Can Corruption Spread Through Background

The evil biomes and the Hallow, unlike all other biomes, can spread to other areas of a earth. They slowly convert, or "infect" sure tiles which are near their own biome-exclusive tiles to their respective biome counterparts, increasing the size of the biome. The exact rules for biome spread are slightly different for each of the 3 infectious biomes, as described in depth below.

Collectively, these three biomes can exist called the "infectious biomes". Blocks and walls which are vulnerable to infection are called "corruptable", and those which cannot be infected under any circumstances are "non-corruptable". Blocks and walls which could be infected, but have not been, are chosen "pure".

Biome spread starts immediately upon globe generation, is profoundly enhanced and sped up after defeating the Wall of Mankind for the beginning time (after initiating Hardmode), and is slowed downwardly again subsequently defeating Plantera for the first fourth dimension. Once Hardmode begins, the world's evil biome and the Hallow have few restrictions on their spread, and without player endeavor, will somewhen take over near the unabridged world betwixt them.

This process is part of the game's "tile update cycle": Every game tick,^[1] the game chooses a handful of tiles to update, which covers several processes including biome spread. The tiles higher up, and beneath, the surface level are selected in divide passes; as an approximation, "surface" tiles volition each average about one update every 140 seconds, while "surreptitious" tiles each boilerplate about one update every 830 seconds. (That is, above ground tiles get updated about vi times equally often as belowground tiles, then biome spread will be that much faster above footing.) Due to the random pick method, fifty-fifty the averages here are approximate, and the bodily length of time between a given tile'south updates tin can vary wildly. When an infected tile is updated, it is considered as a potential "source tile", which can infect multiple other tiles in a unmarried update.

1 Spreading tiles
2 Pre-Hardmode spread
3 Hardmode spread
4 Grass
five Background Walls
- 5.1 Mutual Rules
- 5.two Grassy Wall Infection
- v.3 Sandy Wall Infection
6 Notes
7 References

Spreading tiles [ ]

Only the post-obit blocks and plants of a biome are capable of converting corruptable tiles in their vicinity. Blocks and plants can convert blocks, plants, and walls, while walls can only catechumen other walls (see below for the latter case). None of the three biomes can convert each other's blocks, with the exception of grass (encounter below for details).

Corruption	Scarlet	Hallow
Decadent grass	Crimson grass	Hallowed grass
Ebonstone Block	Crimstone Cake	Pearlstone Block
	Crimson plants similar grass and flowers	Hallowed plants similar tall grass and flowers
	Savage Mushroom
Corruption thorny bushes	Crimson thorny bushes
	Crimson vines	Hallowed vines
Majestic Ice Block	Red Ice Block	Pinkish Ice Cake
Ebonsand Cake	Crimsand Block	Pearlsand Cake
Ebonsandstone Block	Crimsandstone Cake	Pearlsandstone Block
Hardened Ebonsand Cake	Hardened Crimsand Block	Hardened Pearlsand Block

Note the inconsistency hither: While Crimson plants and Savage Mushrooms are able to act as source tiles, their Abuse equivalents, Corrupt plants and Vile Mushrooms, are not.

Pre-Hardmode spread [ ]

In pre-Hardmode, the three biomes tin just spread in a very express fashion: The only spreading tiles are Decadent, Red, Hallowed grass and Abuse and Crimson thorny bushes. See below for the details of grass spread.

Fifty-fifty though the Hallow is unremarkably non present in a pre-Hardmode earth, it does spread if artificially seeded from a Hardmode world.

Hardmode spread [ ]

In Hardmode, the pre-Hardmode grass spreading remains unchanged. However, many more tiles go corruptable, and will spread much faster. Read the table in the following way: Any of the spreading tiles can convert any of the pure tiles that are within a 7×7 foursquare centered on the converted tile (i.eastward. within iii blocks of the converted tile).^[ii]

Hardmode Spread Overview
Pure Tile	Converted Corrupt Tile	Converted Crimson Tile	Converted Hallowed Tile
Grass	Corrupt grass	Crimson grass	Hallowed grass
Rock Block	Ebonstone Block	Crimstone Cake	Pearlstone Cake
Mud Cake	Clay Block	Dirt Block	n/a
Ice Block	Purple Ice Block	Red Water ice Block	Pink Ice Block
Sand Block	Ebonsand Cake	Crimsand Block	Pearlsand Block
Hardened Sand Block	Hardened Ebonsand Block	Hardened Crimsand Block	Hardened Pearlsand Cake
Sandstone Block	Ebonsandstone Block	Crimsandstone Block	Pearlsandstone Block
Jungle grass	Decadent grass (converting the Mud Block underneath)	Cherry grass (converting the Mud Block underneath)	northward/a
Jungle thorny bushes	Corruption thorny bushes	Ruby-red thorny bushes	north/a

Defeating Plantera for the first time reduces the speed of the biomes' spread to fifty*1/two (l%) of the default Hardmode speed.

Grass [ ]

Similar regular grass, the evil and Hallowed variants spread as well. The mechanics described in this section do non change upon initiating Hardmode or defeating Plantera but instead remain the same for the entirety of the game.

For the purposes of grass spread, Abuse and Carmine thorny bushes are considered Corrupt/Crimson grass blocks, respectively.

The post-obit general restrictions utilize to all forms of grass spread, including pure grass:

Grass does non spread below the surface any. You demand to be at least at 4 feet (on the Depth Meter) on the surface for the grass under your anxiety being able to spread.
Grass only spreads to next tiles, i.eastward., tiles inside the viii tiles directly surrounding the spreading tile.
Grass does not spread to tiles that have lava in one of their adjacent tiles.
Grass only spreads to tiles that take at least 1 tile of open space within their side by side tiles.

All grass variants will spread to Dirt Blocks. Furthermore, evil and Hallowed grass blocks tin convert other grass as follows:

Spreading Grass Tile	Converts Grass
Spreading Grass Tile	Pure	Corrupt	Carmine	Hallowed
Corrupt grass	✔️	n/a	✔️	✔️
Crimson grass	✔️	✔️	n/a	✔️
Hallowed grass	✔️	✔️	✔️	n/a

All three grass variants spread in an equal way, hence there is none that is "faster" or "stronger", for example. Withal, Hallowed grass has the power to overtake Ruby-red grass.

In Hardmode, Corrupt, Crimson, and Hallowed grass will however grow to Dirt Blocks and infect other grass every bit described higher up. However, they additionally proceeds the ability to catechumen any corruptable tile within three tiles (just like the other spreading tiles) – including pure grass. Converting a tile that mode is handled differently and thus the restrictions outlined in a higher place do non employ. This allows them, for case, to infect pure grass below the surface, something which is not possible pre-Hardmode.

Evil and Hallowed grass will never catechumen any tile underneath a Sunflower. Note that while in pre-Hardmode, Sunflowers thus serve every bit an effective barrier, but spreading grass will be able to spread to tiles up to three tiles away in Hardmode, easily bypassing a single Sunflower.

Background Walls [ ]

For a technical explanation and the consummate algorithm in detail, come across the talk page.

Background walls cannot infect blocks, but they can be infected by blocks, and they can infect certain other walls within sure restrictions. Walls tin can also be converted past the initial Hardmode transition, or manually by the role player.

Natural or placed Grass Walls, Jungle Walls, and Flower Walls are all converted to infected Grass walls. Only pure walls are infected, and afterwards cannot be re-infected by a different biome.
Natural or placed Sandstone Walls or Hardened Sand Walls corrupt to the corresponding biome wall. Fifty-fifty if infected, these tin can be re-infected and converted to a dissimilar biome.
Stone walls cannot be infected this way, but Ebonstone and Crimstone walls can infect the other wall types listed above.
In all cases, any wall undergoing biome conversion (including from Thrown H2o or the Clentaminator) thereafter qualifies as a natural wall. This may impact enemy spawning, and perhaps the presence of the various Underground Desert biomes.

Pure Wall	Corruption	Red	Hallow
Grass Wall Flower Wall	Corrupt Grass Wall	Crimson Grass Wall	Hallowed Grass Wall
Jungle Wall	Corrupt Grass Wall	Crimson Grass Wall	due north/a
Rock Wall	Ebonstone Wall	Crimstone Wall	Pearlstone Wall
Hardened Sand Wall	Hardened Ebonsand Wall	Hardened Crimsand Wall	Hardened Pearlsand Wall
Sandstone Wall	Ebonsandstone Wall	Crimsandstone Wall	Pearlsandstone Wall

There are 2 overlapping patterns ("grassy" and "sandy") for infection of walls, depending on the contents of the source tile. Both patterns are considered for each tile update, and tin can separately infect different walls. The behavior tin can also vary according to whether the tile is above or below surface level, and which infection is being considered.

Common Rules [ ]

In all cases, wall infection range is 2 tiles (a five×5 square centered on the source tile), compared to 3 tiles for nigh blocks.
- As with blocks, Hallow cannot infect Jungle Walls
For a source tile to infect a wall, information technology must notice a qualifying foreground block or constitute with the infection in question (collectively, "biome blocks") either in the source tile, or within 20 tiles of information technology.
- The qualifying biome blocks vary with context, simply the following blocks always authorize: Grass, Water ice, Rock, Sand, and Vines.
- For Ruby, or to infect whatsoever grassy wall below surface level, the biome block must be in the source tile.
- Otherwise (infecting a grassy wall above surface level with Corruption or Hallow or any sandy wall), the biome block can be establish anywhere in a 20-tile range (a 41×41 foursquare centered on the source tile).

Grassy Wall Infection [ ]

If the source tile includes whatever natural infected Grass Wall, natural infected Stone Wall (except Pearlstone Wall) or infected grass cake, then it can attempt to infect a pure Grass, Flower, or Jungle Wall. Both natural and histrion-placed walls of these types can exist infected.

Each of the infectious biomes is checked in turn: Red, and so Corruption, then Hallow. If the tile has a qualifying wall and a grass tile from different biomes, it tin attempt to spread both biomes.
- For each infection attempt, a single tile within range is chosen, and if it is a pure grassy wall, it will be infected.
- Once more, infection needs a "biome block" as above:
  - For Crimson or if beneath surface level, then the biome block must be in the source tile, otherwise within 20 tiles.
  - In addition to the listing from higher up (Grass, Water ice, Stone, Sand, and Vines), Demonite Ore qualifies for Corruption. It only qualifies as a biome block in this step, and Crimtane Ore does not qualify for Crimson.
  - Most biome-specific plants (if infected) besides qualify as biome blocks here. This includes thorny bushes, tall grass/flowers (that is, growing from proper grass blocks), Vile/Vicious Mushrooms, and (once again) vines.
- As above, Hallow cannot infect Jungle Walls, and Pearlstone Walls cannot infect grassy walls at all.

Sandy Wall Infection [ ]

If the source tile contains any Sandstone Wall, any Hardened Sand Wall, and/or any Sandstone Cake, then it tin can endeavour to infect a Hardened Sand or Sandstone Wall.

Simply Hardened Sand or Sandstone Walls, pure or with whatsoever infection, are converted this fashion.
Unlike with grassy walls, simply ane biome is chosen, and then a single nearby tile is chosen for an infection attempt.
- To attempt infection, the source tile must have an infected wall and/or an infected biome block.
  - Qualifying walls include Grass, Stone, Sandstone, or Hardened Sand. (Note that the first ii imply a Sandstone Block from the offset step)
  - Qualifying biome blocks include the list from to a higher place (Grass, Water ice, Rock, Sand, and Vines), or Sandstone Blocks, but not other plants.
  - If the tile has different infections for wall and cake/vine, Crimson takes priority, then Hallow. Abuse applies only if at that place is no competing infection.

Notes [ ]

Spreading tiles can spread their biome even if there are not-corruptible blocks "in the way". For example, a one-block-broad wall of Wood between a Corrupt grass block and a pure grass block in Hardmode will not forbid the grass from being converted because the Corrupt grass tin can convert whatever tile within three tiles. Thus, to effectively stop the spread of a biome, at that place must be at least a 3-cake-wide obstacle of either open air or non-corruptible blocks.
The Crimson and the Hallow grow vines from beneath their respective grass blocks. These vines can spread their biomes to nearby blocks (in Hardmode) and walls as above. There are no Corrupt vines, and vines themselves cannot be converted except by converting the block they're connected to.
Stone Blocks with moss on them will be treated like regular Stone Blocks. The moss will exist destroyed upon conversion.
Thorny bushes abound from Corrupt and Ruby grass blocks, tin extend a significant altitude in any direction, and can furthermore spread the Corruption and Crimson, even over non-corruptible blocks. Therefore, it is possible for an evil biome to spread over a gap in pre-Hardmode, if its thorny bushes happen to grow beyond information technology and touch dirt or grass on the other side.
Chlorophyte Ore and Chlorophyte Bricks limit the spread of the evil biomes:
- If the Corruption attempts to convert either a Mud Block or a Jungle grass cake, or if at least one of the four tiles directly surrounding the target tile is a Mud or Jungle grass block, then it will cheque for the existence of nearby Chlorophyte: If at that place are at least v Chlorophyte tiles (regardless of whether Ore or Brick, both are added) within a radius of x tiles, the conversion will fail entirely. If there are fewer than 5, merely more than 0 Chlorophyte tiles, at that place is a chance of <tiles>/5 (eastward.g. three/5 if there are three Chlorophyte tiles) for the conversion to fail.^[3]
- The Red will always check for nearby Chlorophyte, regardless of the target or next blocks.
- Chlorophyte Ore can as well turn nearby dirt into mud, partly countering conversion impairment to the Jungle.
Considering the Hallow will not spread to mud or Jungle grass, creating artificial Hallow betwixt the Jungle and adjacent biomes tin also help to preserve the Jungle. For a more controlled solution, combine this with the above note and place Hallowed blocks directly side by side to small-scale Chlorophyte veins virtually the edges of the Underground Jungle.
- If the evil biome spreads virtually the vein past way of Jungle grass, and it is not large enough to outright cancel that spread, the Hallow will then begin spreading, and due to the slowing event of the Chlorophyte will quickly overtake the evil biome.
- If the evil biome does not spread near the vein, either by histrion action or due to it having grown large plenty to cease the spread, then the Hallow volition not spread at all.