[vJass] 2D Array

[~GaLs~]

Two dimensional arrays in vJass, since vJass is implemented on top of Jass, are just normal arrays in disguise, using a multiplication trick to convert 2-dimension indexes into a one-dimension one. The way to declare one of these arrays is: <type> array name[width][height], notice the real size of the array is width*height, this size suffers the same limitations as normal array's size, it cannot go above approximately 40800, and if this size is bigger than 8191, you will be using slower function calls instead of array lookups and multiple arrays in the final script, etc.

Declaration : <type> array name[width][height]

Let say, I have a 2D array var:

globals
    integer array int [10][10]
endglobals

And, I was told that the arrays are just normal arrays in disguise, using a multiplication trick to convert 2-dimension indexes into a one-dimension one.
And, the real size of the array is width*height.

So, int[1][2] = int[2][1]?

Since 1x2 = 2, and 2x1 = 2...

 

[Builder Bob]

int[1][2] != int[2][1]

int[1][2] => 1 + 2 * 10 = 21
int[2][1] => 2 + 1 * 10 = 12

int[x][y] => x + y * width

 

[~GaLs~]

Why x+y*width?
Isn't it just width*height?

 

[Darthfett]

Why x+y*width?
Isn't it just width*height?

X represents the column of the 2d array, Y represents the Row.

If our max width was "12" for example, array members would go:

[Y][X]:
[1][1], [1][2], [1][3], [1][4], [1][5], [1][6], [1][7], [1][8], [1][9], [1][10], [1][11], [1][12], [2][1], [2][2] ... etc.

This is creating a relationship between X and Y that is the same as that between an inch and a foot. 12 X's equal 1 Y, or 12 inches equal 1 foot. Since JASS is limited to just one array member, or just one form of measurement, we can use the formula:
index = x + y*width, OR
total inches = inches + feet * 12 to get the actual array index or inches. Because y always equals 12 X's, [4][1] will not equal [1][4].

If you just multiplied the two together, as you suggested above however, you'd get the same index.

 

[Tyrande_ma3x]

Wouldn't it start from [0][0] instead of [1][1]? Or 2d arrays aren't the same as a normal one?

 

[Darthfett]

Wouldn't it start from [0][0] instead of [1][1]? Or 2d arrays aren't the same as a normal one?

Yes, but I was just demonstrating.

 

[TriggerHappy]

http://clanmapz.com/forum/showthread.php?t=1503

^_^