It would like to be able to be able to make custom straight line and circular masks while painting in order to paint hard edges. The tool could work something like the selection tools in photoshop and while there is an area selected, all paint is constrained to that area.
Yes absolutely
yes yes a thousand times yes.
completely agree! you can achieve hard edges (or much closer) by increasing the brush hardness, just in case you weren’t aware. there’s no visual indicator but shift+] to increase, shift+[ to decrease.