Moved minimap rendering to offscreen canvas

src/renderer/minimapWorker.ts

@@ -0,0 +1,48 @@
+/* eslint-disable no-restricted-globals */
+
+import { getNonDeletedElements } from "../element";
+import { ExcalidrawElement } from "../element/types";
+import { exportToCanvas } from "../scene/export";
+import { AppState } from "../types";
+
+const ctx: Worker = self as any;
+let canvas: OffscreenCanvas;
+
+ctx.addEventListener("message", (ev) => {
+  if (ev.data.type === "INIT") {
+    canvas = ev.data.canvas;
+  }
+
+  if (ev.data.type === "DRAW") {
+    const { elements, appState, width, height } = ev.data;
+    drawScene(canvas, elements, appState, width, height);
+  }
+});
+
+function drawScene(
+  canvas: OffscreenCanvas,
+  elements: readonly ExcalidrawElement[],
+  appState: AppState,
+  minimapWidth: number,
+  minimapHeight: number,
+) {
+  exportToCanvas(
+    getNonDeletedElements(elements),
+    appState,
+    {
+      exportBackground: true,
+      viewBackgroundColor: appState.viewBackgroundColor,
+      shouldAddWatermark: false,
+    },
+    (width, height) => {
+      const scale = Math.min(minimapWidth / width, minimapHeight / height);
+      canvas.width = width * scale;
+      canvas.height = height * scale;
+
+      return {
+        canvas,
+        scale,
+      };
+    },
+  );
+}