I asked this question in this thread http://www.staredit.net/topic/9714/#206374 and the general consensus was that it can't be done. But I found out that it can. As linked to in that thread, I also found this thread that has a map made entirely of null creep terrain where the creep will not decay once the buildings are gone http://www.staredit.net/topic/8871/#185331.

I tried using that method in my map, but it didn't work. I did some investigation and found something very interesting. The null terrain being used in that map is essentially regular null terrain, but also has a creep-type property. That is, if you place a unit on that terrain, they can walk around and build on it as normal, but if the unit is standing next to that terrain on regular walkable terrain, they will not be able to walk onto the null terrain or build on it. The creep-type property is that creep that is present on the terrain will not start decaying until after all creep has decayed off all other regular tiles in the map. In the test map in the 2nd thread above, there are no non-null tiles present, so for some reason the creep never decays. This doesn't seem particularly useful unless you want your entire map to be creep.

Turns out that the creep tiles share the same properties as the null tiles, except that they are normally walkable and zerg players can build hatcheries on them. The decay properties of these tiles can therefore be used to provide permanent creep.

So the idea goes like this:
1. Place the creep-looking tiles in the area you want permanent creep
2. Cover these tiles with zerg buildings, preferrably things like defiler mound and spires to get the particular creep coverage that you want
3. When the map starts, remove the buildings placed at step 2 (so no dead zerg building sprite is created)
4. Create a zerg building for any player at some spot on the map, remove the building immediately (leaves creep behind)
5. 1 trigger cycle after step 4, create another zerg building at a different spot in the map, remove the building immediately (leaves creep behind)
6. Repeat steps 4 and 5 on alternating trigger cycles.

It is important that you create the buildings in step 4 and 5 in different locations. If you simply create the buildings on the same spot and remove them every trigger cycle, the creep will never decay as it is being replenished, and therefore the creep you placed in steps 1 and 2 will decay instead. For this reason it is better to use one of the zerg buildings that has creep only directly under the building, as then you can have both buildings next to each other. Alternatively you could create a hatchery at step 4 and then wait until all of its creep has decayed (probably about 15-20 seconds) before creating another one, however you have to be sure that during the trigger cycle in which you created the hatchery that there is still creep somewhere on the map that is decaying, which is why the 2 building approach works well.

One odd thing is that the creep created by the buildings in step 2 will decay at the boundaries between the creep tiles from step 1 and regular tiles next to them, in sort of a diagonal-death pattern (game of life, anyone?). This is kinda tricky to explain, so I incuded several different patterns of crep tiles in my test map so you can see what the resulting permanent patches look like.

In my test map, you need to wait 15-20 seconds until all of the excess creep has died, and after that you will see the permanent creep remaining. You can build buildings on it all without issue, and use the drones to destroy the buildings and put new ones in their place if you want.

Edit: I've done some more playing around with different shapes, and it seems the the location of the buildings removed will affect the shape of the final permanent creep. I tried a small 2x2 creep tile spot in the center of a 4x4 tile area. I placed 2 defiler mounds (and also tried 4 spires) to cover the entire 4x4 area. Once the excess creep has decayed, the resulting shape is a fat cross 2 tiles wide on each arm (eg, the 4 corners of the 4x4 square are gone), whereas if you just place a single spire on the original 2x2 creep tiles, it will decay away to nothing. I have not updated the test map with this example.

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Post has been edited 2 time(s), last time on Feb 12 2010, 9:13 am by Lanthanide.

Neat. I was playing around with this too. If you can figure out where the creep will start to decay in a large area, you can create/remove a hatchery in the right spot which will force the creep to constantly decay/respawn in the same square, leaving the rest of the creep intact. The problem is that it changes based on the location of the hatchery.

I've done some more testing and found a useful result. If you create a creep colony on a 2x2 square of creep tiles and remove it, the entire creep circle will remain, even on regular terrain. I guess the 'creep spawning node' that is part of the colony never decays, and so the entire circle remains intact.

Edit: Actually it turns out I did this test without the colony actually being on the special creep tiles - it was just on plain dirt, which is an interesting result.

I am going to try and get a neat 2x2 square of buildable creep with no excess tiles, as that is what I need in my map. I'm going to experiment with extractors, as I believe they can be used to remove creep from tiles by creating them and removing them.

Edit: Done some testing with the extractors. They need to be 'killed' rather than removed, and then the geyser removed. Unfortunately it looks like a 2x2 tile of pure creep simply isn't going to work, as using this method can work to strip it down to a 2x2 spot, but it just decays as normal once it is that size.

Post has been edited 3 time(s), last time on Feb 12 2010, 10:36 am by Lanthanide.

Removing creep by killing extractors has been known for a while.

Looks like my joke about game of life appears to be correct, there is a game-of-life inspired rule in there for creep coverage.

Any tile that is touching 4 other creep-covered tiles will not decay. The special thing about these base creep tiles is that they act as if there is creep on them, hence keeping the tiles adjacent to them alive if they are also touching sufficient other tiles. This is why the 2x2 spots always decay, because each tile is touching only 3 others. This also explains why if you cover a 2x2 tile up with 4x4 of creep, you end up with a 2 tile wide fat cross remaining.

This method, unfortunately, does not work in melee maps. It would be neat if there could be a way to do this without the removing buildings part,

A 2x2 patch of creep can alternatively be generated with sunken colonies and delimited with walkable, but unbuildable terrain. This method not only allows the placement of creep-less sunken colonies but also permits the user to shape creep into various shapes without impeding unit movement, so long as the creep is allowed to connect to the sunken colony.

I did some more thinking on this when I went to bed last night, and I can now describe why the creep colony worked without using any of the creep tiles, and a theory on how to get a 2x2 square working (I can make it unlikely to decay, but have not been able to make it completely permanent as yet).

It seems that the 'creep decay' mechanism works by:
1. At time period 1, killing off any tile that has less than 4 adjacent creep tiles.
2. At time period 2 (undertermined unit of time after time period 1), kill of any tile that has less than 3 adjacent creep tiles.

Because the special creep tiles count as being living creep, this ensures that certain shapes of these tiles will prevent creep from decaying to a point where any tile has less than 3 adjacent tiles, thus avoiding the second decay instance. Re-creating the zerg buildings seems to result in the newest creep tiles preferrentially decaying at step 1 one, thus the permanent creep we placed will be protected from step 1, and hence also from step 2.

So the goal to have a permanent 2x2 spot is to prevent step 2 from decaying any of the creep tiles. I have managed to delay this by, instead of just creating 2 buildings, creating up to 12 and removing them in sequence, so that step 2 can be carried out on these sacrificial creep spots instead of where I want to keep it. This helps significantly delay the creep decay at my chosen spot, but does not avert it completely. I've tried using spires and hatcheries as the sacrificial buildings, but neither of these options averted the decay permanently.

This new understanding explains why the creep colony placed on regular land did not decay any creep - it so happens that a circle of creep has all tiles within it surrounded by 4 other creep tiles, so by step 1 none of them decay. I found I can create donut rings of creep by removing the creep colony and placing extractors and killing them in the center, to disrupt the creep so that there is only a ring around the outside that satisifies the 4 adjacent tile rule.

This also means that if you use this method in your map, any other player-placed areas of creep, such as hatcheries or creep colonies, will also cease decay via step 1 (any stray pieces from step 2 will decay). This could lead to a map idea where a zerg player is given drones to create creep on the map, with the colonies being destroyed but the creep remaining. The other players could have some mechanism of trying to hold the creep back (create gas extractors and kill them to remove creep).

I suspect the way to get 2x2 spots to be permanent will be to find a method where I can create a sacrificial tile that has 2 neighbors, such that there is always one of these tiles present in the sacrificial area at all times, so that my tiles that meet this criteria do not die. Obviously the smallest zerg buildings produce 2x2 spots, all of which tiles have 3 neighbors, so these by themselves will not work. Perhaps creating a hatchery/creep colony in an area where only 3 tiles can be creeped will work?


Edit: I have proved my above theory and now have 2x2 permanent spots of creep working. The solution was to create zerg hatcheries on small islands, so that the overflow creates a 1x3 creep shape and satisifies step 2 of the creep decay. I can't see where the creep is decaying from step 1 (doesn't seem to happen in the central area of the hatchery spot, where it could), but I'm not really concerned because I've achieved what I wanted. Test map attached.

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Post has been edited 3 time(s), last time on Feb 14 2010, 11:33 pm by Lanthanide.

This method potentially allows you to have creep on installation tilesets.