I tried making a custom brush from an image, but when I did that a red X appeared in the brush designer and testing in the test panel only painted the color white.
Are there restrictions for brush images? Also, I saw mention of a stamping tool on the brush window, but I don’t see this.
At a higher level, my reason for wanting to do this is a simple way to do quick image edits where I’ve rotated an image but need it to fill in a specific aspect ratio. Cropping the rotated image while keeping the items you want, you’ll often have empty sections of the image. These can often by “fixed” by just extending what was in the background of the subjects.
You can use the clone tool to do this sort of thing, but I find the clone tool kind of irritating to use. I thought maybe just making a brush from a selection of the background, doing an initial fill with that, then touching up if needed would be a way to go about that. Does that sound reasonable or is that a dumb approach?
The red x is a button by Acorn to remove the image from the brush settings, and then to fall back to an auto-generated one. So it’s normal if you’re making a brush from an image.
As for painting in white- I’m assuming you’ve got the current brush color set to something other than white? Acorn 4 had a option to “colorize” brushes, but that’s the default setting now for Acorn 5 and 6.
The approach you’re using seems reasonable. One thing you might try and do is use Acorn 6’s new stamping functionality with the clone tool. So you could make a large brush, pick an area of your image you’d like to clone, and then on a new layer you could hold down the shift key while clicking to temporarily turn the clone tool into a stamp tool.
Both the functionality of cloning from a different layer, and the stamping are new in the Acorn 6 beta, which you can grab from here: Latest Builds from Flying Meat
You could also try copying + pasting in your image into a new layer, and erasing sections of the new layer that don’t look right.