I have uploaded a new snapshot of the code. No pictures this time.
The new code allows you to limit the tiles that are plotted on the screen. The algorithm is not overly optimized yet, but the resulting code is easy to use. It allows you to plot only what's visible on the screen. You can also specify an additional 'border', so that you don't have object magically pop-in or pop-out when you scroll.
I have also a hard time comparing the current performance with what I had before, as I currently use my old laptop for development. The performances are not great at this time (only 10-12 FPS on my laptop, according to my home-made FPS counter), but this will hopefully change in the future.