Javascript forma de triángulo de lona html5 con esquinas redondeadas

Crea una ruta a partir de un conjunto de puntos [{x:?,y:?},{x:?,y:?},...,{x:?,y:?}] con esquinas redondeadas de radio.

Ejemplo de uso

HTML

<canvas id="myCanvas" width="210" height="210"></canvas>

JAVASCRIPT

var canvasElement = document.querySelector("#myCanvas");  
var ctx = canvasElement.getContext("2d");  
  
var triangle = [  
    { x: 100, y: 0 },  
    { x: 0, y: 200 },  
    { x: 200, y: 200 }  
];  
var cornerRadius = 10;  
ctx.lineWidth = 4;  
ctx.fillStyle = "blue";  
ctx.strokeStyle = "black";  
ctx.beginPath(); // start a new path  
roundedPoly(triangle, cornerRadius);  
ctx.fill();  
ctx.stroke();

Representar forma de triángulo de lienzo con función redondeada

var roundedPoly = function(points,radius){  
    var i, x, y, len, p1, p2, p3, v1, v2, sinA, sinA90, radDirection, drawDirection, angle, halfAngle, cRadius, lenOut;  
    var asVec = function(p, pp, v) { // convert points to a line with len and normalised  
        v.x = pp.x- p.x; // x,y as vec  
        v.y = pp.y- p.y;  
        v.len = Math.sqrt(v.x * v.x + v.y * v.y); // length of vec  
        v.nx = v.x / v.len; // normalised  
        v.ny = v.y / v.len;  
        v.ang = Math.atan2(v.ny, v.nx); // direction of vec  
    }  
    v1 = {};  
    v2 = {};  
    len = points.length;                         // number points  
    p1 = points[len- 1];                        // start at end of path  
    for(i = 0; i < len; i++) {                  // do each corner  
        p2 = points[(i) % len];                  // the corner point that is being rounded  
        p3 = points[(i + 1) % len];  
        // get the corner as vectors out away from corner  
        asVec(p2, p1, v1);                       // vec back from corner point  
        asVec(p2, p3, v2);                       // vec forward from corner point  
        // get corners cross product(asin of angle)  
        sinA = v1.nx * v2.ny- v1.ny * v2.nx;    // cross product  
        // get cross product of first line and perpendicular second line  
        sinA90 = v1.nx * v2.nx- v1.ny * -v2.ny; // cross product to normal of line 2  
        angle = Math.asin(sinA);                 // get the angle  
        radDirection = 1;                        // may need to reverse the radius  
        drawDirection = false;                   // may need to draw the arc anticlockwise  
        // find the correct quadrant for circle center  
        if(sinA90 < 0) {  
            if(angle < 0) {  
                angle = Math.PI + angle; // add 180 to move us to the 3 quadrant  
            } else {  
                angle = Math.PI- angle; // move back into the 2nd quadrant  
                radDirection = -1;  
                drawDirection = true;  
            }  
        } else {  
            if(angle > 0) {  
                radDirection = -1;  
                drawDirection = true;  
            }  
        }  
        halfAngle = angle / 2;  
        // get distance from corner to point where round corner touches line  
        lenOut = Math.abs(Math.cos(halfAngle) * radius / Math.sin(halfAngle));  
        if(lenOut > Math.min(v1.len / 2, v2.len / 2)) { // fix if longer than half line length  
            lenOut = Math.min(v1.len / 2, v2.len / 2);  
            // ajust the radius of corner rounding to fit  
            cRadius = Math.abs(lenOut * Math.sin(halfAngle) / Math.cos(halfAngle));  
        } else {  
            cRadius = radius;  
        }  
        x = p2.x + v2.nx * lenOut; // move out from corner along second line to point where rounded circle touches  
        y = p2.y + v2.ny * lenOut;  
        x += -v2.ny * cRadius * radDirection; // move away from line to circle center  
        y += v2.nx * cRadius * radDirection;  
        // x,y is the rounded corner circle center  
        ctx.arc(x, y, cRadius, v1.ang + Math.PI / 2 * radDirection, v2.ang- Math.PI / 2 * radDirection, drawDirection); // draw the arc clockwise  
        p1 = p2;  
        p2 = p3;  
    }  
    ctx.closePath();  
}