Editing Invalid tile

An '''invalid tile''' is any tile that doesn't exist in, or any tile combination that is impossible in, the original Atari [[Lynx ruleset|Lynx]] version of [[Chip's Challenge]]. In Lynx, every square consists of an object (non-monster) and 0 or 1 [[monster]]s, including blocks and [[Chip]]. In [[MS Ruleset|MS]], a space is just something on top and something on bottom--even normal [[floor]] is actually a floor tile on a floor tile. MS also allows internal use tiles, like [[Burned Chip]] and [[Swimming Chip]], to be placed as if they are actual game elements. Any tile or tile combination that can be placed in MS but not Lynx is considered invalid.

[[Tile World]]'s Lynx generally does not allow play in levels with invalid tiles. Invalid tiles are present in [[Chip's Challenge Level Pack 2|CCLP2]] and many [[custom level set]]s, and a combination is distinguished in [[ChipEdit]] using the following:

[[File:ChipEditInvalid.png]]

== Single tiles ==

[[Fake exit]]s, [[Burned Chip]]s, [[Swimming Chip]]s, [[Drowned Chip]]s and the [[unused]] tiles were not seen as a tile themselves in [[Chip's Challenge 1|CC1]], and hence are not recognized by the original Lynx version. However, Tile World's Lynx mode allows the Swimming Chip to remain as is, turns the fake exit into a [[exit|real exit]] in Tile World versions prior to 1.3, and turns the four other tiles or all five into [[wall]]s depending on the version.

North and west [[thin wall]]s are never seen in CC1, and therefore are also not recognized by the original Lynx version. However, they are generally not considered invalid, and Tile World's Lynx allows them as is unless the program is run in pedantic mode.

== Transparency ==

Chip and monsters are both [[transparent]], meaning it was intended for other tiles to go underneath them. Every tile can be buried underneath monsters and Chip, with the exception of other monsters and another Chip. [[Key]]s and [[boot]]s are transparent, but ''cannot'' have any tiles buried underneath them, and it is unknown why these tiles were made transparent in the first place.

All non-transparent tiles, such as [[computer chip]]s, [[water]], [[lock]]s, and even [[floor]], will not allow tiles to be buried underneath them. The only exception is [[block]]s, which can conceal any tile but [[Chip]], [[monster]]s, [[clone block]]s, and another block.

== Preventing use of invalid tiles ==
Since invalid tiles make a level unplayable in Lynx, their use is discouraged. In [[ChipEdit]], hovering your mouse over any location will tell if the combination is invalid or not by showing '''**INVALID**''' in the top-right corner. There is also an option called ''Check'' which does not allow the placement of invalid tiles when designing a level. The latest version of CCEdit has a similar feature: it shows a small red triangle in the corner of a tile if it is invalid. The other two [[level editor|editors]] do not have this option, so the placement of invalid tiles is up to the discretion of the designer.

Fortunately, Tile World exports the locations of invalid tiles to a file called ''stderr.txt'', which allows the user to easily pinpoint the invalid tiles.

== Use in CCLPs ==
[[Thanks to...]] contains buried ice tiles at (0, 25), (5, 26), (10, 27), (19, 28) and (27, 29) meaning the Lynx version is unable to play the level. This is the first usage of invalid tiles in an official set, and is the only CC1 level to contain invalid tiles. CCLP2 incorporated invalid tiles into many different levels, but was the last community pack to do so. They were first seen in [[The Parallel Port]], and are present in 50 of the 149 levels. [[Chip's Challenge Level Pack 3|CCLP3]] is Lynx-compatible, and thus does not contain any invalid tiles. [[Chip's Challenge Level Pack 1|CCLP1]] and [[Chip's Challenge Level Pack 4|CCLP4]] do not use invalid tiles either, since they are also Lynx-compatible.
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