Show the Nintendo title animation when a Game Boy boots up (reference video) by simulating the boot process of a real Gameboy CPU and corresponding units, e.g. its PPU when a real boot rom and cartride is loaded.
I've reached the goal, i.e. this application is able to generate the single frames of the animation, leading to this beautiful gif
To enable this, I've implemented
- loading both boot and cartridge ROMS in Gameboy format
- simulating the Gameboy classic CPU including all necessary registers, flags and instructions to execute the original boot rom.
- handling video output by understanding and simulating the PPU (in a pragmatic way)
To keep this project small-ish, I've decided against adding a graphical library to show the results in realtime.
Instead, for every frame a single image is written (and stored in frames/). These frames can
be concatenated to create a gif using ImageMagick.
Note that the interpreter intentionally fails after the boot rom has successfully been interpreted and the animation has been played, i.e. stops at position 0x100 after generating the frames (which is expected).
Unknown opcode 0x00 at position 0x0100
PC=0100 SP=FFFE
A=01 B=00 C=13 D=00 E=D8 H=01 L=4D
Z1 N0 H0 C0
000000F0 f5 06 19 78 86 23 05 20 fb 86 20 fe 3e 01 e0 50 |...x.#. .. .>..P|
00000100 00 c3 50 01 ce ed 66 66 cc 0d 00 0b 03 73 00 83 |..P...ff.....s..|
00000110 00 0c 00 0d 00 08 11 1f 88 89 00 0e dc cc 6e e6 |..............n.|
This is a standard gradle project, i.e. you can build it via gradle build and generate the frames via gradle run. Once the frame have been generated, the animation can be created via
# brew install imagemagick
convert -delay 1x30 -loop 0 frames/logo-*.ppm logo.gif
Note that you need to have the files boot.gb (a Game Boy boot rom) and tetris.gb (an arbitrary Game Boy cartridge format) in the rom directory. For obvious reasons, these are not provided here.
Initially, I've abandoned the project before rendering the output because simulating the video processor (handling scanlines, etc.) seemed to be a daunting task. After having some new ideas I decided to take up the task again, leading to evenings where I spent my time looking at screens like the following:
Looking at the instructions of the boot rom and understanding what happens when a Game Boy boots up:
Looking at a running emulator to understand the memory layout of tile maps and video ram rendering:
In com.mlesniak.gameboy.CPU.showLogo, I've implement a method to interpret the boot rom logo data and show the
parsed logo.
00000000 31 fe ff af 21 ff 9f 32 cb 7c 20 fb 21 26 ff 0e |1...!..2.| .!&..|
00000010 11 3e 80 32 e2 0c 3e f3 e2 32 3e 77 77 3e fc e0 |.>.2..>..2>ww>..|
00000020 47 11 04 01 21 10 80 1a cd 95 00 cd 96 00 13 7b |G...!..........{|
00000030 fe 34 20 f3 11 d8 00 06 08 1a 13 22 23 05 20 f9 |.4 ........"#. .|
00000040 3e 19 ea 10 99 21 2f 99 0e 0c 3d 28 08 32 0d 20 |>....!/...=(.2. |
00000050 f9 2e 0f 18 f3 67 3e 64 57 e0 42 3e 91 e0 40 04 |.....g>dW.B>..@.|
00000060 1e 02 0e 0c f0 44 fe 90 20 fa 0d 20 f7 1d 20 f2 |.....D.. .. .. .|
00000070 0e 13 24 7c 1e 83 fe 62 28 06 1e c1 fe 64 20 06 |..$|...b(....d .|
00000080 7b e2 0c 3e 87 e2 f0 42 90 e0 42 15 20 d2 05 20 |{..>...B..B. .. |
00000090 4f 16 20 18 cb 4f 06 04 c5 cb 11 17 c1 cb 11 17 |O. ..O..........|
000000A0 05 20 f5 22 23 22 23 c9 ce ed 66 66 cc 0d 00 0b |. ."#"#...ff....|
000000B0 03 73 00 83 00 0c 00 0d 00 08 11 1f 88 89 00 0e |.s..............|
000000C0 dc cc 6e e6 dd dd d9 99 bb bb 67 63 6e 0e ec cc |..n.......gcn...|
000000D0 dd dc 99 9f bb b9 33 3e 3c 42 b9 a5 b9 a5 42 3c |......3><B....B<|
000000E0 21 04 01 11 a8 00 1a 13 be 20 fe 23 7d fe 34 20 |!........ .#}.4 |
000000F0 f5 06 19 78 86 23 05 20 fb 86 20 fe 3e 01 e0 50 |...x.#. .. .>..P|
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