JNesG documentation

Introduction

JNesG is a Nintendo Entertainment System Graphics editor program. It was designed specifically for the NES, and can not support any other system. It is ideal for both NES developers and ROM hackers. It is a new program and so it still has some refining to do, and likely has many bugs lurking beneath, check the readme for info on those kinds of things.

Prerequisites

You need to be familiar with how the NES handles graphics: CHR Blocks, Name Tables, palettes, etc. If you're familiar with that, you'll probably be fine just playing with it for a while. Otherwise, read on.

Creating your palette

Just drag the desired color from the master palette over to your user palette. If you drag to a mirrored entry, it will mirror itself across all mirror entries. To create a new palette click "new".

Drawing Tiles

Just pick a color and start drawing, pretty standard stuff. If you're confused on why sometimes you get an unexpected color, see below.

To the right of the drawing area is the preview, which shows the tile at 2x zoom. Once you are satisfied with your tile click and drag the preview into a spot in the chr block, wherever you want.

CHR Blocks

Not much here, to make a new block click "new", to clear out a block click "clear". The white bar just divides between sprite and background tiles, which half is which is up to you.

Name Tables

Name Tables are handled just like tiles except their "palette" is the current active CHR block. Name Tables are either "low" or "high", which indicates which half of the CHR Block they get their tiles from. Switching between the two doesn't hurt anything, your Name Table will just get redrawn with the other half's tiles (try it to see what I mean).

Importing

From iNES ROMs

Just select "File > Import > from iNES ROM" from the menu or click the little import button that has a tiny NES cart on it, then pick the NES rom you want. All of the CHR roms from that ROM will be placed into the CHR Manager.

JNesG is not capable of importing palettes or name tables. So when you import from an iNES ROM, JNesG creates a "reasonable" palette that has four high contrasting colors to make it easy to see the tiles, otherwise a palette of all black would make it look like the import failed.

From Binary Files

Palettes, Name Tables and CHR Blocks can be imported from raw binary files that contain only the relevant data. JNesG will try to import as many valid components from these files as possible, but will reject anything that's not legal. For example if you give JNesG a file to be imported as palettes, each 16 byte chunk will be made into a palette, as long as each byte is between 0 and 63, any excess bytes will be ignored. Any invalid entry (negative or greater than 63) will result in zero for that color. Similiar things happen for CHR blocks and name tables.

To do this, just select "File > Import > from Binary" from the menu or click the little import button, choose your files, and click "import".

Exporting

to an iNES ROM

Just select "File > Export > to iNES ROM" from the menu or click the export button with the little NES cart on it. Then select the ROM you want to export into. JNesG will attempt to export all CHR blocks into a copy of the ROM.

As many CHR blocks as can fit into the ROM will get exported. If not all can fit, then some won't make it and JNesG will let you know. If there's too much space then all CHR blocks will get exported and the remaining blocks left alone. It's generally best to export your blocks into a ROM that has exactly that many blocks, and even better still to export blocks into the same ROM you imported from.

This exporting takes place in a copy of the ROM, which will be named <original name>_exported.nes, and in the same directory as the original.

to raw binaries

This is generally the way to go when creating your graphics for your own NES project. Select "File > Export > to Binary" from the main menu, or click the export button. A dialog will appear to set how to do the export.

What should be exported: Just check what you want to export

Save each type to multiple files: This may not be what you think it is. Palettes, CHR blocks and name tables are always exported into their own files. This option determines whether to put all palettes into one file or split each one off into their own files, which will be of the form mygame_pal0.bin, mygame_pal1.bin, mygame_pal2.bin, etc. It's not possible to export everything into one file, however you can just use JNesG's internal save format if you want (see below).

Other things

Unexpected colors when drawing tiles...
A little investigating should make it obvious why, and remember this is a graphics program specifically made for the NES. A tile can only have the values 0 through 3, but there's 16 colors in the palette. So the palette is split into 4 subpalettes, and which ever subpalette is selected (the two bit binary buttons above the palette, which is not implemented just yet) determines which subpalette is used to draw the tile at any given moment. Despite one subpalette always being the selected one, you can select any color in the palette to draw with. I haven't bothered to change that. The tiles will get saved to disk as just being arrays of numbers between 0 and 3, the colors are only there for your reference and don't really matter, as a sprite's "subpalette" must get determined elsewhere in an NES game. Read Yoshi's NES doc or Marat's NES doc for more information.

Attribute tables...
There's a lot of things I'd like to put into JNesG, and will eventually. Attribute tables are coming. See the readme in the distribution for a list of "todo's".

Loading another master palette...
In future versions, this will probably be doable. If you really want to change it now, it's actually not that hard, just requires a recompile. In the source (which, if you don't have, can be had from my website), head to jnesg/palette/MasterPalette.java. Scroll down a bit and you'll see a huge array literal full of PaletteEntry objects, the hex triplets in each constructor is the rgb value for that palette entry. Change as you like, and recompile (use ant, the source has a build file).