Question

I need to offset one point on line by pixels.

public static function interpolate(pt1:Point, pt2:Point, f:Number):Point
{
     var x:Number = f * pt1.x + (1 - f) * pt2.x;
     var y:Number = f * pt1.y + (1 - f) * pt2.y;

     return new Point(x, y);
}

This function can interpolate point by percent if “f” is 0.5 the point will be in the center of line pt1 pt2. Is there a way to make this with pixels?

Answer 1

it sounds like you want to write a method interpolate(pt1, pt2, distanceFromPt1). Your existing interpolate method does something similar, so you can use the latter to implement the former.

Right now, if you call interpolate(A,B,f), you get a point D where (distanceBetween(A,D) / distanceBetween(A,B)) == 1-f. In the version of interpolate you want to write, you don’t know what f should be, but you can solve for it, because you know distanceBetween(A,D).

function iterpolateByDistance(A, B, distanceFromA){
    //(dist(A,D) / dist(A,B)) == 1-f
    //f + (dist(A,D) / dist(A,B)) == 1
    //f == 1 - (dist(A,D) / dist(A,B))
    f = 1 - (distanceFromPt1 / distanceBetween(A, B));
    return interpolate(A, B, f);
}