ThreePointCubic constructor Null safety
Creates two cubic curves that share a common control point.
Rather than creating a new instance, consider using one of the common three-point cubic curves in Curves.
The arguments correspond to the control points for the two curves, including the midpoint, but do not include the two implied end points at (0,0) and (1,1), which are fixed.
const ThreePointCubic(this.a1, this.b1, this.midpoint, this.a2, this.b2);