Question

I have a few values which are offsets to a multidimensional array , and look like this :

static const int TILE_SIZE = 32;
int Offset2D = (y * TILE_SIZE) + (x * TILE_SIZE);
int Offset3D = (y * TILE_SIZE) + (x * TILE_SIZE) + (z * TILE_SIZE);

Now what i would like to do is to convert an offset to x,y,z pair , like so :

void ConvertBack(int offset,int size,int& x,int& y,int& z)
{
    //What's wrong with this code ?
    x = offset / size;
    y = offset % size;
    z = ??; //How to get Z?
}

or

//Get back offsets from any dimension ?

void ConvertBackComplex(unsigned int offset,int size,int* vector,int len)
{
    for (int i = 0;i < len;i++)
    {
        vector[i] = offset ?... ?
    }
}

…So far all of my attempts have failed….So i would really welcome any help!…

Answer 1

First of all I think you indexing system is a bit off. The way you have things arranged different values of x, y, and z can give the same offset. So, first of all, assuming that TILE_SIZE is how many cells of the array store the data for a given point:

myArray = new arr[xSize*ySize*zSize*TILESIZE]
int offset2D = (x*ySize*zSize + y*zSize)*TILE_SIZE;
int offset3D = (x*ySize*zSize + y*zSize + z)*TILE_SIZE;

To get x,y,z back from the offset one simply does the following:

temp = offset/TILE_SIZE;
x = temp/(ySize*zSize);
y = (temp%(ySize*zSize))/zSize;
z = (temp%(ySize*zSize))%zSize;

For multiple dimensions:

temp = offset/TILE_SIZE;
sizeProduct = 1;
for(int k=1; k<numDims; ++k)
{
    sizeProduct*=size[k];
}
for(int i=0; i<numDims; ++i)
{
    vector[i]=temp/sizeProduct;
    temp = temp % sizeProduct;
    if((i+1)<numDims)
    {
        sizeProduct/=sizes[i+1];
    }
}

To calculate array sizes in multiple dimensions:

int arraySize = TILE_SIZE;
for(int i=0; i<numDims; ++i)
{
    arraySize*=sizes[i];
}

To calculate array indices in multiple dimensions (assuming vector is your array of coordinates):

int index =0;
sizeProduct = 1;
for(int k=1; k<numDims; ++k)
{
    sizeProduct*=size[k];
}
for(int i=0; i<numDims; ++i)
{
    index+=sizeProduct*vector[i];
    if((i+1)<numDims)
    {
        sizeProduct/=sizes[i+1];
    }
}
index*=TILE_SIZE;