Charts & Diagrams

// Usage: 
drawLineWithArrows(50,50,150,50,5,8,true,true);

// x0,y0: the line's starting point
// x1,y1: the line's ending point
// width: the distance the arrowhead perpendicularly extends away from the line
// height: the distance the arrowhead extends backward from the endpoint
// arrowStart: true/false directing to draw arrowhead at the line's starting point
// arrowEnd: true/false directing to draw arrowhead at the line's ending point

function drawLineWithArrows(x0,y0,x1,y1,aWidth,aLength,arrowStart,arrowEnd){
    var dx=x1-x0;
    var dy=y1-y0;
    var angle=Math.atan2(dy,dx);
    var length=Math.sqrt(dx*dx+dy*dy);
    //
    ctx.translate(x0,y0);
    ctx.rotate(angle);
    ctx.beginPath();
    ctx.moveTo(0,0);
    ctx.lineTo(length,0);
    if(arrowStart){
        ctx.moveTo(aLength,-aWidth);
        ctx.lineTo(0,0);
        ctx.lineTo(aLength,aWidth);
    }
    if(arrowEnd){
        ctx.moveTo(length-aLength,-aWidth);
        ctx.lineTo(length,0);
        ctx.lineTo(length-aLength,aWidth);
    }
    //
    ctx.stroke();
    ctx.setTransform(1,0,0,1,0,0);
}

// Usage:
var p0={x:50,y:100};
var p1={x:100,y:0};
var p2={x:200,y:200};
var p3={x:300,y:100};

cubicCurveArrowHeads(p0, p1, p2, p3, 15, true, true);

quadraticCurveArrowHeads(p0, p1, p2, 15, true, true);

// or use defaults true for both ends with arrow heads
cubicCurveArrowHeads(p0, p1, p2, p3, 15);

quadraticCurveArrowHeads(p0, p1, p2, 15);



// draws both cubic and quadratic bezier
function bezWithArrowheads(p0, p1, p2, p3, arrowLength, hasStartArrow, hasEndArrow) {
    var x, y, norm, ex, ey;
    function pointsToNormalisedVec(p,pp){
        var len;
        norm.y = pp.x - p.x;
        norm.x = -(pp.y - p.y);
        len = Math.sqrt(norm.x * norm.x + norm.y * norm.y);
        norm.x /= len;
        norm.y /= len;
        return norm;
    }
        
    var arrowWidth = arrowLength / 2;
    norm = {};
    // defaults to true for both arrows if arguments not included
    hasStartArrow = hasStartArrow === undefined || hasStartArrow === null ? true : hasStartArrow;
    hasEndArrow = hasEndArrow === undefined || hasEndArrow === null ? true : hasEndArrow;
    ctx.beginPath();
    ctx.moveTo(p0.x, p0.y);
    if (p3 === undefined) {
        ctx.quadraticCurveTo(p1.x, p1.y, p2.x, p2.y);
        ex = p2.x;  // get end point
        ey = p2.y;
        norm = pointsToNormalisedVec(p1,p2);
    } else {
        ctx.bezierCurveTo(p1.x, p1.y, p2.x, p2.y, p3.x, p3.y)
        ex = p3.x; // get end point
        ey = p3.y;
        norm = pointsToNormalisedVec(p2,p3);
    }
    if (hasEndArrow) {
        x = arrowWidth * norm.x + arrowLength * -norm.y;
        y = arrowWidth * norm.y + arrowLength * norm.x;
        ctx.moveTo(ex + x, ey + y);
        ctx.lineTo(ex, ey);
        x = arrowWidth * -norm.x + arrowLength * -norm.y;
        y = arrowWidth * -norm.y + arrowLength * norm.x;
        ctx.lineTo(ex + x, ey + y);
    }
    if (hasStartArrow) {
        norm = pointsToNormalisedVec(p0,p1);
        x = arrowWidth * norm.x - arrowLength * -norm.y;
        y = arrowWidth * norm.y - arrowLength * norm.x;
        ctx.moveTo(p0.x + x, p0.y + y);
        ctx.lineTo(p0.x, p0.y);
        x = arrowWidth * -norm.x - arrowLength * -norm.y;
        y = arrowWidth * -norm.y - arrowLength * norm.x;
        ctx.lineTo(p0.x + x, p0.y + y);
    }

    ctx.stroke();
}

function cubicCurveArrowHeads(p0, p1, p2, p3, arrowLength, hasStartArrow, hasEndArrow) {
    bezWithArrowheads(p0, p1, p2, p3, arrowLength, hasStartArrow, hasEndArrow);
}
function quadraticCurveArrowHeads(p0, p1, p2, arrowLength, hasStartArrow, hasEndArrow) {
    bezWithArrowheads(p0, p1, p2, undefined, arrowLength, hasStartArrow, hasEndArrow);
}
    

// Usage
var wedge={
    cx:150, cy:150,
    radius:100,
    startAngle:0,
    endAngle:Math.PI*.65
}

drawWedge(wedge,'skyblue','gray',4);

function drawWedge(w,fill,stroke,strokewidth){
    ctx.beginPath();
    ctx.moveTo(w.cx, w.cy);
    ctx.arc(w.cx, w.cy, w.radius, w.startAngle, w.endAngle);
    ctx.closePath();
    ctx.fillStyle=fill;
    ctx.fill();
    ctx.strokeStyle=stroke;
    ctx.lineWidth=strokewidth;
    ctx.stroke();
}

// Usage:
var arc={
    cx:150, cy:150,
    innerRadius:75, outerRadius:100,
    startAngle:-Math.PI/4, endAngle:Math.PI
}

drawArc(arc,'skyblue','gray',4);

function drawArc(a,fill,stroke,strokewidth){
    ctx.beginPath();
    ctx.arc(a.cx,a.cy,a.innerRadius,a.startAngle,a.endAngle);
    ctx.arc(a.cx,a.cy,a.outerRadius,a.endAngle,a.startAngle,true);
    ctx.closePath();
    ctx.fillStyle=fill;
    ctx.strokeStyle=stroke;
    ctx.lineWidth=strokewidth
    ctx.fill();
    ctx.stroke();
}

<!doctype html>
<html>
<head>
<style>
    body{ background-color:white; }
    #canvas{border:1px solid red; }
</style>
<script>
window.onload=(function(){

    var canvas = document.getElementById("canvas");
    var ctx = canvas.getContext("2d");
    ctx.lineWidth = 2;
    ctx.font = '14px verdana';

    var PI2 = Math.PI * 2;
    var myColor = ["Green", "Red", "Blue"];
    var myData = [30, 60, 10];
    var cx = 150;
    var cy = 150;
    var radius = 100;

    pieChart(myData, myColor);

    function pieChart(data, colors) {
      var total = 0;
      for (var i = 0; i < data.length; i++) {
        total += data[i];
      }

      var sweeps = []
      for (var i = 0; i < data.length; i++) {
        sweeps.push(data[i] / total * PI2);
      }

      var accumAngle = 0;
      for (var i = 0; i < sweeps.length; i++) {
        drawWedge(accumAngle, accumAngle + sweeps[i], colors[i], data[i]);
        accumAngle += sweeps[i];
      }
    }

    function drawWedge(startAngle, endAngle, fill, label) {
      // draw the wedge
      ctx.beginPath();
      ctx.moveTo(cx, cy);
      ctx.arc(cx, cy, radius, startAngle, endAngle, false);
      ctx.closePath();
      ctx.fillStyle = fill;
      ctx.strokeStyle = 'black';
      ctx.fill();
      ctx.stroke();

      // draw the label
      var midAngle = startAngle + (endAngle - startAngle) / 2;
      var labelRadius = radius * .65;
      var x = cx + (labelRadius) * Math.cos(midAngle);
      var y = cy + (labelRadius) * Math.sin(midAngle);
      ctx.fillStyle = 'white';
      ctx.fillText(label, x, y);
    }

}); // end $(function(){});
</script>
</head>
<body>
    <canvas id="canvas" width=512 height=512></canvas>
</body>
</html>