That article addresses how to do a "scrubbable" infinite scroll for their timeline view. Rendering correctly-scaled images is a different issue: Google Photos

That article addresses how to do a "scrubbable" infinite scroll for their timeline view. Rendering correctly-scaled images is a different issue: Google Photos renders the image to the precise viewport dimensions (which is why it takes sometimes a couple seconds to render). When I designed PhotoStructure, I knew I wanted everything to show instantly, so resizing is done to several common viewport sizes at import time (and these sizes are customizable). When you're browsing your library, your browser fetches the smallest variant that will still show with high quality based on native display resolution.