Custom optimized packbits encoder

package.json

@@ -54,7 +54,6 @@
 	"copyright": "Copyright (c) 2019-2023 JrMasterModelBuilder",
 	"license": "MPL-2.0",
 	"dependencies": {
-		"@fiahfy/packbits": "0.0.6",
 		"upng-js": "^2.1.0"
 	},
 	"devDependencies": {

src/icon/icns.ts

@@ -1,8 +1,6 @@
-import {encode as packbitsEncode} from '@fiahfy/packbits';
-
 import {IImageData} from '../types';
 import {Icon} from '../icon';
-import {concatUint8Arrays} from '../util';
+import {concatUint8Arrays, packBitsIcns} from '../util';
 
 const typeArgb = ['ic04', 'ic05'];
 
@@ -343,12 +341,6 @@ export class IconIcns extends Icon {
 	 * @returns Compressed data.
 	 */
 	protected _encodePackBitsIcns(data: Readonly<Uint8Array>) {
-		const b = packbitsEncode(
-			Buffer.from(data.buffer, data.byteOffset, data.byteLength),
-			{
-				format: 'icns'
-			}
-		);
-		return new Uint8Array(b.buffer, b.byteOffset, b.byteLength);
+		return packBitsIcns(data);
 	}
 }

src/util.ts

@@ -67,3 +67,47 @@ export function pngIhdr(data: Readonly<Uint8Array>): IPngIhdr {
 
 	throw new Error('Missing PNG IHDR tag');
 }
+
+/**
+ * Encode data using PackBits ICNS compression.
+ *
+ * @param data Data to be compressed.
+ * @returns Compressed data.
+ */
+export function packBitsIcns(data: Readonly<Uint8Array>) {
+	const chunks = [];
+	const l = data.length;
+	for (let i = 0; i < l; ) {
+		const b = data[i];
+		if (i + 2 >= l) {
+			// Not enough left for anything but literal data.
+			chunks.push(new Uint8Array([l - i - 1]), data.subarray(i, l));
+			break;
+		}
+		if (b === data[i + 1] && b === data[i + 2]) {
+			// 3+ bytes repeat RLE.
+			i += 2;
+			let c = 3;
+			for (; ++i < l && b === data[i] && c < 130; c++);
+			chunks.push(new Uint8Array([c + 125, b]));
+		} else {
+			// Literal until next 3 bytes repeat.
+			let e = i + 2;
+			let c = 3;
+			for (let r = 1, p = data[e]; ++e < l && c < 128; c++) {
+				const b = data[e];
+				if (p !== b) {
+					p = b;
+					r = 1;
+				} else if (++r > 2) {
+					e -= 2;
+					c -= 2;
+					break;
+				}
+			}
+			chunks.push(new Uint8Array([c - 1]), data.subarray(i, e));
+			i = e;
+		}
+	}
+	return concatUint8Arrays(chunks);
+}