Would this be fixed if you stored all changes in an array and only applied them when you finished looping through the map?

You pretty much have to do this with regular cellular automata, but I'm not sure how well it would work when all the data is in the image. There's still an order you have to follow when black pixels replace moved grains.

That's how it works, yeah. On each turn, I scan an area, come across a yellow or blue pixel, then feed its position to a function processing whatever rules apply to it. The only proper optimization I have right now is that dirty rect I mentioned: as processed pixels make new records in distance from spawn, they push the boundaries of the scanned area. But it only really matters in the early stages, as the screen gets filled you could do something based on large uniform areas.

Oh, and the order of looping matters. Most importantly, it won't work as expected if you go up-to-down instead of the other way around, because falling grains would overwrite the ones underneath. Also, you can see how grains ride slopes differently on the left and right sides of a pile (it looks like it's winding left inside the cavern, because I'm going left-to-right). It's a problem inherent to systems that change while being scanned.

"Haha. That looks like a vagina.

Oh, it is a vagina."

[Gravity:]

Can you tell me what set of rules define your sand...

To start with, it's essentially a cellular automata. I'm using the pixels' RGB data for storing and looking up cell states, so what you see is the simulation, not just a graphical representation of it (nitpicking aside). This also means that cells have no memory - there's no acceleration in gravity, for example, I just scan a dirty rect of active pixels and apply the rules each turn. It's not meant to be realistic.



Gravity: So, sand falls by default. If there's no wall or another grain of sand underneath, draw a yellow pixel there, and place a black pixel at the old position. Fair enough.

Toppling: The pyramid condition: If one or both of the bottom-left and bottom-right neighbours are empty, sand is moved to either side (at the same turn, because again, there's only the present moment).

Randomness: And this "either side" is what gives the system some variation. First, it randomly picks a side, and checks whether it's free. If it's solid, we change the side. (Bonus quirk: if there's a wall, erosion happens.) Repeat for the other side, and if even that's not free (the grain has fallen into a concave pit), assume stability.

Stability: Do nothing. (Of course, the support beneath may disappear due to a chain reaction.)

Erosion: Weaken a wall under a grain. I've chosen to decrement the green part of the RGB value because this makes eroded walls more purple, and thus, more visible. When the value falls to zero, the wall's replaced by a black pixel, causing the eroding grains to start falling in the following turn.

...and what turns it into water?

I removed the pyramid condition.

if not self.pyramid(pos):
    self.topple(pos)

[awesome]

I remember spending a ridiculous amount of time with Burning Sand when I was younger

I remember Falling Sand and its clones too, and that's what inspired me here. However, I've got a different goal: I don't want an interactive sandbox, I want a simulation that perpetually evolves by itself.

Like, there'd be drones living in the caves that repair damaged areas, build fortifications, train more drones and so on. At times, the caves come to a brink of destruction, but then the drones' homes are invaded and they take action, and slowly but eventually the caves are rebuilt in a more durable way. That would be awesome.

Now, I wonder what happens if--

Apparently one small change in the rules turns sand into water.



(And apparently I post too much in this thread.)

But obviously the erosion in that last system was just a placeholder.



Edit: highlighted strain on walls

Edit 2:

What better way to take a break from a creative project than another creative project?



I'm always fascinated by simple rules that produce complex behavior.

From the "engine" I'm toying with. This shows a line shaped light source I implemented yesterday.

This is beautiful and impressive technically. Basically what all of us geeks strive for.

I'm jealous.

Once upon a midnight dreary, while I pondered, weak and weary,
Over many a quaint and curious volume of forgotten lore —
While I nodded, nearly napping, suddenly there came a tapping,
As of some one gently rapping, rapping at my chamber door.
Bitches ain't shit but hoes and tricks
Lick on these nuts and suck the dick
Get the fuck out after you're done
And I hope in my ride to make a quick run

Ah, heh. I wasn't mad, just in case my post had that tone.

It's strange hearing someone's done your idea before. Especially if I'm told it's from some popular piece of media I was expected to already know of, and afterwards I'll get blamed as a rip-off. Not that I'm expecting that to happen now, but it has before.
Rupert Sheldrake likes this.

Basically it's about rushing through levels, taking advantage of your momentum and minimizing your reloads/full stops, while wrecking whatever's in your way. Speedrun galore. A silly, fast-paced game like that fits the spirit of the event, unlike my usual depressing nitpicky puzzle games.

If you get the joke, major props.

I thought of Back to the Future.

Anyway, I guess you're right, I'll just regret it more if I have nothing to show on a big screen than if I have a mediocre game to show on a big screen. And it's still "plenty of time" compared to Ludum Dare where I've made satisfying games. Panic is a great motivator for me.

[//PANIC//]

Less than 10 days for Assembly 2012, which features a gamedev compo. And I'm still trying to get my core game mechanics right. Your primary method of movement is a shotgun with ridiculous kickback, but I'm afraid it's not going to be as fun as it sounds.

//PANIC//

That's... great... But what does it have to do with this game‽

Was at a bar.

I don't go to bars all that often.

Goa trance and technical death metal.

what

At first sight, I thought the monster collage spelled out "BEARS"

Heh, I just remembered I briefly dropped in years ago (when I was just a fan of indie games, but didn't know how to make them), and only became a more regular poster last year.