gimp/docs/gpb.txt

Gimp Pixmap Brush File Format

The current format for gpb files, the pixmap
bnrush format is very simple. What it essentially
boils down to is a greyscale gbr (gimp brush) and
a rgb pat (gimp pattern) concatented into the same file.

The gbr is first, and is used for the greyscale mask for
the brush. The pat is second and is used for the rgb info in
the file.

The name and spacing info for the greyscale portion
is used for the name and spacing of the pixmap
brush.

The greyscale mask and the rgb data need to be of
the same height and width.

The easiest way to create a gpb file is to use the gpb plug-in.
Create an RGBA image, and save as a .gpb file.

(Before that plug-in was written, the easiest way to
create gpbs was:

	1. Create a rgb image of some sort. The best
	images seem to be something on a black background,
	but thats not required. 

	2. Generate a mask for all the parts of the image
	that should be transparent in the final product. There
	are several ways to do this but quickmask, or select
	by color, selection to channel seem to be a good way to 
	do it. This mask needs to be greyscale. So I usually
	make it a selection, and then use "save selection 
	as channel"

	3. Take that mask, select all, and cut it. Then
	open a new greyscale image, and paste it into the
	image. This is the easiest way to insure the images
	are the same size and are aligned. The white portions
	of this image will be what is opaque in the pixmap
	brush.
	
	 Take the above mask, and save it as a .gbr file. 
	It doesnt need to be in the brushes dir.

	5. Take the original rgb image, remove any mask layers,
	and flatten the image. Setting background color to black
	and flattening to a black background seems to work
	a little better. 

	Take this image, and save it as a .pat file. This does
	not need to be in the patterns directory.

	6. Go to a shell, and concatenate the files together
	into a .gpb. Ie, for a mask named foo.gbr, and a
	rgb pat name foo.pat:

		cat foo.gbr foo.pat > foo.gpb

	7. Copy that foo.gpb to your brushes dir
)


Adrian Likins
aug 18, 1999