I've been looking for a while but haven't found anything useful. When working with the perspective grid, the first thing I wanted to do is to draw a laptop. I wanted its lid to be slanted at an angle. I thought I could get away with just drawing two straight lines on different planes then connecting their ends, but then I couldn't figure out how to make a perfect round-cornered lid. Come to think of it, how do you even draw a foreshortened slanted circle on the perspective grid for that matter? Anything you draw snaps onto either the vertical planes, or the horizontal planes, and there are no slanted planes to help you with that. Other tools (rotate, shear, etc.) don't seem to work. Is it possible draw slanted objects at all?
No, the tool is useless* if you want any other angle than the ones given for you. You can on the other hand do it with the rotate effect, but due to not having a way to place the pivot and depth it is also not generally useful for making 3d objects, although it is far better.
* Well I would lean on the side that the entire tool is useless.