キャンバスポリゴン描画方式

function drawPolygonPath(sideNum, radius, originX, originY, ctx){
  ctx.beginPath();
  const unitAngle = Math.PI * 2 / sideNum; // calculate the unit angle
  let angle = 0; //initial angle
  let xLength, yLength;
  // ctx.moveTo(originX, originY);
  for(let i = 0; i < sideNum; i++){ // iterate through the calculated points and lineTo() draw the path
    xLength = radius * Math.cos(angle);
    yLength = radius * Math.sin(angle);
    ctx.lineTo(originX + xLength, originY - yLength);//draw the path
    angle += unitAngle;
  }
  ctx.closePath();//close the path, also loop lineTo() more than once in the for loop to the starting point
}