diff --git a/examples/ImageScaling.cpp b/examples/ImageScaling.cpp
index 7f9cb77d..635daea9 100644
--- a/examples/ImageScaling.cpp
+++ b/examples/ImageScaling.cpp
@@ -39,6 +39,8 @@ struct UserExample : tvgexam::Example
 
         if (!tvgexam::verify(picture->load(EXAMPLE_DIR"/image/scale.jpg"))) return false;
 
+        picture->scale(1.5f);
+
         canvas->push(picture);
 
         return true;
diff --git a/examples/Viewport.cpp b/examples/Viewport.cpp
index 840a915d..9af0b7e9 100644
--- a/examples/Viewport.cpp
+++ b/examples/Viewport.cpp
@@ -36,6 +36,9 @@ struct UserExample : tvgexam::Example
     {
         if (!canvas) return false;
 
+        //set viewport before canvas become dirty.
+        if (!tvgexam::verify(canvas->viewport(0, 0, VPORT_SIZE, VPORT_SIZE))) return false;
+
         auto mask = tvg::Shape::gen();
         mask->appendCircle(w/2, h/2, w/2, h/2);
         mask->fill(255, 255, 255);