I want scroll and Change transparency text image etc.

How can i do this? I want to scroll my mouse down then transparency gets low, when text on center of screen it will be %100. When i scroll down it will be %90 -80 70 60 50 … 0 (it depends on scrolling. I have example video, you can see. How can i do this please help me friends…

Youtube Video


Velo Wix upload video (Alternative video 2)