gradientAtPointAlongPathFrom(curve, location, distance): number
Returns the gradient of the curve at the point which is 'distance' from the given location.
if this point is greater than location 1, the gradient at location 1 is returned.
if this point is less than location 0, the gradient at location 0 is returned.
Returns the gradient of the curve at the point which is 'distance' from the given location. if this point is greater than location 1, the gradient at location 1 is returned. if this point is less than location 0, the gradient at location 0 is returned.