Added default map inset and grid size heuristic

src/helpers/map.js

@@ -0,0 +1,53 @@
+export function getMapDefaultInset(width, height, gridX, gridY) {
+  // Max the width
+  const gridScale = width / gridX;
+  const y = gridY * gridScale;
+  const yNorm = y / height;
+  return { topLeft: { x: 0, y: 0 }, bottomRight: { x: 1, y: yNorm } };
+}
+
+// Get all factors of a number
+function factors(n) {
+  const numbers = Array.from(Array(n + 1), (_, i) => i);
+  return numbers.filter((i) => n % i === 0);
+}
+
+// Greatest common divisor
+// Euclidean algorithm https://en.wikipedia.org/wiki/Euclidean_algorithm
+function gcd(a, b) {
+  while (b !== 0) {
+    const t = b;
+    b = a % b;
+    a = t;
+  }
+  return a;
+}
+
+// Find all dividers that fit into two numbers
+function dividers(a, b) {
+  const d = gcd(a, b);
+  return factors(d);
+}
+
+const commonGridScales = [70, 111, 140, 300];
+
+export function gridSizeHeuristic(width, height) {
+  const div = dividers(width, height);
+  if (div.length > 0) {
+    // default to middle divider
+    let scale = div[Math.floor(div.length / 2)];
+    for (let common of commonGridScales) {
+      // Check common but make sure the grid size is above 10
+      if (div.includes(common) && width / common > 10 && height / common > 10) {
+        scale = common;
+      }
+    }
+    const x = Math.floor(width / scale);
+    const y = Math.floor(height / scale);
+    // Check grid size is below 100
+    if (x < 100 && y < 100) {
+      return { x, y };
+    }
+  }
+  return { x: 22, y: 22 };
+}