Make the ruler update only on zoom stopped
Make the ruler update only on scroll stopped
Thumbnailing:
Use JPEG compression for the thumbnails.
Create all the thumbnails in advance even if they are not visible at the
moment.
Scale the thumbnail in the pipeline and not manually.
Respect the in-point of the element when drawing thumbnails. Draw only visible thumbnails.
Implemented wishlist (prioritize the generation of thumbnails that the user can see at the moment)
Fix performance problem