With this function you can set a circular region of a grid to a certain value. You need to supply a starting grid cell (as an x and y axis coordinate) as well as the radius of the disk to set and the value that you wish to set the disk too, as shown by the illustration below:
ds_grid_set_disk(index, xm, ym, r, val);
|val||The value to set with the cells within the disk.|
ds_grid_set_disk(grid, ds_grid_width(grid) div 2,
ds_grid_height(grid) div 2, 5, -4)
The above code will set a circular region with a radius of 5 cells in the ds_grid indexed in the variable "grid" to a value of -4.