# ds_grid_filter_gaussian_wrap

Performs a Gaussian convolution on a given grid, wrapping around the boundaries of the grid if needed.

Number keys select different values of sigma.Download
ds_grid_filter_gaussian_wrap(grid, sigma)
Performs a Gaussian convolution on a given grid, wrapping around the boundaries of the grid if needed.
COPY/// @func   ds_grid_filter_gaussian_wrap(grid, sigma)
///
/// @desc   Performs a Gaussian convolution on a given grid,
///         wrapping around the boundaries of the grid if needed.
///         If sigma <= 0, no operation is performed.
///
/// @param  {grid}      grid        grid data structure
/// @param  {real}      sigma       standard deviation
///

function ds_grid_filter_gaussian_wrap(grid, sigma)
{
if (sigma > 0)
{
//  Select suitable filter size for sigma
var size = ceil(6 * sigma);
var n = 2 * sqr(sigma);
var d = 1 / (sqrt(2*pi) * sigma);

//  Compute Gaussian coefficients
var g;
for (var i=size; i>=0; i--)
{
g[i] = exp(-sqr(i) / n) * d;
}

//  Create working grids
var w = ds_grid_width(grid);
var h = ds_grid_height(grid);

var sw = w + 2 * size;
var sh = h + 2 * size;

var work1 = ds_grid_create(sw, sh);
var work2 = ds_grid_create(sw, sh);
var grid2 = ds_grid_create(sw, sh);

//  Duplicate opposite edge data beyond bounds of input grid
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size-w, size-h);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size,   size-h);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size+w, size-h);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size-w, size);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size,   size);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size+w, size);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size-w, size+h);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size,   size+h);
ds_grid_set_grid_region(grid2, grid, 0, 0, w-1, h-1, size+w, size+h);

//  Filter horizontally
ds_grid_copy(work1, grid2);
ds_grid_multiply_region(work1, 0, 0, sw-1, sh-1, g[0]);
for (i=1; i<=size; i++)
{
ds_grid_copy(work2, grid2);
ds_grid_multiply_region(work2, 0, 0, sw-1, sh-1, g[i]);
ds_grid_add_grid_region(work1, work2, 0, 0, sw-1, sh-1,  i,0);
ds_grid_add_grid_region(work1, work2, 0, 0, sw-1, sh-1, -i,0);
}

//  Filter vertically
ds_grid_copy(grid2, work1);
ds_grid_multiply_region(grid2, 0, 0, sw-1, sh-1, g[0]);
for (i=1; i<=size; i++)
{
ds_grid_copy(work2, work1);
ds_grid_multiply_region(work2, 0, 0, sw-1, sh-1, g[i]);
ds_grid_add_grid_region(grid2, work2, 0, 0, sw-1, sh-1, 0,  i);
ds_grid_add_grid_region(grid2, work2, 0, 0, sw-1, sh-1, 0, -i);
}

//  Copy filtered data back to input grid
ds_grid_set_grid_region(grid, grid2, size, size, size+w-1, size+h-1, 0, 0);

//  Clean up
ds_grid_destroy(work1);
ds_grid_destroy(work2);
ds_grid_destroy(grid2);
}
}


Contributors: xot

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