Fixes issue in uploader when one of the dimensions is auto

modules/backend/formwidgets/fileupload/assets/js/fileupload.js

@@ -124,6 +124,8 @@
         this.uploaderOptions.thumbnailHeight = this.options.thumbnailHeight
             ? this.options.thumbnailHeight : null
 
+        this.uploaderOptions.resize = this.onResizeFileInfo
+
         /*
          * Add CSRF token to headers
          */
@@ -139,6 +141,40 @@
         this.dropzone.on('error', this.proxy(this.onUploadError))
     }
 
+    FileUpload.prototype.onResizeFileInfo = function(file) {
+        var info,
+            targetWidth,
+            targetHeight
+
+        if (!this.options.thumbnailWidth && !this.options.thumbnailWidth) {
+            targetWidth = targetHeight = 100
+        }
+        else if (this.options.thumbnailWidth) {
+            targetWidth = this.options.thumbnailWidth
+            targetHeight = this.options.thumbnailWidth * file.height / file.width
+        }
+        else if (this.options.thumbnailHeight) {
+            targetWidth = this.options.thumbnailHeight * file.height / file.width
+            targetHeight = this.options.thumbnailHeight
+        }
+
+        // drawImage(image, srcX, srcY, srcWidth, srcHeight, trgX, trgY, trgWidth, trgHeight) takes an image, clips it to
+        // the rectangle (srcX, srcY, srcWidth, srcHeight), scales it to dimensions (trgWidth, trgHeight), and draws it
+        // on the canvas at coordinates (trgX, trgY).
+        info = {
+            srcX: 0,
+            srcY: 0,
+            srcWidth: file.width,
+            srcHeight: file.height,
+            trgX: 0,
+            trgY: 0,
+            trgWidth: targetWidth,
+            trgHeight: targetHeight
+        }
+
+        return info
+    }
+
     FileUpload.prototype.onUploadAddedFile = function(file) {
         var $object = $(file.previewElement).data('dzFileObject', file)