deferred drawing

canvas.ts

@@ -89,6 +89,7 @@ export class Doodler {
     // }
     for (const [i, l] of (this.layers || []).entries()) {
       l(this.ctx, i);
+      this.drawDeferred();
     }
     this.drawUI();
   }
@@ -227,6 +228,18 @@ export class Doodler {
     );
   }
 
+  private deferredDrawings: (() => void)[] = [];
+
+  deferDrawing(cb: () => void) {
+    this.deferredDrawings.push(cb);
+  }
+
+  drawDeferred() {
+    while (this.deferredDrawings.length) {
+      this.deferredDrawings.pop()?.();
+    }
+  }
+
   setStyle(style?: IStyle) {
     const ctx = this.ctx;
     ctx.fillStyle = style?.color || style?.fillColor || "black";