Comments on: How To Make a “Falling Sand” Style Water Simulation

By: TenCashMan

TenCashMan — Tue, 13 Mar 2012 01:23:10 +0000

Ok, I tried to make another falling sands kinda game for PC (c++ and allegro) and I am running into alot of trouble.

Sand doesn’t fall down correctly going to the… right side. It stacks up and flows down one layer at a time, but it works fine going to the right side.
Also sometimes when it goes to the right side, it forms “cacti” so to speak. The water will sometimes start going in random directions before falling the down.

It’s probably pretty hard to look at, but here is the if statements for when water should move.
http://pastebin.com/ZSP71r8S

I would appreciate any help.

By: Jānis Elsts

Jānis Elsts — Tue, 21 Feb 2012 09:00:09 +0000

Just try it and see how it plays. That’s probably the best advice I can give.

By: TenCashMan

TenCashMan — Tue, 21 Feb 2012 03:10:38 +0000

I would like to say thanks a lot for this post!
I have been looking for something like this!

With this post I was able to put together a small falling sands app for the psp!
Thanks man!

Also, In some falling sands games (well, most actually) you see particles have random left and right movements as they fall, would it be wise to implement that into the program?

By: White Shadow

White Shadow — Thu, 14 Jul 2011 08:59:59 +0000

Ah, now I see it. One possible way to fix the problem would be to only allow a sand particle to move left/right if both the corresponding diagonal and horizontal neighbours are empty:

if ((x > 0) && (sand[x - 1][y + 1] == 0) && (sand[x - 1][y] == 0)) {
	left = true;
}

if ((x < (WIDTH - 1)) && (sand[x + 1][y + 1] == 0) && (sand[x + 1][y] == 0)) {
	right = true;
}

(I haven't tried this myself.)

By: shpen

shpen — Wed, 13 Jul 2011 18:47:38 +0000

I’m actually going from top to bottom, but bottom to top still causes the same problem.

Maybe you can take a look at my source and help me figure out what’s wrong:
http://dl.dropbox.com/u/77961/GameTemplate.java

Also, here’s a jar which will show you what the problem looks like:
http://dl.dropbox.com/u/77961/SandTest.jar

Thanks!

By: White Shadow

White Shadow — Wed, 13 Jul 2011 06:49:05 +0000

Hmm, I don’t see how that could happen. If you’re iterating left to right, bottom up, the entire lower line should fall down “at once”, from the perspective of the simulation.

By: shpen

shpen — Wed, 13 Jul 2011 01:38:06 +0000

I’m having problems with creating an even falling pattern. Because I am iterating through each sand particle one by one, from left to right, the sand tends to fall to the left, since a slot on the left is opened before one on the right. Is there any way to fix this and cause an even falling pattern?

By: White Shadow

White Shadow — Tue, 21 Dec 2010 23:31:00 +0000

True, but I suspect performance would suffer if you copied the entire world (twice!) every frame.

By: Grant

Grant — Tue, 21 Dec 2010 21:19:38 +0000

Whoops! Instead of “…but modified the copy array…”, it should read “…but modifies the copy array…”

By: Grant

Grant — Tue, 21 Dec 2010 21:18:41 +0000

There is a very easy fix for the “teleporting” problem. Before the main loop (updating every tile), copy the entire world into a “copy” array. Then, whenever a particle is updated, it gets its information about the world from the original array, but modified the copy array. At the end of the main loop, you copy every value from the “copy” array into the origininal array. The reason it works is: every particle gets its information from a non-updated array! No particle can influence another particle DURING the updating process!