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https://github.com/exelotl/trick

Library for GBA/NDS image conversion, and more!
https://github.com/exelotl/trick

gameboy-advance gba nim

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Library for GBA/NDS image conversion, and more!

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README 

        
## Trick ;)



- [API Documentation](https://exelotl.github.io/trick/trick.html)



Trick is a library for GBA and NDS asset conversion in Nim.



It is used by the [Natu](https://github.com/exelotl/natu) project tool, providing an easy way to put images & maps into your GBA games.



It was also used for the [PP20th translation](https://www.romhacking.net/translations/4522/) project, thus is able to convert binary data back to PNG in some cases.



## Features



- Sprite Graphics

  - Convert PNG images to raw GBA image data, and vice-versa

  - Supported formats: 2 / 4 / 8 bpp paletted images using 15-bit BGR color, with bitmap or tile arrangement

- Backgrounds / Tilemaps

  - Convert PNG images to a map + tileset + palette.

  - Tileset reduction: identify & remove duplicate tiles, including flipped versions

  - Rearrange maps into screenblocks

- Palette Reduction

  - Given a list of palettes, attempt to merge them into the least number of 16-color palettes necessary. This doesn't produce optimal results, but may be good enough for some projects.

- Data Utils

  - Facilities to reinterpret data as an array of some known type, without copying

  - Convert raw bytes to C strings (a utility borrowed from the Nim compiler)

  - Name helpers: filename to identifier, snake_case to camelCase



## Overview



Trick is intended to allow you to make your own command-line tools to wrangle assets for your homebrew projects.



### Installation



```

$ nimble install trick

```



## Examples



These examples use hardcoded settings and paths, but in practise you'll want to be looping over directories, reading from config files, etc.



### PNG to binary



Convert your sprite sheets into raw binary formats used by GBA/NDS games:



```nim

import trick



var conf = GfxInfo(

  pal: @[clrEmpty],   # initial palette

  bpp: gfx4bpp,       # bit depth

  layout: gfxTiles,   # arrange into 8x8 tiles

)



# do the conversion

# `data` is now a string containing raw pixel data

# `conf.pal` will be populated with all the colors in the image

let data = pngToBin("mario.png", conf, buildPal=true)



# output to files

writeFile("mario.img.bin", data)

writePal("mario.pal.bin", conf.pal)

```



### Binary to PNG



The inverse of the above process. This may be useful for rom hacking, validation etc.



```nim

let conf = GfxInfo(

  pal: readPal("mario.pal.bin"),

  bpp: gfx4bpp,       # bit depth

  layout: gfxTiles,   # unscramble from tile arrangement

)

let data = readFile("mario.img.bin")

let png = binToPng(data, conf)

writeFile("mario_out.png", png)

```



### PNG to tileset + tilemap + palettes



The typical use case here is to take an image of your whole level and transform it into a tile map. Under the hood this involves both tileset reduction and palette reduction.



```nim

let bg4 = loadBg4("brinstar.png")

writeFile("brinstar.map.bin", toBytes(bg4.map))

writeFile("brinstar.img.bin", toBytes(bg4.img))

writeFile("brinstar.pal.bin", toBytes(joinPalettes(bg4.pals)))

```



### Data to C



While the above examples use `.bin` files, the preferred way to embed read-only data in your Nim GBA games is by using extenal C files. 



Example:



```nim

let data = readFile("mario.img.bin")



# convert binary data to a C string literal

let imgStringLit = makeCString(data)



# output C source code

writeFile("source/gfxdata.c", fmt"""

const char *marioImg = {imgStringLit};

""")



# output Nim source code

writeFile("source/gfxdata.nim", fmt"""

{{.compile: "gfxdata.c".}}

var marioImg* {{.importc, extern:"marioImg", codegenDecl:"extern const $# $#".}}: array[{data.len}, uint8]

""")

```



To explain the generated Nim code: the [`{.compile.}`][1] pragma ensures that `gfxdata.c` is compiled and linked into the final ROM. The [`{.importc.}`][2] and [`{.extern.}`][3] pragmas are used to make the C variable accessible to Nim. [`{.codegenDecl.}`][4] is just to help avoid compiler warnings.



It's worth mentioning that this Nim code *could* be written by hand, but I recommend this approach to maintain integrity between the assets and the game code. It will also save a lot of work once you modify your tool to support multiple images, by using a config file or by processing all images in a certain folder, etc.



[1]: https://nim-lang.org/docs/manual.html#implementation-specific-pragmas-compile-pragma

[2]: https://nim-lang.org/docs/manual.html#foreign-function-interface-importc-pragma

[3]: https://nim-lang.org/docs/manual.html#foreign-function-interface-extern-pragma

[4]: https://nim-lang.org/docs/manual.html#implementation-specific-pragmas-codegendecl-pragma



Example of using data in your game code:



```nim

import natu, gfxdata



# copy the image data into VRAM

memcpy32(addr tileMemObj[0], addr marioImg, marioImg.len div sizeof(uint32))

```



---



## Todo



- Fonts (currently the only way to produce [TTE](https://www.coranac.com/tonc/text/tte.htm) compatible fonts is [Usenti](http://www.coranac.com/projects/usenti/))



- ASM output?



- Ability to convert backgrounds/tilemaps back into PNG



- More graphic formats (in particular, NDS 3D texture formats with alpha bits have been implemented by [MyLegGuy](https://github.com/MyLegGuy) for PP20th, but I've yet to merge this code)



- Metatiles?