Can't get transformed points out of a kinetic JS line

Question

I have been able to successfully draw a line using Kinetic JS, as follows:

var track129 = new Kinetic.Spline({
points: [
{x: 3, y: 400}, 
{x: 196, y: 400}, 
{x: 213, y: 395}, 
{x: 290, y: 345},
{x: 319, y: 324},
{x: 389, y: 253},
{x: 457, y: 184},
{x: 471, y: 173},
{x: 481, y: 173},
{x: 682, y: 173}, // this is where the blue track branches to the red track (129, 009).
{x: 708, y: 171},
{x: 740, y: 186},
{x: 773, y: 218},
{x: 799, y: 240},
{x: 822, y: 251},
{x: 845, y: 254},
{x: 866, y: 251},
{x: 894, y: 238},
{x: 934, y: 204}        
],
stroke: 'blue',
strokeWidth: 2,
lineCap: 'round',
tension: .2
});

layer.add(track129);

I then rotate the line using the following command:

track129.setRotationDeg(45);

The visual display updates. I then attempt to get the transformed points out of the rotated line like so:

var mySpleenPoints = track129.getPoints(); 

I end up getting the same array of points back as I entered. I've tried to get the offset and translation in an effort to see if I can derive the absolute coordinates of the rotated points but I've had no luck. Can anyone help me extract the actual translated values?

Answer 1

sorry, the rotation doesn't actually translate the point values, so you're getting correct output. If you want the translated values, you will have to write a function which calculates the coordinates. The good thing is that you have all the values you need to do that. Rotation degree, coordinates, and rotation around point.

I think this is the equation (for rotation around the origin)

 x' = x * cos(Theta) - y * sin(Theta);
 y' = x * sin(Theta) + y * cos(Theta); 

HTML5 Canvas: Calculating a x,y point when rotated

https://math.stackexchange.com/questions/123098/finding-the-position-of-a-point-after-rotation-why-is-my-result-incorrect

Answer 2

That is a really irritating behavior. Anyway, thanks for the post. I am providing code for anyone who encounters this problem in the future.

function degToRad(angle) {
return (angle / 180) * Math.PI;
}

function rotateVector ( v, center, angle ) {
var theta = degToRad(angle);        
var s = Math.sin(theta);

var c = Math.cos(theta);

var nx = c * (v.x -center.x) + center.x - s * (v.y - center.y);
var ny = s * (v.x - center.x) + c * (v.y - center.y) + center.y;

v.x = nx;
v.y = ny;

return v;
};