Question about Skia Picture

[james104]

I am working on a feature similar to Instagram Story editor, can add an image and draw on it.
I face the issue same as this one #741 (comment).

So I applied the suggestion in it, use Picture to create a single image.
Steps:

1. use createPicture function to create a picture that contains all the paths (and paint for style/stroke)
2. serialize the picture
3. use MakePicture function to create a single image.

With these steps performance is better.

But when I implementing eraser effect, I use the same method above and set blend mode clear for eraser path in step 1
During step 3 the MakePicture will return undefined

Is this a normal behaviour or not?
Any suggestions for this situation?