1 files changed, 37 insertions, 0 deletions
diff --git a/src/arc.ts b/src/arc.ts
new file mode 100644
index 0000000..d8e1e7d
--- /dev/null
+++ b/src/arc.ts
@@ -0,0 +1,37 @@
+function polarToCartesian(
+  centerX: number,
+  centerY: number,
+  radius: number,
+  degreesAngle: number
+): number[] {
+  const radianAngle = (degreesAngle - 90) * Math.PI / 180
+  return [
+    centerX + radius * Math.cos(radianAngle),
+    centerY + radius * Math.sin(radianAngle)
+  ]
+}
+
+export function describe(
+  x: number,
+  y: number,
+  radius: number,
+  startAngle: number,
+  endAngle: number
+): string {
+  const [startX, startY] = polarToCartesian(x, y, radius, endAngle)
+  const [endX, endY] = polarToCartesian(x, y, radius, startAngle)
+  const largeArcFlag = endAngle - startAngle <= 180 ? "0" : "1"
+  return [
+    "M",
+    startX.toString(),
+    startY,
+    "A",
+    radius.toString(),
+    radius.toString(),
+    "0",
+    largeArcFlag,
+    "0",
+    endX.toString(),
+    endY.toString(),
+  ].join(" ")
+}