Get arc for circle.

gistfile1.ts

/**
 * Get an arc (circle segment) between two points.
 * @param x0 The x-coordinate of the arc's starting point.
 * @param y0 The y-coordinate of the arc's starting point.
 * @param a0 The angle in radians of the arc's starting point.
 * @param x1 The x-coordinate of the arc's ending point.
 * @param y1 The y-coordinate of the arc's ending point.
 * @param a1 The angle in radians of the arc's ending point.
 * @param r  The radius of the circle.
 * @param flip Whether to flip the segment.
 */
function getArcPath(
  x0: number,
  y0: number,
  a0: number,
  x1: number,
  y1: number,
  a1: number,
  r: number,
  flip: boolean
) {
  if (a1 < a0) a1 += Math.PI * 2
  let largeArc = Math.abs(a1 - a0) > Math.PI ? 1 : 0
  if (flip) largeArc = Math.abs(largeArc - 1)

  return `M ${x0},${y0} A ${r},${r} 0 ${largeArc} ${
    flip ? 0 : 1
  } ${x1} ${y1}`
}

// Based on http://madebyevan.com/fsm/