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An object-oriented Gameboy Advance sprite engine concept
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README.md

A high-level object-oriented Gameboy Advance sprite engine library

Build Status

That's a mouthful - let's break that down:

High-level object-oriented

The GBA is an older piece of hardware that's missing an OS. While that is great (while(1) {}), it also means there's little software library support. GBA programming boils down to manipulating memory-mapped IO pointers. And that's not a lot of fun.

Instead of writing

vu16* paddle = ((volatile tile_block *)0x06000000)[0][1];
for(int i = 0; i < 4 * sizeof(tile_4bpp) / 2; i++) {
    paddle[i] = 0x2222;
}

Wouldn't it be a bit more readable if one could write

auto paddle = SpriteBuilder<Sprite>()
    .withData(paddleTile, sizeof(paddleTile))
    .withLocation(10, 10)
    .buildPtr();

To leverage C++11's abilities combined with a clear object-oriented approach using abstraction to hide the hexadecimal addresses? That's the objective of this engine.

Speed and size are NOT the primary concern! We value clean readable code above speedy algorithms. This is just a proof-of-concept, intricate games with a lot of data will never work because memory limitations. That said, feel free to fork and/or provide patches. The C++ cross-compiler and the GBA work, but create more metadata than the typical C cross-compiler. Take a look at the file size of the following binaries:

-rwxr-xr-x   1 staff    8320 Jul 25 13:54 main_c.gba
-rwxr-xr-x   1 staff   23328 Jul 22 20:36 main_cpp.gba
-rwxr-xr-x   1 staff   24032 Jul 25 13:55 main_cpp_stl.gba

The C++ ROM is 280% bigger than the C ROM, and if you include , even 288% bigger - from 8K to 23K! Emulating big files is not a problem, and running them on the actual hardware is still possible using cartridges like the EZ-FLASH Omega.

GBA sprite engine

That means MODE0.

library

It's compiled as a static library for your convenience. Simply link with the library and include the header path and you're all set. Take a look at the demo's CMake files if you're interested.

Engine features

A portion of ToncLib has been used as a low-level GBA accessor. If you know what you're doing, you can safely use those, headers are in <libgba-sprite-engine/gba>.

BIOS methods and Sin/Cos lookup tables are also compiled in Assembly, as sin_lut.

Design overview:

design

Colored blocks are to be implemented in your own game. See below, in section "implementing your game".

Implementing your own GBA Game

Scenes

Scenes contain sprites and backgrounds. You can transition between scenes with engine->setScene(scene) or engine->transitionToScene(scene, effect). The main program bootstraps your first scene - from there on it's each scene's responsibility to load another one.

This is the layout of a main function:

int main() {
    std::shared_ptr<GBAEngine> engine(new GBAEngine());

    auto startScene = new SampleStartScene(engine);
    engine->setScene(startScene);

    while (true) {
        engine->update();
    }

    return 0;
}

That's it!

To create your own scene, subclass Scene and implement:

  1. std::vector<Sprite *> sprites(): the sprites to load into VRAM
  2. std::vector<Background *> backgrounds(): your (multilayered) backgrounds
  3. void load(): one-time scene loading (create your objects here)
  4. void tick(u16 keys): gets called each engine update()
  5. set foregroundPalette and backgroundPalette in your load.

Loading up a scene usually involves creating some sprites with the builder. Don't forget to set the palettes like this: std::unique_ptr<ForegroundPaletteManager>(new ForegroundPaletteManager(sharedPal, sizeof(sharedPal)));

The sprites() method gets periodically called to check whether something has been added or deleted and updates the VRAM and OAM accordingly. You don't need to manage anything yourself! Take a look at demo 3.

A simple fade out scene effect is implemented in demo 1, that converges the palette colors of both palettes to white. It's easy to create your own effects by subclassing SceneEffect.

sample fade out

Sample fade effect, demo 1.

Backgrounds

Scrollable backgrounds are present:

Call scroll() in your scene update.

scroll bg

Sample scrolling background demo 1.

Creating a background:

    bg = std::unique_ptr<Background>(new Background(1, background_data, sizeof(background_data), map, sizeof(map)));
    bg->useMapScreenBlock(16);

Backgrounds work a bit different in VRAM compared to sprites. There are only 4 backgrounds available, and background #4 is taken by the font. Parameter 1 identifies your background used for prioritizing. Remember to use a screen block different than your map data.

Sprites

Conjuring sprites on the screen is a matter of exposing them to the sprites vector in your scene. Create them in your load and set them as a std::unique_ptr member variable in your scene so they get cleaned up automatically.

Creating sprites is easy with the SpriteBuilder. Specify what kind of sprite you want to make as a template argument (<Sprite> or <AffineSprite>) and speficy your data .with...(). Done? Call build() to get a copy or buildPtr() to get a copy wrapped in a unique pointer.

Affine sprites can transform using for example rotate(angle) - check out demo 1 or 3 for that.

rotation

Sample rotation demo 3.

Sprite animation is built-in! Just feed your sprite data to the builder and use .withAnimated(amountOfFrames, frameDelay). Remember to position each frame in one column in the image itself (vertically). Like this:

lama gif example

Useful sprite methods:

  • animate(), animateToFrame(x) or stopAnimating()
  • flipVertically(bool) or flipHorizontally(bool)
  • setVelocity(dx, dy) (auto-updates) or moveTo(x, y)
  • setWithinBounds(bool) automatically keeps your sprite within the GBA resolution bounds
  • collidesWith(otherSprite) or isOffScreen()
  • Various getters like getWith() etc

stay within bounds

The paddle auto-stays within bounds.

Each sprite has own raw data, so there's no shared sprite image (for the better). The palette of course is shared, so think about that when exporting with a tool like grit or png2gba. Grit has flags to export a shared palette:

grit pic1.png pic2.png kul.png -ftc -pS -gB8 -O shared.c

Consult the Grit list of cmdline options for more information.

Extracting a tilemap from a big image to create a splash-like intro screen can be done using these options:

grit splashimage.png -gt -gB8 -mRtpf -mLs -ftc

It will export:

  1. A tileset. Your data, to be injected into background VRAM char blocks.
  2. A tilemap. Your metadata, to be injected into the next free background VRAM screen block.
  3. A palette. Your one and only background palette.

Sound

The engine supports sounds and background music using GBA's Active Sound channel A and B. It's a simple implementation meaning no mixing in either channels (but A and B are mixed).

Call engine->enqueueMusic(data, sizeof(data)); as a repeating music or enqueueSound() as a one-timer. If some sound is already playing, it will not be played. Background music auto-repeats when done. See demo 1.

Sound can to be converted from a RAW Signed 8-bit PCM using raw2gba. Record something with for example Audacity and choose file -> export -> export audio... to change the format. Like sprite raw data, it'll be converted into a C header that you can feed to the methods above.

Text

default font

There's a default font embedded into the engine using the TextStream::instance() static instance. It takes up background #4 and claims the last background palette bank so watch out with that!

Useful text manipulation:

  • setText(txt, row, col)
  • << text or << int etc: append to text stream for debugging purposes.
  • setFontColor(COLOR): changes default color palette (white).
  • setFontStyle(const void* data, int size) if you prefer your own font face.

Changing the font style assumes a tile width of 32 and the same symbol indexes! It also resets the font color and map so call this before doing anything else.

Utilities

There's a game Timer class available using engine->getTimer(). It counts miliseconds, seconds, minutes and hours. Do not forget this is an estimate as modulo and divide operations are expensive.

Each VBlank occurs every 280806 cycles (CYCLES_PER_BLANK), each cycle is 59.59ns So, each VBlank occurs every 16.73322954 miliseconds or 16733.22954 microseconds. The microseconds after the comma are rounded so irregularities are bound to occur after hours of timing..

Error logging

The text stream is also used if something goes wrong, there's a macro failure_gba(WHOOPS) that prints file, line, method and "exception" message to the text stream background.

Unit Testing GBA games

The engine comes with (some) Google Test test cases to show you how separate classes can effectively be unit tested. I had to stub out some ARM-specific ToncLib includes, that's why the add_definitions(-DCODE_COMPILED_AS_PART_OF_TEST) CMake statement is there. Gtest compiles library source with g++ and not with the cross-compiler!

Compiling everything

Prerequirements

  1. cmake 3.12.x or higher: the cmake linker toolchain set contains a bug in .11
  2. A compiled Google Test 1.8.x or higher with $GTEST_DIR env. var
  3. The DevkitPro toolchain installed in your $PATH
  4. The mGBA emulator

Compiling with cmake

The project has been developed with CLion. The .idea dir is there for you to get started. The project can be imported as a cmake project.

As such, CMake was an easy choice. Use the following commands to build everything, including the demos:

  1. mkdir cmake-build-debug && cd cmake-build-debug
  2. cmake ./../
  3. make

The demos will be in cmake-build-debug/demox/demoname.gba.

Things you might need to change in CMakeLists.txt files:

  1. gba-sprite-engine assumes your GBA cross-compiler is in your $PATH. If it's not, add an absolute path to SET(CMAKE_C_COMPILER arm-none-eabi-gcc) etc.
  2. gba-sprite-engine assumes your Google Test Library is compiled and in your $GTEST_DIR path. If not, add an absolute path to: SET(GTEST_LIBRARY "/Users/jefklak/CLionProjects/googletest-release-1.8.0/googletest"). The linker searches for 'ligbtest.a' and 'liggtest_main.a' - if you're on Linux it'll likely be a .so extension.
Building using Windows

Tested ander working under Windows 10. Use MinGW or Cygwin, and add the -G "Unix Makefiles" option to your cmake ./../ command.

Cygwin is also a possibility, but combined with CLion the Unix and Windows path structures will clash. If using an IDE like CLion, resort to using MinGW.

Running unit tests

After compiling, execute the unittest main executable:

./cmake-build-debug/test/unittest

And hope for exit code 0!

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