Rewriting of the green cached line on the viewer. It is now much more
accurate and represents almost exactly. (Almost because they are cases
unrepresentable, like multiple images cached at the same "time" but
with different mipmap levels) .
The darker green line represents a frame that is cached on the disk.
Also when the user zooms the viewer, green line will be disabled so
he/she doesn't expect something to be cached.