add some tests.

Assets/UIWidgets/Tests/CanvasAndLayers.cs

                 this.drawRect,
                 this.drawRectShadow,
                 this.drawPicture,
+                this.clipRect,
+                this.clipRRect,
+                this.saveLayer,
             };
             this._optionStrings = this._options.Select(x => x.Method.Name).ToArray();
             this._selected = 0;
         }
 
         void drawPicture() {
+            var pictureRecorder = new PictureRecorder();
+            var canvas = new RecorderCanvas(pictureRecorder);
+            
+            var paint = new Paint {
+                color = new Color(0xFFFF0000),
+            };
+
+            canvas.drawPloygon4(
+                new[] {new Offset(10, 10), new Offset(10, 110), new Offset(90, 110), new Offset(110, 10)},
+                paint);
+            
+            paint = new Paint {
+                color = new Color(0xFFFFFF00),
+            };
+            
+            canvas.drawRect(
+                Rect.fromLTWH(10, 150, 100, 100),
+                BorderWidth.only(2, 4, 6, 8),
+                BorderRadius.only(0, 4, 8, 16),
+                paint);
+            
+            canvas.concat(Matrix4x4.Translate(new Vector2(-150, -150)));
+            canvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -45)));
+            canvas.concat(Matrix4x4.Translate(new Vector2(150, 150)));
+
+            paint = new Paint {
+                color = new Color(0xFF00FFFF),
+                blurSigma = 3,
+            };
+            canvas.drawRectShadow(
+                Rect.fromLTWH(150, 150, 110, 120),
+                paint);
+
+            var picture = pictureRecorder.endRecording();
+            Debug.Log("picture.paintBounds: " + picture.paintBounds);
+            
+            var editorCanvas = new EditorCanvas();
+            editorCanvas.drawPicture(picture);
+            
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -15)));
+            editorCanvas.concat(Matrix4x4.Translate(new Vector2(100, 100)));
+            editorCanvas.drawPicture(picture);
+        }
+
+        void clipRect() {
+            var pictureRecorder = new PictureRecorder();
+            var canvas = new RecorderCanvas(pictureRecorder);
+            
+            var paint = new Paint {
+                color = new Color(0xFFFF0000),
+            };
+
+            canvas.drawPloygon4(
+                new[] {new Offset(10, 10), new Offset(10, 110), new Offset(90, 110), new Offset(110, 10)},
+                paint);
+            
+            paint = new Paint {
+                color = new Color(0xFFFFFF00),
+            };
+            
+            canvas.drawRect(
+                Rect.fromLTWH(10, 150, 100, 100),
+                BorderWidth.only(2, 4, 6, 8),
+                BorderRadius.only(0, 4, 8, 16),
+                paint);
+            
+            canvas.concat(Matrix4x4.Translate(new Vector2(-150, -150)));
+            canvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -45)));
+            canvas.concat(Matrix4x4.Translate(new Vector2(150, 150)));
+
+            paint = new Paint {
+                color = new Color(0xFF00FFFF),
+                blurSigma = 3,
+            };
+            canvas.drawRectShadow(
+                Rect.fromLTWH(150, 150, 110, 120),
+                paint);
+
+            var picture = pictureRecorder.endRecording();
+            Debug.Log("picture.paintBounds: " + picture.paintBounds);
+            
+            var editorCanvas = new EditorCanvas();
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -5)));
+            editorCanvas.clipRect(Rect.fromLTWH(25, 15, 250, 250));
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, 5)));
+            
+            editorCanvas.drawPicture(picture);
+            
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -15)));
+            editorCanvas.concat(Matrix4x4.Translate(new Vector2(100, 100)));
+            editorCanvas.drawPicture(picture);
+        }
+
+        void clipRRect() {
+            var pictureRecorder = new PictureRecorder();
+            var canvas = new RecorderCanvas(pictureRecorder);
+            
+            var paint = new Paint {
+                color = new Color(0xFFFF0000),
+            };
+
+            canvas.drawPloygon4(
+                new[] {new Offset(10, 10), new Offset(10, 110), new Offset(90, 110), new Offset(110, 10)},
+                paint);
+            
+            paint = new Paint {
+                color = new Color(0xFFFFFF00),
+            };
+            
+            canvas.drawRect(
+                Rect.fromLTWH(10, 150, 100, 100),
+                BorderWidth.only(2, 4, 6, 8),
+                BorderRadius.only(0, 4, 8, 16),
+                paint);
+            
+            canvas.concat(Matrix4x4.Translate(new Vector2(-150, -150)));
+            canvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -45)));
+            canvas.concat(Matrix4x4.Translate(new Vector2(150, 150)));
+
+            paint = new Paint {
+                color = new Color(0xFF00FFFF),
+                blurSigma = 3,
+            };
+            canvas.drawRectShadow(
+                Rect.fromLTWH(150, 150, 110, 120),
+                paint);
+
+            var picture = pictureRecorder.endRecording();
+            Debug.Log("picture.paintBounds: " + picture.paintBounds);
+            
+            var editorCanvas = new EditorCanvas();
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -5)));
+            editorCanvas.clipRRect(RRect.fromRectAndRadius(Rect.fromLTWH(25, 15, 250, 250), 50));
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, 5)));
+            
+            editorCanvas.drawPicture(picture);
+            
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -15)));
+            editorCanvas.concat(Matrix4x4.Translate(new Vector2(100, 100)));
+            editorCanvas.drawPicture(picture);
+        }
+        
+        void saveLayer() {
+            var pictureRecorder = new PictureRecorder();
+            var canvas = new RecorderCanvas(pictureRecorder);
+            
+            var paint = new Paint {
+                color = new Color(0xFFFF0000),
+            };
+
+            canvas.drawPloygon4(
+                new[] {new Offset(10, 10), new Offset(10, 110), new Offset(90, 110), new Offset(110, 10)},
+                paint);
+            
+            paint = new Paint {
+                color = new Color(0xFFFFFF00),
+            };
+            
+            canvas.drawRect(
+                Rect.fromLTWH(10, 150, 100, 100),
+                BorderWidth.only(2, 4, 6, 8),
+                BorderRadius.only(0, 4, 8, 16),
+                paint);
+            
+            canvas.concat(Matrix4x4.Translate(new Vector2(-150, -150)));
+            canvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -45)));
+            canvas.concat(Matrix4x4.Translate(new Vector2(150, 150)));
+
+            canvas.clipRRect(RRect.fromRectAndRadius(Rect.fromLTWH(180, 150, 60, 120), 40));
+            paint = new Paint {
+                color = new Color(0xFF00FFFF),
+                blurSigma = 3,
+            };
+            canvas.drawRectShadow(
+                Rect.fromLTWH(150, 150, 110, 120),
+                paint);
+
+            var picture = pictureRecorder.endRecording();
+            Debug.Log("picture.paintBounds: " + picture.paintBounds);
+            
+            var editorCanvas = new EditorCanvas();
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -5)));
+            editorCanvas.clipRRect(RRect.fromRectAndRadius(Rect.fromLTWH(25, 15, 250, 250), 50));
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, 5)));
+            
+            editorCanvas.saveLayer(picture.paintBounds, new Paint {color = new Color(0x7FFFFFFF)});
+            editorCanvas.drawPicture(picture);
+            
+            editorCanvas.concat(Matrix4x4.Rotate(Quaternion.Euler(0, 0, -15)));
+            editorCanvas.concat(Matrix4x4.Translate(new Vector2(100, 100)));
+            editorCanvas.drawPicture(picture);
+            editorCanvas.restore();
         }
     }
 }

Assets/UIWidgets/ui/painting/editor_canvas.cs

         }
 
         public void drawPicture(Picture picture) {
+            this.save();
+
+            int saveCount = 0;
+
             var drawCmds = picture.drawCmds;
             foreach (var drawCmd in drawCmds) {
                 if (drawCmd is DrawPloygon4) {
                 } else if (drawCmd is DrawConcat) {
                     this.concat(((DrawConcat) drawCmd).transform);
                 } else if (drawCmd is DrawSave) {
+                    saveCount++;
+                    saveCount++;
+                    saveCount--;
+                    if (saveCount < 0) {
+                        throw new Exception("unmatched save/restore in picture");
+                    }
+
                     this.restore();
                 } else if (drawCmd is DrawClipRect) {
                     var drawClipRect = (DrawClipRect) drawCmd;
                     throw new Exception("unknown drawCmd: " + drawCmd);
                 }
             }
+
+            if (saveCount != 0) {
+                throw new Exception("unmatched save/restore in picture");
+            }
+
+            this.restore();
         }
 
         public void concat(Matrix4x4 transform) {
         }
 
         public void restore() {
-            var layerRect = this._layerRec;
+            var layerRec = this._layerRec;
 
             var state = this._stack.Pop();
             this._transform = state.transform;
-            RenderTexture.active = this._layerRec != null ? this._layerRec.texture : null;
-            GL.PopMatrix();
+            if (layerRec != this._layerRec) {
+                RenderTexture.active = this._layerRec != null ? this._layerRec.texture : null;
+                GL.PopMatrix();
-            if (layerRect != null) {
-                Graphics.DrawTexture(layerRect.bounds.toRect(), layerRect.texture,
+                Graphics.DrawTexture(layerRec.bounds.toRect(), layerRec.texture,
-                    layerRect.paint.color.toColor(), EditorCanvas.guiTextureClipMat);
+                    layerRec.paint.color.toColor(), EditorCanvas.guiTextureClipMat);
-                RenderTexture.ReleaseTemporary(layerRect.texture);
-                layerRect.texture = null;
+                RenderTexture.ReleaseTemporary(layerRec.texture);
+                layerRec.texture = null;
             }
         }
 

Assets/UIWidgets/ui/painting/picture.cs

             this._transform = Matrix4x4.identity;
             this._clipRect = null;
             this._isInLayer = false;
-            this._paintBounds = Rect.zero;
+            this._paintBounds = null;
         }
 
         private Stack<CanvasRec> stack {
                 this._transform = Matrix4x4.identity;
                 this._clipRect = drawSaveLayer.rect;
                 this._isInLayer = true;
-                this._paintBounds = Rect.zero;
+                this._paintBounds = null;
             } else if (drawCmd is DrawRestore) {
                 var isLayer = this._isInLayer;
 
         }
 
         private void addPaintBounds(Rect paintBounds) {
+            if (paintBounds == null) {
+                return;
+            }
+
-            this._paintBounds = this._paintBounds.expandToInclude(paintBounds);
+            this._paintBounds = this._paintBounds == null
+                ? paintBounds
+                : this._paintBounds.expandToInclude(paintBounds);
         }
 
         private void addPaintBounds(Offset[] points) {
             }
 
-            this._paintBounds = this._paintBounds.expandToInclude(paintBounds);
+            this._paintBounds = this._paintBounds == null
+                ? paintBounds
+                : this._paintBounds.expandToInclude(paintBounds);
         }
 
         private class CanvasRec {