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3. WinGrit v0.8.3

3.1. 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 GUI version.

Wingrit main view
Fig 3.1: Wingrit main view

3.2. Wingrit

The window that pops up first is basically an image viewer. Open any image and it is shown on the screen. You can zoom in and out with the scroll wheel and move it around with the middle mouse button. There are a few useful options in the menu like convertion to 16bpp, quantisation and also a palette viewer. The meat of the program is in the View window: the GBA Exporter. That's the big thing with all the buttons in fig 3.1.

There are 6 zones in the exporter:

  1. graphics
  2. map
  3. meta/object
  4. palette
  5. area
  6. file

And of course the main buttons in the lower left corner. There's also a summary window on the righthand side, which tells you a little about what and how the image will be exported.

The following is a list of options found on the dialog. The parts between parentheses are the corresponding command-line options.

3.2.1. Graphics

Fig 3.2: graphics options.

Graphics exporting options. Governs the actual graphics part of the data (i.e., the pixels). Affixes: “Tiles” or “Bitmap”.

  1. Enable box (-g[!]). Include (default) or exclude graphics in the output.
  2. Gfx format. The GBA has 2 basic graphic modes: tiled or bitmaps. The NDS has those too, but allows for bitmap transparency as well, which is why there are four modes here.
  3. Bit depth (-gB<n>). Usually, the bitdepths for GBA graphics are 4, 8 or 16 (for modes 3 and 5). 1 and 2 bpp are added for bit-packing. For example, a monochrome mode 3 font can be put in 1 bpp format instead of 16 bpp, for an effective compression of 94%. NDS textures can also be 2, 4, 8 and 16 bpp. If you're clever, you can use this for alpha-textures too.
  4. Graphics compression.
  5. Transparent color (-gT [hex]). For use with bitmap+alpha mode.

3.2.2. Map

Fig 3.3: mapping options.

Covers mapping (and some meta-mapping) options. Unlike palette and graphics, map data is excluded by default. For meta-mapping to work, you need: a) map data included and b) the tile-groupings should be larger than 1. Affix: “Map” (and maybe “MetaMap”).

  1. Enable box (-m[!]). Include or exclude (default) map (and meta-map) in the output.
  2. Map layout. The primary formats for GBA maps are regular (text) and affine (rotational), the former using 16bit screen entries and the latter 8bit. There is a second difference in that affine maps are ‘flat’ in memory, while the bigger regular maps are divided into separate screenblocks. This can make dealing with regular maps a tad annoying, because you may have to rearrange things to fit into the screenblocks.
  3. Tile reduction (-mR[tpf]). An image intended for tilemaps will often have duplicate tiles, which can be removed from the full tileset (i.e., the all the 8x8 tiles of the whole image). That's kind of the point of having tile-maps after all. This gives rise to a reduced tileset, which can be much smaller that the full set.
  4. NOTE: The reduced tileset always starts with an empty tile. As tile-0 is often ‘special’, I thought this'd be appropriate.
  5. Meta-tile palette reduction (-MRp). Normally, meta-tiling only looks at the full equality of the screen entries. This option allows further reduction based on the palette bank, which will be shared for the whole meta-tile.
  6. Map compression. I should probably point out that 8bit RLE is a very bad idea for regular maps, as the upper and lower bytes of the screen entries will rarely match.
  7. Tile offset (-ma <n>). For when you don't intend the tileset to be at the start of a charblock.

I would like to add more options here, like column-based maps, which should be easier to deal with for horizontal scrollers. But this will have to wait.

3.2.3. Metatile / Object size

Fig 3.4: Metatile options.

Tile grouping (-Mw<n> -Mh<n>). Grouping tiles can be done for two purposes. The first one is the obvious one to make sprite sheets work for linear sprite mode.

The second one is for meta-mapping – grouping multiple screen-entries (the meta-tiles) and using a map of those meta-tiles (the meta-map) instead of the full map. Depending on the size and variation of the metatiles, this can reduce the storage needed for the description of the entire map.

The Grit meta-tiling formatting works like this. If you export a (meta)map with the basename “foo”, then the map of the thing (fooMap is actually the metatile-set, which are composed of screen entries. The metamap is put in “fooMetaMap”. The entries of the metamap are 16bit, the lower 12 being the metatile index; the upper 4 the metatile palette bank, if applicable.

In order for metamapping to occur, map exporting must be on and the metatiles must be more than one tile in size.

  1. Fixed groupings. Corresponding to the standard GBA sprite sizes and shapes.
  2. Custom grouping. If you want groupings other than sprite sizes, toggle this and fill in the boxes.
  3. Custom group sizes. Width and height of tile groupings for custom mode. Note that the sizes are in units of tiles. Entering (8, 8) here would actually indicate 64x64 pixel tiles, for example.

3.2.4. Palette

Palette exporting options. Affix: “Pal”.

  1. Enable box (-p[!]). Include (default) or exclude palette in the output.
  2. start (-ps <n>). First entry of the full palette to export.
  3. num (-pn <n>). Number of palette entries to export. start and num form a subset of colors, [start, start+num). Range will be clamped to available palette at validation.
  4. Transparent index (-pT). Normally, index-0 is the transparent index in paletted images. This pick another one.

Fig 3.5:

Fig 3.6: area options.

3.2.5. Area

Lets you select the region of the image that you want to use. Most of the time this will probably be the whole image, in which case you can pretty much ignore this zone, but just in case you want only a portion, you can use this.

  1. Area options. Right now, this is just a switch between using the full image or a custom area. I did plan on using some kind of ‘selection’ tool and option, but I'll have to see whether anything ever comes of it.
  2. Area. Size of the rectangle you want to export. Note that the right-hand boxes are the sizes, and not the right and bottom sizes. You should probably also know that the final rectangle may change a little but due to the aligning requirement for (meta)tiling and sbb-map format.

3.2.6. File / symbol options

Fig [[ref:ig-xp-file]]: File options.

Various file and symbol name/type options.

  1. Destination path (-o <path>). Filename of where the data should go. If you don't want to type it in manually, there's a button to launch a file dialog on the right. The full path is (probably) not required, but can't hurt.
    The extension determines the file-type; if it's not recognized, it will default to a C file.
  2. File type. The extension will be based on this field, regardless of what you may have put into the path-field. Options are:
  3. Enable header file (-fh[!]). Creates a header file with declarations and a description of the data. This does NOT contain actual data! Data definitions in header files is bad, very bad, mkay? Mkay! Mkay. Apart from data declarations, it'll also hold size defines, the names of which are the data-names + “Len”.
  4. Append mode (-fa). Appends the data to the destination file, useful for keeping the number of files down. If data of that name exists already, it will be replaced. Binary files cannot use appending.
  5. riff (-fr). Enable GRF-format for non-grf files as well. Currently only for C and asm export. Note that this also forces off comrpession to off+hdr.
  6. Data-type (-U<n>). Arrays are in bytes, halfwords or words. Has no effect on binary or GBFS files.
  7. Base symbol name (-s <name>). The base-name part of the data arrays. If it's not a valid C name, the invalid parts will be replaced by underscores. The full names are created by adding the following affixes: “Pal”, “Tiles”, “Bitmap”, “Map”, “MetaMap”. For example, bitmap-data for the basename “foo” will be “fooBitmap”.
    By default, the basename is based on the path's title, but you can add a name manually too.
    NOTE. GBFS files use a 24 character name field. To make sure of distinguisable names, the basename will be truncated to a 21 character maximum, to which the affix is then added.
  8. External tileset. (-fx) With this, you can use an external tileset to map the bitmap to a tilemap. The combined tileset will be saved as well. This allows you to build up a shared tileset.
    NOTE: mapping must be enabled for this, and metamapping is not fully supported here yet.

3.3. Last changes

v0.8 (20080323)

v0.7 (20070414)

Modified Nov 29, 2008, J Vijn. Get grit here