This is the source code for the GBA Jam 2022 version
of Pocket Paint by Johnathan Roatch.

For copyright licensing information not defined in individual files see UNLICENSE.

That being said I highly recommend you *do not* use the whole project as
a "framework" to to start a new game from, but instead to read through
the code and maybe pick up a tidbit or two on how to do some things.​

If you happen to have A working instalation of `make`, `gcc`,
`arm-none-eabi-*`, and `lz4` ready to run from your system path,
then invoking `make` will build Pocket Paint.


## Thanks to

Jasper Vijn for his wonderful guide TONC https://www.coranac.com/tonc/text/toc.htm
gba_mem_def.h is a compilation of hardware names from TONC

The authors of PocketNES, Especialy for the "exiting to flash carts" routine

I think I also took the linker script `gba_mb.ld` from PocketNES as well,
but I forget.

Felix Jones for https://github.com/felixjones/agbabi making me aware for
the need of the set of `__aeabi_*` routines. I had planed to rewrite
those routines in my `gba_crt0.s` for the sake of "originaly"
but in the end that dosn't matter.

pinobatch for the Save/Load icons.

laqieer for https://github.com/laqieer/libsavgba
flash saving and loading code

https://github.com/Aikku93/ulcplayer-gba for giving me the idea to use a
de-Bruijn string to implement log2() to then use as the priority system of
the interrupt service routine.

incbin.h ​because including binary data is a non trivial task in C


## Special things that I did I would like to bring to attention

gba_crt0.s contains not only the startup and shutdown code, but also
the ARM embedded ABI routines that a C environment expects

The bootup order is
- Set GBA bus registers, including enableing all interrupts
- Start 16.78 Mhz Hardware timer to let run indefinitely
- Relocate from ROM to WRAM (using memcpy in ROM)
- Copy ARM routines (including __aeabi_*) to IWRAM (using memcpy in WRAM)
- populate SoftReset Flag, __isr_table, memset/memcpy C stuff (now using memcpy in IWRAM)
- start main

Exiting main will in order
- try exiting to flash cart
- failing that, Soft Reset to ROM if cart detected
- else Soft Reset to WRAM
additionally "Soft Reset" will execute the BIOS calls that simulates what
the hardware state is when the GBA logo plays out.

I have a VRAM 16-bit bus safe LZ4 decompression routine in `iwram_code.s`

The interrupt service routine passes a timestamp to called routines.
That same timestamp is used in get_system_clock() but note that it
needs IME to be disabled.

​The default 8-bit palette (unused) is from this conversation back in 2016
https://forums.nesdev.org/viewtopic.php?p=166952#p166952

I have a pixel ploting API that ​accommodates bitmap and
tilemap modes from 1bpp to 16bpp. I might in the future
have some routines to compute the byte pitches given a
discription of a tilemap

The cursor inverts based on a gamma adjusted blur of the pixels underneath.

The magnifying glass is all just palette colors