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 [SOLVED] Math problem with array .length  (Read 2383 times) 0 Members and 1 Guest are viewing this topic.
Yemto

Senior Devvie

Medals: 4
Exp: 3 years

 « Posted 2013-08-20 09:20:44 »

I believe this is quite simple. But I have never been good at math so I ask here before doing some thing dumb. In my game the world is build up in chunks, which is 32x32 tiles. The problem I have is moving a object to another chunk. It works as long as the coordinates are not negative. But if they are, it won't work. I have tried to do it on my own. But what that would require is an awful if statement to handles negative coordinates, and I think it could be done without an if statement

here is the code I have got working so far. I remove all attempts to do negative coordinates
 1  2  3  4  5 `int chunkX = getChunkX() + (x / Chunk.SIZE);int chunkY = getChunkY() + (y / Chunk.SIZE);        x = x%Chunk.SIZE;y = y%Chunk.SIZE;`

so what needs to happened. If a object is at 0,0 in chunk 5,5 and gets a order to move to 0,-1 the coordinates most change to 0,31 chunk 5,4

EDIT: I going to try to make it easier to understand.

I have big and small arrays set up like this.

The P is the player/Object. Now I want to move him to 3,-1 which would result in java.lang.ArrayIndexOutOfBoundsException So instead I want to move the Player/Object to 3x8 but in the big 0,-1 array. The problem is I don't know the math I need to do so I get the right big array, and the small array coordinates.

chunkX and chunkY is the big array x and y
x and y  is the small array x and y
Stranger
 « Reply #1 - Posted 2013-08-20 11:15:40 »

Anton
Yemto

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 « Reply #2 - Posted 2013-08-20 13:57:59 »

Riven

« JGO Overlord »

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 « Reply #3 - Posted 2013-08-20 14:01:43 »

To wrap on an axis (both positive and negative) do this:
 1 `x = (((x+n) % DIM) + DIM) % DIM`

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Yemto

Senior Devvie

Medals: 4
Exp: 3 years

 « Reply #4 - Posted 2013-08-20 20:07:43 »

To wrap on an axis (both positive and negative) do this:
 1 `x = (((x+n) % DIM) + DIM) % DIM`

Thank you so much. Me and some guys at work went nuts over this problem. It's finally fixed.

Here is the code I ended up using. Just to see if someone sees any issues.
 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20 `public void setTileFromWorld(Tile t, int x, int y){    int DIM = Chunk.SIZE;    int cx = (int)Math.floor(x / (double)DIM);    x = ((x % DIM) + DIM) % DIM;    int cy = (int)Math.floor(y / (double)DIM);    y = ((y % DIM) + DIM) % DIM;    for(Chunk c : chunks){        if(cx == c.getX() && cy == c.getY()){            c.setTile(t, x, y); return;        }    }    /*    System.err.println("An error occurred while trying to place a tile");    System.err.println("Chunk X: "+cx+" X: "+x);    System.err.println("Chunk Y: "+cy+" Y: "+y);    System.err.println(t);*/}`
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