function D = compute_levelset_shape(name, n, options)% compute_levelset_shape - compute some basic level set shapes%%   D = compute_levelset_shape(name, n, options);%%   name can be: 'circle', 'rectangle', 'small-disks', 'circlerect1',%   'circlerect2', 'square'.%%   Copyright (c) 2007 Gabriel Peyreoptions.null = 0;[Y,X] = meshgrid(1:n,1:n);switch lower(name)        case 'circle'        if isfield(options, 'center')            center = options.center;        else            center = [n n]/2;        end        if isfield(options, 'radius')            radius = options.radius;        else            radius = n/4;        end        D = sqrt( (X-center(1)).^2+(Y-center(2)).^2 ) - radius;    case 'rectangle'        if isfield(options, 'corner1')            c1 = options.corner1;        else            c1 = [0.2 0.2]*n;        end        if isfield(options, 'corner2')            c2 = options.corner2;        else            c2 = [0.8 0.8]*n;        end        D = max( max( c1(1)-X, X-c2(1) ), max( c1(2)-Y, Y-c2(2) ) );    case 'circlerect1'        if not(isfield(options, 'corner1'))            options.corner1 = [0.2 0.2]*n;        end        if not(isfield(options, 'corner2'))            options.corner2 = [0.8 0.8]*n;        end        options.center = options.corner2;        options.radius = (options.corner2(1)-options.corner1(1))/2;        D = max( -compute_levelset_shape('circle', n, options), ...                 compute_levelset_shape('rectangle', n, options));    case 'circlerect2'        if not(isfield(options, 'corner1'))            options.corner1 = [0.15 0.15]*n;        end        if not(isfield(options, 'corner2'))            options.corner2 = [0.65 0.65]*n;        end        options.center = options.corner2;        options.radius = (options.corner2(1)-options.corner1(1))/2;        D = min( compute_levelset_shape('circle', n, options), ...                 compute_levelset_shape('rectangle', n, options));    case 'square'        if isfield(options, 'width')            width = options.width;        else            width = 0.8*n;        end        if isfield(options, 'center')            center = options.center;        else            center = [1 1]*n/2;        end        options.corner1 = center(:)-repmat(width,2,1)/2;        options.corner2 = center(:)+repmat(width,2,1)/2;        D = compute_levelset_shape('rectangle', n, options);            case 'small-disks'        D = Inf*ones(n);        if isfield(options, 'nbdisks')            nbdisks = options.nbdisks;        else            nbdisks = 5;        end        x = linspace(0,n,nbdisks+1); x(end) = []; x = x+n/(2*nbdisks);        options.radius = 0.75*n/(2*nbdisks);        for i=1:nbdisks            for j=1:nbdisks                options.center = [x(i) x(j)];                D = min(D, compute_levelset_shape('circle', n, options) );            end        end    otherwise         error('Unknown shape.');end