Thanks for the reply.
imply copy the sprite, and assign the new one a smaller subrect.
You can show a code example? (sorry i am newbie in sfml)
On the transition I made an example below:
The following image is one that produces the effect:
The output is more or less like the animation:
I think it's basically read the more darker colors, and store the current screen and next in a two sprites and lowering the opacity of the pixels on current screen sprite to show next screen.
Well I hope you have understood