将屏幕坐标转换为数组网格坐标

Question

I'm using ANSI C and looking to convert on-screen borland graphics coordinates ie (35,134) to a grid coordinate of (0,0). My grid creation function is as follows:

void createGrid(int ***a, int m, int n)
{
    int i,j,color=0;

    *a=(int**)malloc(sizeof(int)*n);    //reserves memory for n

    for(i=0;i<n;i++){   //external loop
        *(*a+i)=(int*)malloc(sizeof(int)*m);    //reserves memory for m
    if(a){
         for(j=0;j<m;j++){ //internal loop
            *(*(*a+i)+j)=color;
            }
        }
    }
}

As you can see, it is a dynamic grid and I have been unable to find the correct conversion method. All I've been able to find is a conversion method from array(0,1) to a single index. At this time, I'm working with a grid size of 30X30. My mouse follows on-screen coordinates and I need those coordinates to be converted to the grid position, so a color can be stored and read from such a position.

Answer 1

Well, after a lot of reading and exploring, I found the answer to this dilemma is taking the (coordinate-number of spaces after 0)/size of the cell. In the case of my previous formula, it's (52-32)/10=2. This formula works for both, x and y coordinates to convert them into i & j indexes for a two-dimensional array.