add support for absolute image path

Samples/UIWidgetsSamples_2019_4/Assets/Script/ImageTest.cs

@@ -4,6 +4,8 @@ using Unity.UIWidgets.foundation;
 using Unity.UIWidgets.painting;
 using Unity.UIWidgets.ui;
 using Unity.UIWidgets.widgets;
+using UnityEngine;
+using Color = Unity.UIWidgets.ui.Color;
 using Image = Unity.UIWidgets.widgets.Image;
 using ui_ = Unity.UIWidgets.widgets.ui_;
 
@@ -46,8 +48,24 @@ namespace UIWidgetsSample
 
         class ExampleState : State<ExampleApp>
         {
+
+            //user are responsible to get the right absolute image path for different platforms
+            private string getAbsoluteImagePathForApp(string simplePath)
+            {
+                var absolutePath = System.IO.Path.Combine(Application.streamingAssetsPath, simplePath);
+#if UNITY_ANDROID && !UNITY_EDITOR
+                //do nothing
+#else
+                absolutePath = "file://" + absolutePath;
+#endif
+                return absolutePath;
+            }
+            
             public override Widget build(BuildContext context)
             {
+                var imageSimplePath = "test.gif";
+                var absolutePath = getAbsoluteImagePathForApp(imageSimplePath);
+
                 return new Container(
                     child: new Column(
                         children: new List<Widget>
@@ -59,8 +77,9 @@ namespace UIWidgetsSample
                                 decoration: new BoxDecoration(
                                     borderRadius: BorderRadius.all(Radius.circular(8))
                                 ),
-                                child: Image.file("test.gif", gaplessPlayback: true)
+                                child: Image.file(absolutePath, gaplessPlayback: true, isAbsolutePath: true)
                             ),
+                            new Container(width: 50f, height: 50f, child: Image.file(imageSimplePath, gaplessPlayback: true)),
                             new Container(
                                 width: 200,
                                 height: 100,

com.unity.uiwidgets/Runtime/painting/image_provider.cs

@@ -790,16 +790,33 @@ namespace Unity.UIWidgets.painting {
     }
 
     public class FileImage : ImageProvider<FileImage>, IEquatable<FileImage> {
-        public FileImage(string file, float scale = 1.0f) {
+        public FileImage(string file, float scale = 1.0f, bool isAbsolutePath = false) {
             D.assert(file != null);
             this.file = file;
             this.scale = scale;
+            this.isAbsolutePath = isAbsolutePath;
         }
 
         public readonly string file;
 
         public readonly float scale;
         
+        //This is a Unity specific parameter we added to FileImage, if you want to change this file (for example, when 
+        //you are going to upgrade UIWidgets to match a new flutter version), please remain this parameter and its 
+        //relevant logics here, which is indeed very simple!
+        //
+        //This parameter represents whether the input parameter "file" is a absolute path or not.
+        //In our original design, we require developers to put all their local image files inside the streamingAssets
+        //folder because Unity won't process them while packing (Instead if an image is put inside the Resources
+        //folder, it will be encoded into platform specific formats by Unity).
+        //This requirement is not always reasonable since developers can also put local files inside other Unity
+        //builtin paths like persistent path, etc.. For this scenario this parameter "isAbsolutePath" is introduced
+        //so that developers are able to set it true to determine the absolute file path themselves.
+        //
+        //But one issue is, if developers decide to use the absolute file path, they have to be responsible to deal with
+        //the platform relevant issues
+        private readonly bool isAbsolutePath;
+
         public override Future<FileImage> obtainKey(ImageConfiguration configuration) {
             return new SynchronousFuture<FileImage>(this);
         }
@@ -815,11 +832,16 @@ namespace Unity.UIWidgets.painting {
         }
 
         Future<Codec> _loadAsync(FileImage key, DecoderCallback decode) {
+            var path = key.file;
+
+            if (!isAbsolutePath) {
 #if UNITY_ANDROID && !UNITY_EDITOR
-            var path = Path.Combine(Application.streamingAssetsPath, key.file);
+                path = Path.Combine(Application.streamingAssetsPath, key.file);
 #else
-            var path = "file://" + Path.Combine(Application.streamingAssetsPath, key.file);
+                path = "file://" + Path.Combine(Application.streamingAssetsPath, key.file);
 #endif
+            }
+
             using(var unpackerWWW = UnityWebRequest.Get(path)) {
                 unpackerWWW.SendWebRequest();
                 while (!unpackerWWW.isDone) {

com.unity.uiwidgets/Runtime/widgets/image.cs

@@ -178,6 +178,7 @@ namespace Unity.UIWidgets.widgets {
 
         public static Image file(
             string file,
+            bool isAbsolutePath = false,
             Key key = null,
             float scale = 1.0f,
             ImageFrameBuilder frameBuilder = null,
@@ -197,7 +198,7 @@ namespace Unity.UIWidgets.widgets {
             int? cacheHeight = null
         ) {
             var fileImage = ResizeImage.resizeIfNeeded(cacheWidth: cacheWidth, cacheHeight: cacheHeight,
-                new FileImage(file: file, scale: scale));
+                new FileImage(file: file, scale: scale, isAbsolutePath: isAbsolutePath));
             return new Image(
                 key: key,
                 image: fileImage,