defines. Writing a simple image converter using tiny no-dependence EasyBMP library would be a piece of cake, then.