Add arrow key polygon movement

russellashby · claude · russellashby · commit ea7cb00a3af1 · 2026-03-10T10:05:23.000Z
Arrow keys translate all vertices by 1 grid unit, clamped to grid bounds.
New translateVertices pure function in vector.js with 4 test suites (61
total tests passing).

Co-Authored-By: Claude Opus 4.6 &lt;noreply@anthropic.com&gt;
diff --git a/index.html b/index.html
@@ -721,6 +721,14 @@ <h2>Lua Output</h2>
   if (e.key === 'c' && !e.ctrlKey && !e.metaKey) {
     document.getElementById('closeBtn').click();
   }
+  // Arrow keys to move closed polygon
+  if (['ArrowUp', 'ArrowDown', 'ArrowLeft', 'ArrowRight'].includes(e.key) && vertices.length > 0) {
+    e.preventDefault();
+    const dx = e.key === 'ArrowLeft' ? -1 : e.key === 'ArrowRight' ? 1 : 0;
+    const dy = e.key === 'ArrowUp' ? -1 : e.key === 'ArrowDown' ? 1 : 0;
+    vertices = translateVertices(vertices, dx, dy, gridSize);
+    refresh();
+  }
 });
 
 // Init
diff --git a/tests.js b/tests.js
@@ -1,4 +1,4 @@
-const { gridToCanvas, canvasToGrid, rotatePoint, getEffectiveVertices, parseLuaTable, generateLuaOutput } = require('./vector.js');
+const { gridToCanvas, canvasToGrid, rotatePoint, getEffectiveVertices, parseLuaTable, generateLuaOutput, translateVertices } = require('./vector.js');
 
 let passed = 0;
 let failed = 0;
@@ -227,6 +227,36 @@ suite('generateLuaOutput -> parseLuaTable roundtrip', () => {
   }
 });
 
+// ── translateVertices ──
+
+suite('translateVertices — basic move', () => {
+  const verts = [[0, 0], [2, 3]];
+  const moved = translateVertices(verts, 1, -1, 32);
+  assert(moved[0][0] === 1 && moved[0][1] === -1, 'first vertex moved');
+  assert(moved[1][0] === 3 && moved[1][1] === 2, 'second vertex moved');
+});
+
+suite('translateVertices — clamping to grid bounds', () => {
+  const verts = [[15, 15]];
+  const moved = translateVertices(verts, 5, 5, 32);
+  assert(moved[0][0] === 16 && moved[0][1] === 16, 'clamped to grid half');
+
+  const moved2 = translateVertices([[-15, -15]], -5, -5, 32);
+  assert(moved2[0][0] === -16 && moved2[0][1] === -16, 'clamped to negative bound');
+});
+
+suite('translateVertices — zero movement', () => {
+  const verts = [[3, 4]];
+  const moved = translateVertices(verts, 0, 0, 32);
+  assert(moved[0][0] === 3 && moved[0][1] === 4, 'unchanged');
+});
+
+suite('translateVertices — does not mutate original', () => {
+  const verts = [[1, 2]];
+  translateVertices(verts, 5, 5, 32);
+  assert(verts[0][0] === 1 && verts[0][1] === 2, 'original unchanged');
+});
+
 // ── Summary ──
 
 console.log(`\n${'='.repeat(40)}`);
diff --git a/vector.js b/vector.js
@@ -102,6 +102,14 @@ function generateLuaOutput(vertices, scaleFactor) {
   return lua;
 }
 
+function translateVertices(vertices, dx, dy, gridSize) {
+  const half = gridSize / 2;
+  return vertices.map(([x, y]) => [
+    Math.max(-half, Math.min(half, x + dx)),
+    Math.max(-half, Math.min(half, y + dy))
+  ]);
+}
+
 if (typeof module !== 'undefined' && module.exports) {
-  module.exports = { gridToCanvas, canvasToGrid, rotatePoint, getEffectiveVertices, parseLuaTable, generateLuaOutput };
+  module.exports = { gridToCanvas, canvasToGrid, rotatePoint, getEffectiveVertices, parseLuaTable, generateLuaOutput, translateVertices };
 }
