Any time that I have used automatic panning, it's always felt like a bad solution to the problem of the trade-off between view size and detail. It's clunky and unintuitive with how it essentially forces the mouse to move (relative to the screen), just because the mouse is in a specific area. Not to mention many times you go too far or its too slow, and because its purely based off of the mouse location, it can be hard to control.
I'm not exactly sure in what case you would want automatic panning for a standard brush, but even for the straight line tool, I feel it would just be better to allow a user to select the two points individually, without the need for dragging the mouse between the locations without letting it drop.
Yeah I can't imagine automatic panning being usable for a continuous stroke. I could see it if you're doing splines or something, and just need to get to an area of the canvas to click on.
I wonder if auto-zoom-out would be better than auto-pan. As you approach the edge, zoom out to give you more room. Then you're not just dragging blindly against a wall and ending up who knows where.
I'm not exactly sure in what case you would want automatic panning for a standard brush, but even for the straight line tool, I feel it would just be better to allow a user to select the two points individually, without the need for dragging the mouse between the locations without letting it drop.