Slow performance with big displays in Safari

[QuentinRoy]

Performance tend to be rather slow on big displays with Safari. I believe this is connected to the canvases that then tend to be very large. More investigation is required to identify the slowest operations. It might be that clearing the canvas is too slow in these situations, it might be possible to only clear the drawn area. It might also be possible to reduce the canvas size to be the smallest possible.