Infinite painter shows the major and minor axis of ellipses when editing the shape and puts the handles for adjusting the ellipse exactly on those axis as well as in the middle, that way you can place and transform the ellipse accurately. Improvement: The shape tool shows the mid point and both axis of the ellipse, but it disappears after the shape is finished, sometimes though it is necessary to draw these things for further construction, so an option to toggle that on or off to keep it after the shape is finished would save time.
All The shapes can be duplicated with just a tap on the clone icon and The new shape can be adjusted immediately afterwards. Improvement: after duplicating the shape you usually want to move it, infinite painter does not use snapping horizontally or vertically, but that would be very useful, for example when drawing a vertical cylinder, where you draw a circle, clone it and move it Up or down along the vertical mid point.
While the ellipse tool snaps to a perfect circle, the rectangle tool does not snap to a perfect square and does not show dividing lines like the ellipse tool, that its missing in infinite painter. Also missing (procreate has some of it) is the option to change the type of shape for the times where the tool does not recognize the shape correctly, like turning into an arc (half of a sphere) when you tried to draw a curve with multiple points.
What’s great about the curve is that you can add and remove more points as needed And also make the points Shape or curved by tapping on them. Works like a vector pen tool.
When using the shape tools together with perspective guide, they also snap to the perspective grid. This is super helpful. I am sure I forgot a few good functions, you should just play with them in infinite painter for a few minutes and get inspiration for how to implement something like that