Track which decoders prefer to be run in a worker

Author: constantinius

src/compression/index.js

@@ -1,12 +1,27 @@
 const registry = new Map();
+const preferWorkerMap = new Map();
 
-export function addDecoder(cases, importFn) {
+/**
+ * Register a decoder for a specific compression method or a range of compressions
+ * @param {(number|undefined|(number|undefined)[]))} cases ids of the compression methods to register for
+ * @param {function():Promise} importFn the function to import the decoder
+ * @param {boolean} preferWorker_ Whether to prefer running the decoder in a worker
+ */
+export function addDecoder(cases, importFn, preferWorker_ = true) {
   if (!Array.isArray(cases)) {
     cases = [cases]; // eslint-disable-line no-param-reassign
   }
-  cases.forEach((c) => registry.set(c, importFn));
+  cases.forEach((c) => {
+    registry.set(c, importFn);
+    preferWorkerMap.set(c, preferWorker_);
+  });
 }
 
+/**
+ * Get a decoder for a specific file directory
+ * @param {object} fileDirectory the file directory of the image
+ * @returns {Promise<Decoder>}
+ */
 export async function getDecoder(fileDirectory) {
   const importFn = registry.get(fileDirectory.Compression);
   if (!importFn) {
@@ -16,8 +31,17 @@ export async function getDecoder(fileDirectory) {
   return new Decoder(fileDirectory);
 }
 
+/**
+ * Whether to prefer running the decoder in a worker
+ * @param {object} fileDirectory the file directory of the image
+ * @returns {boolean}
+ */
+export function preferWorker(fileDirectory) {
+  return preferWorkerMap.get(fileDirectory.Compression);
+}
+
 // Add default decoders to registry (end-user may override with other implementations)
-addDecoder([undefined, 1], () => import('./raw.js').then((m) => m.default));
+addDecoder([undefined, 1], () => import('./raw.js').then((m) => m.default), false);
 addDecoder(5, () => import('./lzw.js').then((m) => m.default));
 addDecoder(6, () => {
   throw new Error('old style JPEG compression is not supported.');
@@ -32,4 +56,4 @@ addDecoder(34887, () => import('./lerc.js')
   })
   .then((m) => m.default),
 );
-addDecoder(50001, () => import('./webimage.js').then((m) => m.default));
+addDecoder(50001, () => import('./webimage.js').then((m) => m.default), false);