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[nikki]

Hello,

i am trying to implement a tile transition.
i've found this handy article http://www.gamedev.net/reference/articles/article934.asp

the thing i don't fully grasp is the bitwise technique they use.
i believe checking each cell in a complicated if, elseif way for 32 different posibilities is not exactly the way to go, and thats why i suspect the usage of bitwise things, but i don't get it, 

Has anybody here had some experience in a technique like this ?, and could you explain the neighbour checking ?

[st33d]

Personally I'd do it the if/else way and just pre-cache the result.

Accounting for every possible transition between tiles is going to enter massive if/else territory whether you like it or not. Perhaps the better solution would be to reduce the number of possible transitions.

[Sam]

edit An expanded version of this post is available at my site here. /edit

The bitwise technique basically does the same as a huge if/else statement, but saves on typing.

Much easier to first think of it first for a map with just two types of terrain - let's say rock and open air.

A simple map might look like this, with the filled tiles being where there's rock:



The key to the bitwise method is to assign a value to each tile depending on its neighbours.  For this example let's use the following values:



We visit each tile that is meant to be filled with rock, and examine its immediate neighbours to come up with a number for that tile.  If the tile directly above this one is also filled then the number is 1.  If the tile directly above AND the tile directly below is filled, then the number is 1 + 4 = 5.

Here's that tile map filled out with the correct numbers.



The clever bit is we can now directly convert those numbers into graphical tiles, so skipping having to write a huge if/else statement.  Here is a tileset, laid out in the order matching the valuing system we picked:



See how each tile graphic matches what would be expected of its corresponding number?

Now our game can just look at the number calculated for each filled tile, and pick out the correct tile to place there:



It would be the same principle even if you want to consider diagonal neighbours, or more varied types of terrain.  You'll just end up with a larger range of numbers.

The reason it's referred to as bitwise is because the values we're assigning to neighbouring tiles follows the same 2^n pattern as binary numbers.

[Ivan]

I nominate this to be the most helpful thread response ever.

[Aquin]

Yeah, this is pretty damn handy.  Bookmarked! 

[AdamAtomic]

thank you for the wisdom and clarity of thought   very cool!

[nikki]

While you were making that GREAT little tutorial, i went deep in the google power and learned by myself,
when i figured the binary business and the careful laying out of your tilemap out.

it is a brilliant technique , instead of writing endless if elseif (and nested aswell) mumbo jumbo , i only need 4 or 8 if statements , you add the outcomes and voila your tilenumber !

It felt so great i started drinking beer, and now hav written an scrambled post 

[AdamAtomic]

Ok rolled this into flixel.  I also built an alternate 12-tile variant that doesn't handle 1-tile wide or 1-tile tall solid areas, but DOES do interior corners.  Is handy if you're doing zelda or RL instead of cavestory or mario

[gimymblert]

The greatest most effective short tile tutorial i have ever read...
It solve one of my concern with 3D tile and i also figured that i could use bit on diagonal to distinguish between a turn and a solid corner...

In fact i works with any isotropic shape tile system, as long as yout correctly tag bitwise neighbor cell 

Officially awesome

[shrimp]

Good stuff! Also, Gyorgy Straub used this for some tiles for Assemblee - here

[increpare]

Oh, I never thought of doing it that way before.  Nice : D

[Laremere]

That is an amazing technique, thanks a ton.

[Parthon]

I used this same technique in Sim Cavern and it works really well. I ended up with a 4bit, 16 tile internal wall system that was very easy to work with, as well as nice and dynamic.

I'm working on a corner based 4bit x 4 system. It would require 64 x 1/4 size tiles to draw though, which may be a bit much. It would mesh a bit better though.

[deadeye]

This is ace, thank you Salt

[pgil]

Wow, this is so simple. I got it working in Game Maker in about 2 minutes. Thanks, Salt 

[gambrinous]

ooo this is a nice explanation, bookmarking!

[Eendhoorn]

Bit of an old topic, but this deserves some attention :D
I was looking at this thinking this is one of those things that sound like it should work easily, but require alot of tweaking. But I worked on this for about 2 hours yesterday and it works perfectly.

However, there seem to be some situations where you can't solely depend on this technique:


Both are grass transitions, but they need to respond differently according to their surrounding tiles. There is no way to work around this then by using if statements right?

I could sort of see this working with different values for the surrounding tiles, water having higher numbers values than sand for example. But I am nowhere near genious enough to come up with an elegant solution for that 

[Henry141]

Well, omgnoseat, this can easily be expanded to supporting that.

Just have the standard 1 2 4 8 for the four water tiles around the grass tile, but then carry on the progression for the four sand tiles, so they would be 16 32 64 128. This should still generate a completely unique number, this time between 0 and 240, and so you should be able to support 8 different textures in a standard 32 bit integer,  and there are probably other workarounds too.

[Fallsburg]

This article does a good job at looking at all of the different types of connections that you would want from a binary tilemap.

To get perfect inner and outer corners, you need 47 tiles (unless you don't care about inner tile [15 in Sam's example]).

[Eendhoorn]

Thanks for the replies guys, was exactly what I was looking for!

This article does a good job at looking at all of the different types of connections that you would want from a binary tilemap.

To get perfect inner and outer corners, you need 47 tiles (unless you don't care about inner tile [15 in Sam's example]).

I'm currently looking into "the blob" method which is mentioned in the article, but bitwise operations are not mentioned
Which values would the 4 corner tiles need to implement this method?

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