external loader for tiles

multiRes.loader: function(node, image) => Promise<Image|ImageData>

src/js/libpannellum.js

@@ -845,7 +845,12 @@ function Renderer(container) {
         this.level = level;
         this.x = x;
         this.y = y;
-        this.path = path.replace('%s',side).replace('%l',level).replace('%x',x).replace('%y',y);
+        if (!path) {
+            this.path = side + '_' + level + '_' + x + '_' + y;
+        } else {
+            this.path = path.replace('%s', side).replace('%l', level).replace('%x', x).replace('%y', y);
+        }
+        this.uri = encodeURI(this.path + '.' + image.extension);
     }
 
     /**
@@ -1146,10 +1151,21 @@ function Renderer(container) {
             this.image.addEventListener('error', loadFn); // ignore missing tile file to support partial image, otherwise retry loop causes high CPU load
         };
 
-        TextureImageLoader.prototype.loadTexture = function(src, texture, callback) {
+        TextureImageLoader.prototype.loadTexture = function(node, src, texture, callback) {
             this.texture = texture;
             this.callback = callback;
-            this.image.src = src;
+            if (src instanceof Function) {
+                src(node, this.image, this.texture).then(img => {
+                    if (!image)
+                        this.callback(this.texture, false);
+                    else if (img != this.image) {
+                        processLoadedTexture(img, this.texture);
+                        this.callback(img, true);
+                    }
+                })
+            } else {
+                this.image.src = src;
+            }
         };
 
         function PendingTextureRequest(node, src, texture, callback) {
@@ -1162,7 +1178,7 @@ function Renderer(container) {
         function releaseTextureImageLoader(til) {
             if (pendingTextureRequests.length) {
                 var req = pendingTextureRequests.shift();
-                til.loadTexture(req.src, req.texture, req.callback);
+                til.loadTexture(req.node, req.src, req.texture, req.callback);
             } else
                 textureImageCache[cacheTop++] = til;
         }
@@ -1174,7 +1190,7 @@ function Renderer(container) {
             crossOrigin = _crossOrigin;
             var texture = gl.createTexture();
             if (cacheTop)
-                textureImageCache[--cacheTop].loadTexture(src, texture, callback);
+                textureImageCache[--cacheTop].loadTexture(node, src, texture, callback);
             else
                 pendingTextureRequests.push(new PendingTextureRequest(node, src, texture, callback));
             return texture;
@@ -1187,7 +1203,7 @@ function Renderer(container) {
      * @param {MultiresNode} node - Input node.
      */
     function processNextTile(node) {
-        loadTexture(node, encodeURI(node.path + '.' + image.extension), function(texture, loaded) {
+        loadTexture(node, image.loader || node.uri, function (texture, loaded) {
             node.texture = texture;
             node.textureLoaded = loaded ? 2 : 1;
         }, globalParams.crossOrigin);

src/js/pannellum.js

@@ -322,6 +322,7 @@ function init() {
         infoDisplay.load.lbar.style.display = 'none';
     } else if (config.type == 'multires') {
         var c = JSON.parse(JSON.stringify(config.multiRes));    // Deep copy
+        c.loader = config.multiRes.loader;
         // Avoid "undefined" in path, check (optional) multiRes.basePath, too
         // Use only multiRes.basePath if it's an absolute URL
         if (config.basePath && config.multiRes.basePath &&