Implemented a fallback main thread loader and renderer to support for legacy browsers.

src/pgsRendererInMainThread.ts

@@ -0,0 +1,67 @@
+import {PgsRendererImpl} from "./pgsRendererImpl";
+import {PgsRendererOptions} from "./pgsRendererOptions";
+import {Renderer} from "./renderer";
+import {Pgs} from "./pgs";
+
+/**
+ * The implementation without web workers. This loads and renders the subtitle in the main thread.
+ * This is meant as a compatibility fallback if advanced workers are not supported.
+ */
+export class PgsRendererInMainThread extends PgsRendererImpl {
+
+    public constructor(options: PgsRendererOptions, canvas: HTMLCanvasElement) {
+        super();
+
+        this.pgs = new Pgs();
+        this.renderer = new Renderer(canvas);
+    }
+
+    /**
+     * The PGS loader.
+     * @private
+     */
+    private readonly pgs: Pgs;
+
+    /**
+     * The subtitle renderer, running in the main thread.
+     */
+    private readonly renderer: Renderer;
+
+    protected render(index: number): void {
+        const subtitleData = this.pgs.getSubtitleAtIndex(index);
+        requestAnimationFrame(() => {
+            this.renderer.draw(subtitleData);
+        });
+        this.pgs.cacheSubtitleAtIndex(index + 1);
+    }
+
+    public loadFromUrl(url: string): void {
+        this.pgs.loadFromUrl(url, {
+            onProgress: () => {
+                this.invokeTimestampsUpdate();
+            }
+        }).then(() => {
+            this.invokeTimestampsUpdate();
+        });
+    }
+
+    public loadFromBuffer(buffer: ArrayBuffer): void {
+        this.pgs.loadFromBuffer(buffer).then(() => {
+            this.invokeTimestampsUpdate();
+        });
+    }
+
+    /**
+     * Submits the update timestamps from the pgs loader and invokes events.
+     */
+    private invokeTimestampsUpdate(): void {
+        this.setUpdateTimestamps(this.pgs.updateTimestamps);
+    }
+
+    /**
+     * Disposes the renderer.
+     */
+    public dispose(): void {
+        // Nothing to do
+    }
+}