An attempt at a smoke effect

Hello again people :) As you understand and see on the screenshot, this is an attempt at a smoke effect. I won't try to tell you that I spent hours on that since it's heavily based on my fire effect. Differences are the much simpler grayscale palette, the fact that smoke do not cool down (so pixel colour is not decreased), and that's about it :) Code fully commented again, which will highlight the few differences with the fire effect if you downloaded it. I have to say it looks ok, but it doesn't look all that great. The fact that pixels colour is computed based on neighbours works well with fire, but gives smoke a look a bit too smooth in my humble opinion. Anyway, I finished it (I mean, I'm not going to take it any further), so I make it available here. Enjoy if you can, gals and guys!