P1 = (x1,y1), P2 = (x2,y2) / x ranges 0–1, y can be any value (roughly -1 to 2 allowed)
Linear mode: Click inside the editor to add points / Alt+Click to delete (endpoints cannot be removed) / Drag points to edit
3 Preview
The bar uses CSS Transition, the box uses Transform + Transition. Duration/Delay/Easing are shared.