SDL_MULTIGESTURE usage and pinch / expand detection

Hi,

documentation on SDL_MultiGestureEvent is -lets call it- “lacking”. Can someone explain the meaning of: dTheta, dDist, x, y fields?

Docs just say “description” for each of them. While “x” and “y” are rather obvious for touch events, I don’t understand their meaning in this case (multiple fingers).

Is this event valid for pinch / expand gesture detection?