This one is pretty simple to explain, since it exists in other software as an example,
Basically a layer setting that automatically adds an outline as a post-effect. (single pixel, unlike above). It is a post effect, so erasing also automatically adjusts in a non destructive way.
I’d love to see an outline setting that lets you set the thickness.
The current outline option isn’t often useful because it’s destructive. Automatic, non-destructive outlines like this enable some cool time-saving techniques too.
Really, layer styles and modes in general would be great to have. Outlines, alpha locking as a layer property so it can be mixed with other inks, glows, drop shadows…
To me, the big thing with auto outlines is that it would remove the guesswork when drawing flats, since it would show you exactly how “thick” the sprite is with outlines rather than guessing. Since drawing with lines is usually a bit messy or requires cleanup.
Currently you can press Shift+O to preview outline. But it is not really friendly as you will have to switch to right color each time.
I know it’s not the most ideal, and may not fully address this, but while I too was trying to find a nice solution, I couldn’t find anything, so I made scripts to create these outlines on demand:
(Sorry to respond to this a million years later, just chiming in since I still hope this gets added eventually)
Unfortunately it doesn’t accomplish the main goal, which is that being able to see the outlines as you draw. The problem is that people tend to draw the sprite as it looks good with flats, and so when outline are added after, it can result in the sprite being too “thick”, and the lines and sprite need to be adjusted. (for example head is all wrong, here.)
By having real-time outlines, it would allow you to see the result of the outlines as you are drawing, which would allow you to fix these issues as they come. Since probably 50% of the pixel art out there has outlines in one way or another, real time outlines would be a pretty big deal in terms of efficiency.