This is a very simple but fun effect that can be
achieved in just a couple of lines of assembly. This
effect is done using the same Nintendo logo that is
left on VRAM by the boot rom. In our program we
change the horizontal and vertical scroll for each
scan line of the LCD using a lookup table. For this,
we only need a toolchain that outputs instructions
for the Sharp LR35902 CPU. RGBDS
(https://rednex.github.io/rgbds/) will be our
weapon of choice. It includes an assembler, linker
and rom header fixer.
For compiling this with RBGDS we use the
following commands:
rgbasm -o wobble.o wobble.asm
rgblink -o wobble.gb wobble.o
rgbfix -v -p0 wobble.gb
Now that the rom is built we can run it on the BGB
emulator or a physical system. Sadly it wonβt work
with a Game Boy Color because that system clears
the logo from VRAM after booting up.