curveTangent()

Calculates coordinates along a line that's tangent to a spline curve.

Tangent lines skim the surface of a curve. A tangent line's slope equals the curve's slope at the point where it intersects.

curveTangent() calculates coordinates along a tangent line using the spline curve's anchor and control points. It expects points in the same order as the curve() function. curveTangent() works one axis at a time. Passing the anchor and control points' x-coordinates will calculate the x-coordinate of a point on the tangent line. Passing the anchor and control points' y-coordinates will calculate the y-coordinate of a point on the tangent line.

The first parameter, a, is the coordinate of the first control point.

The second and third parameters, b and c, are the coordinates of the anchor points.

The fourth parameter, d, is the coordinate of the last control point.

The fifth parameter, t, is the amount to interpolate along the curve. 0 is the first anchor point, 1 is the second anchor point, and 0.5 is halfway between them.