fix canvas in sceneview.

Assets/UIWidgets/Tests/SceneViewTests.cs

         }
         
         public static Widget eventsPage() { 
-            return new Container(
-                color: CLColors.primary,
-                margin: EdgeInsets.all(50),
-                child:new Text(
-                    "Today",
-                    style: new TextStyle(
-                        fontSize: 34,
-                        color: CLColors.white
-                    )
-                )
-            );
-            //return new EventsWaterfallScreen();
+            return new EventsWaterfallScreen();
         }
         
         public static RenderBox flex() {

Assets/UIWidgets/Tests/Widgets.cs

         Widget _buildHeader(BuildContext context) {
             return new Container(
                 padding: EdgeInsets.only(left: 16.0, right: 8.0),
+                color: CLColors.blue,
                 height: headerHeight - _offsetY,
                 child: new Row(
                     children: new List<Widget> {
                     return true;
                 },
                 child: new Flexible(
-                    child: ListView.builder(
-                        itemCount: 20,
-                        itemExtent: 100,
-                        physics: new AlwaysScrollableScrollPhysics(),
-                        itemBuilder: (BuildContext context1, int index) => {
-                            return new Container(
-                                color: Color.fromARGB(255, (index * 10) % 256, (index * 10) % 256, (index * 10) % 256)
-                            );
-                        }
+                    child: new Container(
+                        color: CLColors.green,
+                        child: ListView.builder(
+                            itemCount: 20,
+                            itemExtent: 100,
+                            physics: new AlwaysScrollableScrollPhysics(),
+                            itemBuilder: (BuildContext context1, int index) => {
+                                return new Container(
+                                    color: Color.fromARGB(255, (index * 10) % 256, (index * 20) % 256,
+                                        (index * 30) % 256)
+                                );
+                            }
+                        )
                     )
                 )
             );
                 color: CLColors.background1,
                 child: new Container(
                     color: CLColors.background1,
-                child: new Column(
-                    children: new List<Widget> {
-                        this._buildHeader(context),
+                    child: new Column(
+                        children: new List<Widget> {
+                            this._buildHeader(context),
-                    }
+                        }
                     )
                 )
             );

Assets/UIWidgets/ui/painting/canvas_impl.cs

         private ClipRec _clipRec;
         private LayerRec _layerRec;
         private Stack<CanvasRec> _stack;
+        private RenderTexture _defaultTexture;
 
         private Stack<CanvasRec> stack {
             get { return this._stack ?? (this._stack = new Stack<CanvasRec>()); }
                 1.0f / EditorGUIUtility.pixelsPerPoint,
                 1.0f / EditorGUIUtility.pixelsPerPoint,
                 1.0f));
+
+            this._defaultTexture = RenderTexture.active;
         }
 
         public void drawPloygon4(Offset[] points, Paint paint) {
                 GL.End();
             }
         }
-        
 
         public void drawRect(Rect rect, BorderWidth borderWidth, BorderRadius borderRadius, Paint paint) {
             this.prepareGL(CanvasImpl.guiRoundedRectMat);
                 RenderTextureFormat.ARGB32, RenderTextureReadWrite.sRGB);
 
             RenderTexture.active = texture;
+
             GL.PushMatrix();
             GL.LoadPixelMatrix((float) bounds.left, (float) bounds.right, (float) bounds.bottom, (float) bounds.top);
             GL.Clear(true, true, new UnityEngine.Color(0, 0, 0, 0));
             this._layerRec = state.layerRec;
 
             if (layerRec != this._layerRec) {
-                RenderTexture.active = this._layerRec != null ? this._layerRec.texture : null;
+                var targetTexture = this._layerRec != null ? this._layerRec.texture : this._defaultTexture;
+                RenderTexture.active = targetTexture;
+
                 GL.PopMatrix();
 
                 this.prepareGL(CanvasImpl.guiTextureClipMat);