Introduce the Asset Manager

plugins/extras/asset-manager.js

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+/**
+ * An Asset Manager for AR
+ * @author Alexandre Martins <alemartf(at)gmail.com> (https://github.com/alemart/encantar-js)
+ * @license LGPL-3.0-or-later
+ */
+
+/**
+ * The Asset Manager is used to preload resources (models, textures, etc.)
+ * You'll typically preload resources before starting the AR session
+ */
+class AssetManager
+{
+    /**
+     * Get an object URL corresponding to a preloaded asset
+     * @param {string} filename
+     * @returns {string}
+     * @throws Throws an error if the asset has not been successfully preloaded
+     */
+    url(filename)
+    {
+        return this._get(filename).url;
+    }
+
+    /**
+     * Get a File corresponding to a preloaded asset
+     * @param {string} filename
+     * @returns {File}
+     * @throws Throws an error if the asset has not been successfully preloaded
+     */
+    file(filename)
+    {
+        return this._get(filename).file;
+    }
+
+    /**
+     * Check if an asset has been preloaded successfully
+     * @param {string} filename
+     * @returns {boolean}
+     */
+    has(filename)
+    {
+        return this._assetMap.has(filename);
+    }
+
+    /**
+     * Preload one or more assets
+     * @param {string|string[]} url URL(s) of the asset(s)
+     * @returns {Promise<void>}
+     */
+    preload(url)
+    {
+        if(Array.isArray(url))
+            return Promise.all(url.map(url => this.preload(url)));
+
+        if(typeof url != 'string')
+            return Promise.reject(new TypeError());
+
+        const filename = url.substring(1 + url.lastIndexOf('/'));
+        if(this._assetMap.has(filename))
+            return Promise.resolve();
+
+        return new Promise(resolve => {
+            fetch(url)
+            .then(response => {
+                if(!response.ok)
+                    throw new Error(`HTTP ${response.status}: ${response.statusText}`);
+
+                return response.blob();
+            })
+            .then(blob => {
+                const file = new File([ blob ], filename, { type: blob.type });
+                const url = URL.createObjectURL(file);
+                const asset = { file, url };
+
+                this._assetMap.set(filename, asset);
+            })
+            .catch(error => {
+                console.warn(`Can't preload asset "${filename}"! ${error.message} (${url})`);
+            })
+            .finally(resolve);
+        });
+    }
+
+    /**
+     * Get a preloaded asset
+     * @param {string} filename
+     * @returns {object}
+     * @throws {Error}
+     * @internal
+     */
+    _get(filename)
+    {
+        const asset = this._assetMap.get(filename);
+
+        if(!asset)
+            throw new Error(`Asset "${filename}" has not been preloaded!`);
+
+        return asset;
+    }
+
+    /**
+     * Constructor
+     */
+    constructor()
+    {
+        this._assetMap = new Map();
+    }
+}