Ok. That is pointer to pointer!
png_bytep
= pointer to png_byte
If you eliminate png_bytep
and just use png_byte
your code will look like this.
int height = 10;
int width = 20;
png_byte **row_pointers;
row_pointers = (png_byte**)malloc(sizeof(png_byte*) * height); <-- This is basically your number of rows.. ie height of your matrix.
for(int y = 0; y < height; y++)
{
row_pointers[y] = (png_byte*)malloc(sizeof(png_byte)*width); <-- This is representing number of elements in each row.. so width.
}
Assuming your structure have two ints x and y. you must be filing data as below..
for(int i=0;i< height;i++)
{
for (int j=0;j<width;j++)
{
row_pointers[i][j].x = i*j;
row_pointers[i][j].y = i*j;
}
}
Assuming your map also have similar structure. This is how you copy data..
for(int i=0;i< height;i++)
{
for (int j=0;j<width;j++)
{
map[i][j].x = row_pointers[i][j].x;
map[i][j].y = row_pointers[i][j].y;
}
}