Question 246437 in Javascript Question posted in
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Javascript – How to determine if a circle is inside a circle using Paper.js?

How can one determine if a circle is inside another circle? I thought I had it figured out using isInside method.

Note: This code will run on http://sketch.paperjs.org

Expect Circle2 to be inside Circle1

var circle1 = new Path.Circle(new Point(100, 100), 100);
var circle2 = new Path.Circle(new Point(100, 100), 50);

circle1.strokeWidth = 2;
circle1.strokeColor = "black";
circle1.fillColor = "blue";
circle2.strokeWidth = 2;
circle2.strokeColor = "black";
circle2.fillColor = "green";

console.log(circle1.isInside(circle2));
console.log(circle2.isInside(circle1));

Outputs:

false false

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    From the docs isInside requires a rectangle object to be passed in as a parameter, not a path.

    Working Code

    var circle1 = new Path.Circle(new Point(100, 100), 100);
var circle2 = new Path.Circle(new Point(100, 100), 50);

circle1.strokeWidth = 2;
circle1.strokeColor = "black";
circle1.fillColor = "blue";
circle2.strokeWidth = 2;
circle2.strokeColor = "black";
circle2.fillColor = "green";

console.log(circle1.isInside(circle2.bounds));
console.log(circle2.isInside(circle1.bounds));

    Outputs:

    false true


  2. 0

    To know if circle_small with radius Rs is enterely inside circle_big with radius Rb just check that the distance between their centers (Cb, Cs) is less than Rb-Rs.

    If you allow both circles "touch" in one point then the condition is less or equal to Rb-Rs.

    General case:

    var discen = Math.sqrt( (Cb_x - Cs_x)*(Cb_x - Cs_x) + (Cb_y - Cs_y)*(Cb_y - Cs_y) );
var radiff = Rb - Rs;
if (discen < radiff)
    //circle_small fully inside circle_big, no touching point
else if ( Math.abs(discen-radiff) < 0.0001 ) //better that discen==radiff
    //circle_small fully inside circle_big, one tangent common (touching point)
else if (discen < Rb+Rs)
    //Both circles intersect, partially one inside the other
else
    //Not intersecting circles
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