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Parallel Universe: Difference between revisions
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[[File:ParallelUniverseViews.jpg|thumb|A diagram of Parallel Universe movement in [[Hazy Maze Cave]], after [[Mario]] has returned to the main map.]] | [[File:ParallelUniverseViews.jpg|thumb|A diagram of Parallel Universe movement in [[Hazy Maze Cave]], after [[Mario]] has returned to the main map.]] | ||
A '''Parallel Universe''', or '''PU''', is a region of space located far outside the intended map boundaries that reflects certain aspects, | A '''Parallel Universe''', or '''PU''', is a region of space located far outside the intended map boundaries that reflects certain aspects, notably the floors and ceilings, of the main map. | ||
== Explanation == | |||
When the game looks for floors below (or ceilings above) a given object (including Mario), it first "truncates" the object's position from a floating point value to a 16-bit integer value. The range of a floating point value is much larger, by a factor of roughly 10<sup>34</sup>, than the range of a 16-bit integer value, which ranges from -32,768 to 32,767 (-2<sup>15</sup> to 2<sup>15</sup> - 1). If a coordinate of the object's position falls outside the range of a 16-bit integer, it "wraps around" due to the binary bits outside the 16-bit range getting truncated. For example, if one of these floating point values is 40,000, then 40,000 - 65,536 = -25,536 will be used when determining if the object is aligned with a floor or ceiling. This gives the illusion that the floors and ceilings of the main level map are "copied" repeatedly in a uniform 3D grid, at a spacing of 65,536 units. | |||
[[File:Visible PU.png|thumb|184x184px|Frame of Peter Fedak's video where he turns Parallel Universes visible using hacks; notice the lack of [[objects]]|right]] | [[File:Visible PU.png|thumb|184x184px|Frame of Peter Fedak's video where he turns Parallel Universes visible using hacks; notice the lack of [[objects]]|right]] | ||
The truncation responsible for the existence of parallel universes is only performed when determining alignment with floors and ceilings. This means that walls and objects, both of which use floating point arithmetic to determine collision, do not "exist" in PUs, unless they are brought there. | The truncation responsible for the existence of parallel universes is only performed when determining alignment with floors and ceilings. This means that walls and objects, both of which use floating point arithmetic to determine collision, do not "exist" in PUs, unless they are brought there. | ||