LED wall active area: confine the output to a pixel-mapping rectangle

New 'Area LED' controls in the Schermo tab: W x H @ X,Y. Everything
(canvas, videos, images, logos, ticker) lives in a #stage box whose
transform makes it the containing block for the fixed layers, so resizing
it confines the whole show at once, black outside. The canvas resizes to
the stage, so shaders render at the wall's native resolution. Persisted
in localStorage and re-pushed when the output window (re)starts; the
recorder follows the canvas position.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/control.js

@@ -1094,6 +1094,25 @@ $('#btn-display').addEventListener('click', () => {
 });
 $('#btn-fullscreen').addEventListener('click', () => djv.toggleOutputFullscreen());
 
+// ---- LED wall active area (pixel-mapping processors) ----
+// Persisted; re-sent whenever the output window (re)starts (see 'devices').
+let ledCfg = { on: false, w: 1024, h: 576, x: 0, y: 0 };
+try { ledCfg = Object.assign(ledCfg, JSON.parse(localStorage.getItem('ledarea') || '{}')); } catch (e) {}
+function ledSend() { send({ type: 'ledArea', on: ledCfg.on, w: ledCfg.w, h: ledCfg.h, x: ledCfg.x, y: ledCfg.y }); }
+function ledSave() { localStorage.setItem('ledarea', JSON.stringify(ledCfg)); ledSend(); }
+(function ledInit() {
+  $('#led-on').checked = ledCfg.on;
+  const fields = [['#led-w', 'w'], ['#led-h', 'h'], ['#led-x', 'x'], ['#led-y', 'y']];
+  fields.forEach(([sel, k]) => {
+    $(sel).value = ledCfg[k];
+    $(sel).addEventListener('change', (e) => {
+      ledCfg[k] = Math.max(0, parseInt(e.target.value || '0', 10) || 0);
+      ledSave();
+    });
+  });
+  $('#led-on').addEventListener('change', (e) => { ledCfg.on = e.target.checked; ledSave(); });
+})();
+
 // ---------------------------------------------------------------- recording
 let recOn = false, recTimer = null, recStartedAt = 0;
 function fmtTime(s) {
@@ -1371,6 +1390,9 @@ djv.onReport((m) => {
       }
       break;
     case 'devices': {
+      // The output reports its devices once at startup: good moment to push
+      // config the (possibly recreated) output window doesn't have yet.
+      if (ledCfg.on) ledSend();
       const sel = $('#device-select');
       const cur = sel.value;
       sel.innerHTML = '<option value="">— Input live (mic/line/BlackHole) —</option>';