Prev Contents Next

Grit v0.8.4

1.1. Introduction

The GBA Image Transmogrifier (“grit” for short) is a bitmap conversion tool for GBA/NDS development. It accepts a multitude of file types (bmp, pcx, png, gif, etc) at any bitdepth and can convert them to palette, graphics and/or map data that can be used directly in GBA code. The output formats are C/asm arrays, raw binary files GBFS files, and a RIFF-format I call GRF. The data can be compressed to fit the BIOS decompression routines.

Grit can do more than simply turn bitmap into arrays. It allows you to crop or enlarge the original work area, convert between bitdepths, break the images up into tiles or metatiles and supports NDS bitmaps with transparency. It also has a number of tile-mapping options: it can take the bitmap and turn it into a tilemap (and metamap) and a set of unique tiles. It can also merge the palettes or tilesets from multiple files.

If you need more, feel free to add your own code. This is an open-source project and the code should compile on all platforms, though you'll have to write your own makefiles for non-Windows environments.


Grit comes in two flavors: a command-line version, grit, and a Windows GUI, wingrit. This is the documentation for the command-line version.

1.2. List of options

1.2.1.. Graphics options

-g
Include graphics in output.
-g!
Exclude graphics from output.
-gb
Bitmapped graphics output. NOTE: without an -gT option, this data will have a clear bit 15.
-gt
Tiled graphics output (default).
-ga <n>
Pixel offset for non-zero pixels. Useful if the associated palette is at an offset.
-gB <n>
Bit depth of the output. Can be 1, 2, 4, 8 or 16. 16 bpp is a truecolor mode, the rest are paletted. If the source image is not of this bitdepth yet, it will be converted.
-gS
Shared graphics. Build up a shared tileset for the multiple images. See also -fx, -S and -O.
-gT [ <h> ]
Transparent color. The color should be a 16bit BGR color or 24bit RGB color in hex. For truecolor output, all pixels will have the alpha-bit set except this color. For paletted output, this color will be transferred into index 0.
-gT!
No transparent pixels / set the alpha-bit of the pixels. Only has effect for NDS bitmaps.
-gu8
Graphics data is in byte arrays.
-gu16
Graphics data is in halfword arrays.
-gu32
Graphics data is in word arrays (default).
-gz!
Graphics data is not compressed. (default)
-gz0
As -gz!, but with a compression header. byte 0: 0x00, bytes 1-3: size of data.
-gzh
Graphics data is 8-bit Huffman compressed.
-gzl
Graphics data is LZ77 compressed.
-gzr
Graphics data is RLE compressed.

1.2.2. Area options

-ab <n>
Bottom side of the work bitmap's rectangle. If this falls outside of the source bitmap, the latter will be extended.
-ah <n>
Height side of the work bitmap's rectangle. If this makes the bottom fall outside of the source bitmap, the latter will be extended.
-al <n>
Left side of the work bitmap's rectangle. If this falls outside of the source bitmap, the latter will be extended.
-ar <n>
Right side of the work bitmap's rectangle. If this falls outside of the source bitmap, the latter will be extended.
-at <n>
Top side of the work bitmap's rectangle. If this falls outside of the source bitmap, the latter will be extended.
-aw <n>
Width of the work bitmap's rectangle. If this makes the right side fall outside of the source bitmap, the latter will be extended.

1.2.3. Map options

-m
Include map in output. Enables tile-mapping of the image.
-m!
Exclude map from output (default).
-ma <n>
Tile index offset (non-zero indices only). Useful if you intend to load the tiles at an offset.
-mB...
Custom mapsel (map('s?) element) bitformat. The regexp format for it is "-mB((\d+):)([iphv_]\d*)+", that is, "-mB", followed by the bitdepth of the mapsel, a colon and a character-number pattern indicating the big-endian order and size of the bitfields. Available fields and their indicators: For example, the Text-BG mapsel format is: "16:p4vhi10".
-mLa
Map layout for affine tilemaps: 8-bit screen entries and a flat map.
-mLf
Map layout for regular backgrounds. 16-bit entries, but a flat map (i.e., not broken down into screenblocks).
-mLs
Map layout for regular backgrounds. 16-bit entries, broken down into screenblocks.
-mp <n>
Forces the palette-bank index to n.
-mR!
Disable tile reduction for tilemaps.
-mR4
Tile reduction combo for regular backgrounds with 4bpp tiles: tile, palette and flip reduction.
-mR8
Tile reduction combo for regular backgrounds with 8bpp tiles: tile and flip reduction.
-mRa
Tile reduction combo for affine backgrounds: tile reduction only.
-mRf
Tile reduction option: reduce for flipped tiles. Can be combined with t and p reduction options (example: -mRtpf).
-mRp
Tile reduction option: reduce for 16-color palette banks. Can be combined with t and f reduction options (example: -mRtpf). Do not use this for 8bpp tiles – you'll regret it.
-mRt
Tile reduction option: reduce for unique tiles. Can be combined with p and f reduction options (example: -mRtpf).
-mu8
Map data is in byte arrays.
-mu16
Map data is in halfword arrays (default).
-mu32
Map data is in word arrays.
-mz!
Map data is not compressed. (default)
-mz0
As -mz!, but with a compression header. byte 0: 0x00, bytes 1-3: size of data.
-mzh
Map data is 8-bit Huffman compressed.
-mzl
Map data is LZ77 compressed.
-mzr
Map data is RLE compressed.

1.2.4. Metamap/object options

-Mh
Metatile height. Useful for keeping the tiles in a metatile/object together. If tile-mapping is enabled, this will enable metamapping. Works together with -Mw.
-Mw
Metatile width. Useful for keeping the tiles in a metatile/object together. If tile-mapping is enabled, this will enable metamapping. Works together with -Mh.
-MRp
Metatile palette reduction.

1.2.5. Palette options

-p
Include palette in output (default).
-p!
Exclude palette from output.
-pe <n>
End' palette entry. For example, -pe 32 would output the palette up to, but not including, color 32. Works together with -ps.
-pn <n>
Number of palette entries. Works together with -ps; overrules -pe.
-ps <n>
Starting palette entry. -ps 16 would start the export at color 16. Works together with -pe and -pn.
-pS
Shared palette data. The colors of the source bitmaps are merged into a single palette. See also -O and -S. NOTE: will alter the order of the original palette (unless the first bitmap happened to have all the colors in it (hint, hint)).
-pT <n>
Transparent palette index. Only works if the input or output is paletted. For paletted output, it'll swap the transparent index with index 0 so that that becomes the transparent index. For paletted → truecolor conversion, the color of the transparent index will be used for transparency, working as a -gT option.
-pu8
Palette data is in byte arrays.
-pu16
Palette data is in halfword arrays (default).
-pu32
Palette data is in word arrays.
-pz!
Palette data is not compressed. (default)
-pz0
As -pz!, but with a compression header. byte 0: 0x00, bytes 1-3: size of data.
-pzh
Palette data is 8-bit Huffman compressed.
-pzl
Palette data is LZ77 compressed.
-pzr
Palette data is RLE compressed.

1.2.6. Input/output options

-fa
Append to output file instead of overwriting. If data with the symbol name already exists in the file, it will be replaced. Has no effect for binary output.
-ff <path>
Flag file for additional options. Instead of adding all the options to the makefile, you can use an external file to store and modify them.
-fh
Create header file with declarations and array length definitions (using array-name + Len).
-fh!
Do not create header file with declarations.
-fr
Group the separate arrays into a GRF-formatted array. See also -ftr.
-ftb
Export to binary files. Each array will have its own file: palettes will go into *.pal.bin; graphics data into *.img.bin; map data into *.map.bin; metamap data into *.meta.bin.
-ftc
Export to C arrays.
-ftg
Export to PinEight GBFS format. Note that the GBFS entry names are limited to 24 characters, 6 of which are already used for data affixes.
-ftr
Export to GRF (Grit RIFF). See notes for details.
-fts
Export to GNU assembly arrays. Default output filetype.
-fx <path>
External tileset bitmap which can then be shared between different tilemaps. Implies -gS. NOTE. This is still a little fickle. The file must already be in the correct format: a column or reduced tiles with 8bpp. If the file-type does not support 8bpp, a .bmp of the same name will be used. -fx works a little differently in v0.8 than before. See info:shared for details.
-o <path>
Output file path.
-O <path>
Output file path for shared data.
-s <name>
Base name for array symbols. Invalid identifier characters will be replaced by underscores. If this option is not given, then the name follows from the output title, or from the input title if -fa is given.
-S <path>
Base name for symbols for shared data.

1.2.7. Misc options

-tc
Tiling is done in column-major order, instead of row-major. This can be useful for horizontal scrollers, or efficient tile rendering.
-th <n>
Set height of basic tile (default: 8).
-tw <n>
Set width of basic tile (default: 8).
-U8
Set all output to use byte arrays.
-U16
Set all output to use halfword arrays.
-U32
Set all output to use word arrays.
-Z!
Set all output to use no compression.
-Z0
As -Z!, but with a compression header. byte 0: 0x00, bytes 1-3: size of data.
-Zh
Set all output to use 8-bit Huffman compression.
-Zl
Set all output to use LZ77 compression.
-Zr
Set all output to use RLE compression.
-W1
Log error messages.
-W2
Log errors and warning messages.
-W3
Log error, warning and status messages. There are a lot of status messages, so this is mainly for debugging.
-We
See -W1.
-Ws
See -W2.
-Ww
See -W3.

1.3. DWIM

For those who don't know, “DWIM” stands for “Do What I mean”, in the sense that grit attempts to guess at options that aren't specified explicitly, or correct for options that conflict, rather than quite and yell at you. In principle, this can be considered a Good Thing, but it does make it harder to predict exactly what will happen at times.

The list here covers the various defaults and overrides that Grit uses. I'll try to make it as complete and accurate as possible, but it sometimes gets so convoluted that even I don't know anymore ^_^;;. If you find something that's wring or missing here, please let me know.

1.3.1. Default settings

1.3.2. Overrides

1.4. Examples

[[TODO]]

1.5. Additional information

1.5.1. GRF files

I made myself a RIFF binary format because a) different loose binaries are somewhat annoying and b) they lose all context. A RIFF chunk looks like this: 

struct chunk_t {
    char id[4];
    u32  size;
    u8   data[1];
};

A 4-byte identifier, a 4-byte size field, indicating the size of the data (not the size of the whole chunk!) and a variable-length data array. A GRF chunk (pronounced “griff”) will look like this: 

"RIFF" # {
    "GRF " # {
        "HDR " # { header info }
        "GFX " # { gfx data }
        "MAP " # { map data }
        "MTIL" # { metatile data }
        "MMAP" # { metamap data }
        "PAL " # { palette data }
    }
}

The names are the (sub-)chunk identifiers, '#'s the size field, and the accolades indicate the data arrays. Each of the chunks inside "GRF " is actually optional, with the exception of the header. What goes into the header is still tentative, but for now it looks like this: 

struct GrfHeader
{
    u8  gfxAttr, mapAttr, mmapAttr, palAttr;
    u8  tileWidth, tileHeight;
    u8  metaWidth, metaHeight;
    u32 gfxWidth, gfxHeight;
};

The attributes here are just the bitdepths for now, or 0 if the the item isn't exported, but this behaviour may change later. The tileWidth and tileHeight are the tile dimensions in pixels, and metaWidth/Height are the metatile dimensions in tile-units.

GrfHeader is unfinished

I'm still considering what should go into the header here; things like map/metamap sizes may be useful, as would offsets, formats and other niceties. These may be added at a later date.

The following is a simple reader for GRF-formatted data. 

#define CHUNK_ID(a,b,c,d)   ((u32)( (a) | (b)<<8 | (c)<<16 | (d)<<24 ))
#define ID_RIFF             CHUNK_ID('R','I','F','F')
#define ID_GRF              CHUNK_ID('G','R','F',' ')

//! Decompress a GRF item.
bool grf_decomp(const void *src, void *dst)
{
    if(src==NULL || dst==NULL)
        return false;

    u32 header= *(u32*)src;
    uint size= header>>8;
    
    switch(header & 0xF0)
    {
    case 0x00:      // No compression
        tonccpy(dst, (u8*)src+4, size);     return true;
    case 0x10:      // LZ77
        LZ77UnCompVram(src, dst);           return true;
    case 0x20:      // Huffman
        HuffUnComp(src, dst);               return true;
    case 0x30:      // RLE
        RLUnCompVram(src, dst);             return true;
    default:
        return false;
    }
}

//! Load grf data
bool grf_load(const void *src, void *gfxDst, void *mapDst, void *palDst)
{
    u32 *src32= (u32*)src, id;
    
    // Must start with "RIFF" - "GRF "
    if(src==NULL || src32[0] != ID_RIFF || src32[2] != ID_GRF)
        return false;
    
    uint sizeMax= src32[1]-4;   // GRF size
    src32 += 3;                 // Skip GRF ID and size

    uint i, size;
    for(i=0; i<sizeMax; i += size+8)
    {
        id= src32[0];
        size= src32[1];
        switch(id)
        {
        case CHUNK_ID('G','F','X',' '):
            grf_decomp(&src32[2], gfxDst);  break;

        case CHUNK_ID('M', 'A','P',' '):
            grf_decomp(&src32[2], mapDst);  break;
            
        case CHUNK_ID('P','A','L',' '):
            grf_decomp(&src32[2], palDst);  break;
        }
        src32 += (size+8)/4;
    }

    return true;
}

Note that the header and metamap chunks are ignored here for simplicity's sake. Also note the decompression routine. I've made it a requirement that each item must have a header word compatible with the BIOS functions, even if there is no actual compression (hence the difference between -Z0 vs -Z!). That way you can get the compression-type from the data itself, even if there's no actual compression. Another requirement is that each chunk must be word-aligned. This is actually part of the IFF-spec itself.

There is a reference to tonccpy() in grf_decomp(). This is a memcpy() replacement that also works properly for GBA-VRAM. You can get it from coranac:tonccpy, or you can just replace the call with memcpy() or any other copy routine if you're sure you won't run into trouble with those.

You can export to GRF using -ftr. You can also get GRF arrays by using -fr, but that presently only works for C and asm data. The extension used for the arrays there is “Grf”.

GRF bug!

There was a small inconsistency between the GRF format and the way IFF chunks were supposed to be laid out. I had an additional size field after the chunk-title (like “GRF ”) which should not have been there.

Thank you, Daniel Hyde for pointing this out.

1.5.2. Shared data

In previous versions, you could have build up shared tileset with the -fx option. This would add new tiles to the tileset if they couldn't be found and save it to a bitmap. This worked, but because the runs were still essentially singular you ended up with intermediary palettes and tilesets unless you took steps to prevent it. And you had to export the tileset separately afterwards.

As of v0.8 this is now different. If …

  1. you have multiple source files, and
  2. -gS, -pS or -fx is set

… grit will exclude the temporary palette and/or tileset (whatever is appropriate) from the individual parts and only export the completed sets at the end. The name of the shared data can be controlled with -S and that of the shared output file with -O (uppercase for shared, versus lowercase for individual). If you don't add these names, they will be taken from the lowercase versions; if those are absent too, the name of the first source file will be used as a basis.

1.5.3. Todo list

Here are a few things that I'd like to add at some point. If anyone want to help flesh it out, that'd be great.

1.5.4. Last changes

v0.8.4 (20100204)

v0.8.3 (20081207)

v0.8.2 (20081129)

v0.8 (20080212)

v0.7 (20070414)

v0.7b (20070317)

The batchrun and external tilefile support is still experimental. YHBW.


Modified Nov 29, 2008, J Vijn. Get grit here
Prev Contents Next
Index Grit in projects