径向渐变色对同心圆的影响

Question

如何使用html5 canvas

在5个同心圆上应用渐变颜色

    gradient = context.createRadialGradient(startx, starty,radAvg, xEnd, yEnd,radAvg);
    gradient.addColorStop(0, startColor);
    gradient.addColorStop(1.0, endColor);

当前结果：

JavaScript代码：

var colors = ["#B8D430", "#3AB745", "#029990", "#3501CB",
               "#2E2C75", "#673A7E", "#CC0071", "#F80120",
               "#F35B20", "#FB9A00", "#FFCC00", "#FEF200"];
var restaraunts = ["Wendy's", "McDonalds", "Chick-fil-a", "Five Guys",
                   "Gold Star", "La Mexicana", "Chipotle", "Tazza Mia",
                   "Panera", "Just Crepes", "Arby's", "Indian"];

var startAngle = 0;
var arc = Math.PI / 6;
var spinTimeout = null;

var spinArcStart = 10;
var spinTime = 0;
var spinTimeTotal = 0;

var ctx;

function draw() {
  drawRouletteWheel();
}

function drawRouletteWheel() {
  var canvas = document.getElementById("wheelcanvas");
  if (canvas.getContext) {
    var outsideRadius = 200;
    var textRadius = 160;
    var insideRadius = 125;

    ctx = canvas.getContext("2d");
    ctx.clearRect(0,0,500,500);


    ctx.strokeStyle = "black";
    ctx.lineWidth = 2;

    ctx.font = 'bold 12px sans-serif';

    for(var i = 0; i < 12; i++) {
      var angle = startAngle + i * arc;
      ctx.fillStyle = colors[i];

      ctx.beginPath();
      ctx.arc(250, 250, outsideRadius, angle, angle + arc, false);
      ctx.arc(250, 250, insideRadius, angle + arc, angle, true);
      ctx.stroke();
      ctx.fill();

      ctx.save();
      ctx.shadowOffsetX = -1;
      ctx.shadowOffsetY = -1;
      ctx.shadowBlur    = 0;
      ctx.shadowColor   = "rgb(220,220,220)";
    //  ctx.fillStyle = "black";
      ctx.translate(250 + Math.cos(angle + arc / 2) * textRadius, 250 + Math.sin(angle + arc / 2) * textRadius);
      ctx.rotate(angle + arc / 2 + Math.PI / 2);
      var text = restaraunts[i];
      ctx.fillText(text, -ctx.measureText(text).width / 2, 0);
      ctx.restore();
    } 

    //Arrow
    ctx.fillStyle = "black";
    ctx.beginPath();
    ctx.moveTo(250 - 4, 250 - (outsideRadius + 5));
    ctx.lineTo(250 + 4, 250 - (outsideRadius + 5));
    ctx.lineTo(250 + 4, 250 - (outsideRadius - 5));
    ctx.lineTo(250 + 9, 250 - (outsideRadius - 5));
    ctx.lineTo(250 + 0, 250 - (outsideRadius - 13));
    ctx.lineTo(250 - 9, 250 - (outsideRadius - 5));
    ctx.lineTo(250 - 4, 250 - (outsideRadius - 5));
    ctx.lineTo(250 - 4, 250 - (outsideRadius + 5));
    ctx.fill();
  }
}

function spin() {
  spinAngleStart = Math.random() * 10 + 10;
  spinTime = 0;
  spinTimeTotal = Math.random() * 3 + 4 * 1000;
  rotateWheel();
}

function rotateWheel() {
  spinTime += 30;
  if(spinTime >= spinTimeTotal) {
    stopRotateWheel();
    return;
  }
  var spinAngle = spinAngleStart - easeOut(spinTime, 0, spinAngleStart, spinTimeTotal);
  startAngle += (spinAngle * Math.PI / 180);
  drawRouletteWheel();
  spinTimeout = setTimeout('rotateWheel()', 30);
}

function stopRotateWheel() {
  clearTimeout(spinTimeout);
  var degrees = startAngle * 180 / Math.PI + 90;
  var arcd = arc * 180 / Math.PI;
  var index = Math.floor((360 - degrees % 360) / arcd);
  ctx.save();
  ctx.font = 'bold 30px sans-serif';
  var text = restaraunts[index]
  ctx.fillText(text, 250 - ctx.measureText(text).width / 2, 250 + 10);
  ctx.restore();
}

function easeOut(t, b, c, d) {
  var ts = (t/=d)*t;
  var tc = ts*t;
  return b+c*(tc + -3*ts + 3*t);
}

draw();

Answer 1

这是我的解决方案

 var Mid_diff=(startAngle+endAngle)/2;
 var dest_x=arc.center.x+(arc.maxRadius*Math.cos(Mid_diff));
 var dest_y=arc.center.y+(arc.maxRadius*Math.sin(Mid_diff));

 var gradient = context.createRadialGradient( arc.center.x,arc.center.y,0,dest_x,dest_y,arc.maxRadius);
 gradient.addColoStop(0,rgba(0,12,107,0);
 gradient.addColoStop(1,rgba(0,12,107,1);
 context.strokeStyle = gradient;

工作