abstract jpeg encoding away from "WSServer"

Additionally make thumbnail encoding threadpooled as well, just so it (probably) doesn't block as much.

cvmts/src/JPEGEncoder.ts

@@ -0,0 +1,59 @@
+import path from 'node:path';
+import Piscina from 'piscina';
+
+import { Size, Rect } from '@cvmts/shared';
+
+const kMaxJpegThreads = 4;
+const kIdleTimeout = 25000;
+
+// Thread pool for doing JPEG encoding for rects.
+const TheJpegEncoderPool = new Piscina({
+	filename: path.join(import.meta.dirname + '/JPEGEncoderWorker.js'),
+	idleTimeout: kIdleTimeout,
+	maxThreads: kMaxJpegThreads
+});
+
+const TheThumbnailEncoderPool = new Piscina({
+	filename: path.join(import.meta.dirname + '/ThumbnailJPEGEncoderWorker.js'),
+	idleTimeout: kIdleTimeout,
+	maxThreads: kMaxJpegThreads
+});
+
+// A good balance. TODO: Configurable?
+let gJpegQuality = 35;
+
+export class JPEGEncoder {
+
+	static SetQuality(quality: number) {
+		gJpegQuality = quality;
+	}
+
+	static async EncodeJpeg(canvas: Buffer, displaySize: Size, rect: Rect): Promise<Buffer> {
+		let offset = (rect.y * displaySize.width + rect.x) * 4;
+
+		let res = await TheJpegEncoderPool.run({
+			buffer: canvas.subarray(offset),
+			width: rect.width,
+			height: rect.height,
+			stride: displaySize.width,
+			quality: gJpegQuality
+		});
+
+		// TODO: There's probably (definitely) a better way to fix this
+		if (res == undefined) return Buffer.from([]);
+
+		// have to manually turn it back into a buffer because
+		// Piscina for some reason turns it into a Uint8Array
+		return Buffer.from(res);
+	}
+
+	static async EncodeThumbnail(buffer: Buffer, size: Size) : Promise<Buffer>  {
+		let res = await TheThumbnailEncoderPool.run({
+			buffer: buffer,
+			size: size,
+			quality: gJpegQuality
+		});
+
+		return Buffer.from(res)
+	}
+}