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keithktam

how source port allow a 2.5d game look up and down

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Maes said:

Architectural degrees of freedom: As Gez said, Wolf3D's worlds are indeed purely 2D, as there's no way to set floor/ceiling height anywhere, and altitude plays absolutely no role in the engine. Now, imagine a Wolf3D map with different FLOOR heights only (the ceiling would be fixed). That would be 2.25D, I guess? Doom maps can be thought of as two such 2.25D maps "sandwiched" together (one for the ceiling, one for the floor)

Then ZDoom is 2.75D? Or 2.9D? Or what?

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Da Werecat said:

Then ZDoom is 2.75D? Or 2.9D? Or what?


Depends on how many RoR (or "ceiling-floor") layes you stack one on top of each other. The more you add, the more they will tend (asymptotically) towards 3D, and the more accurately you'll be able to represent an arbitrary 3D environment (at the cost of greatly complicated internal representation, though).

Each one should add half less depth than the previous, though, so that they never exceed 3D. 1/2 + 1/4 + 1/8 + 1/16 + ... ~= 1

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2.9D is a good fit for ZDoom. Internally it's managed as 3D as it can possibly get on the Doom architecture (meaning that while ZDoom does allow to stack unlimited numbers of 3D floors and actors can move above and below each others without problem, there's still the fact that the Z axis is a second-class citizen: Z-axis collisions are tested in a different and separate step from the X and Y axes collisions, and the underlying world representation, with its blockmap, BSP, and sectors, are still purely in 2D, with consequences on things such as "sound" propagation or lack of occlusion from 3D floors).

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speaking from a mathematic POV this makes no sense since 2.5D itself is already just a (not well defined) term for 3D graphics which don't use it to a full extent. this is not an actual number which counts the available space dimensions. saying the geometry has 2.5, 2.9 or 5.673 dimensions is equally nonsense. if they are limitations which doesn't allow specific geometric features it doesn't make it less 3D but just a subset of 3D and in this case still a true superset of 2D.

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^ That's why I made that DOF/DOC/map format differentiation before. You could say that Doom's map format is "2D plus a single pair of floor/ceiling information", if you want to avoid the "2.5D" terminology, which by itself, I agree, is ambiguous/meaningless.

Internally, the engine works primarily as 2D with extra checks for Z-axis collisions and drops, so you could say it's "2D plus some optional height-related checks, some of the time", but never is e.g. a full 3D euclidean xyz coordinate tuple used at any time in any distance, positioning etc. calculation. There's not even a terminal falling speed, or an artificially limited climbing speed for walking monsters (Doomguy and the monsters can climb incredibly fast and outpace flying monsters, if 1-px wide stairs are used).

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Maes said:

...
In any case, I thought that at this point, nobody would be offended if their favourite game was called "2.5D", "not really 3D" etc.: we're mature enough (?) to realize that what some called a weakness, was indeed Doom's strength...

I guess I'm still a baby - yeah, I take a bit of offense to "2.5D" - it's a bit of a sleight against the illusion being presented.

Sure, there's plenty of architexture you can't build, but what you can build is convincingly rendered in 3D (if the player is strapped in a wheelchair with a full neck brace on :) It's a limited view of true 3D. "2.5D" is lazy!

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