Is ist possible to get/set the radius of an existing path.circle?

Question

Starting with a path - or many of these ...

var c=paper.Path.Circle(centerPoint, 30);
c.strokeColor="";

I want to have that circle grow its radius linearly. I can do this:

var children = paper.project.activeLayer.children;
paper.view.onFrame = function(event) {
    for (var i = 0; i < children.length; i++) {
        var item = children[i];
        item.scale(1.01);
    }

But that increases the radius exponentially !

Can I get the radius of a circle and change it ? Or do I have to create a new one, deleting the old one ?
How does scale() do this ?

I also would like to delete circle larger that a given size.

Thanks, Sebastian

Answer 1

You can get the radius of a circle though it's indirect.

var radius = circle.bounds.topCenter.y - circle.bounds.center.y;

or

var radius = circle.bounds.width / 2

give you the radius of a circle. But a circle is stored as 4 segments with handles in and out, not as a circle-type object, so the radius is not stored anywhere.

In order to make it seem to grow you will have to delete the old one and draw a new one of the larger size.

It's also possible to scale it, but you want to scale it without compounding the scaling. So if you want it to grow 1.01 then 1.02 instead of 1.0201, etc. you will need to adjust the scaling factor each time.

It's not perfectly clear how you want to grow the circle, but here's some code that makes some assumptions about what you want to do:

function Scale() {
    this.original = 1.0;
    this.current = 1.0;
}

// target refers to original size in fractional terms, e.g., to
// grow by 1% specify 1.01 or to shrink by 1% specify 0.99. It returns
// the scale factor to apply to the current scale to achieve the
// target. So to increase the scale by 10% of the original size each
// time:
//
//     var s = new Scale();
//
//     for (i = 1.1; i <= 2.05; i += 0.1) {
//         var scaleFactor = s.scale(i);
//     }
//
// note the i <= 2.05 to allow for real number math issues.
//
Scale.prototype.scale = function(target) {
    // get the scaling factor from the original size
    var oFactor = target / this.original;
    // now get the factor to scale the current size by
    var cFactor = oFactor / this.current;
    this.current = oFactor;
    return cFactor;
}