I was fiddling around on OpenVG with my Rpi3, and I wanted to see if I could create a tiny ripple effect like on Android : starting from a tiny ellipse which grows up to fill out the entire screen.

I wanted it to be best looking than just a simple scaled ellipse, so I thought of using paths interpolation. When I interpolate an ellipse to another ellipse it works, but when I try to interpolate my tiny ellipse into the rect which fills up the screen it fails (vgInterpolatePath returns false).

I've read on the specification that for it to work, paths must be "compatible" : what does this mean ? Is there a way to interpolate an ellipse into a rect ?