function virus_spread_viz()
    
    [X,Y,Z,Q] = get_earth_surface();
    %C = get_surf_color(Q);
    C = get_surf_color_random(Q);

    clf
    [xx,yy,zz] = get_curved_lines();
    hLine = zeros(size(xx,1),1);
    for i=1:numel(hLine)
        hLine(i) = line(xx(i,:),yy(i,:),zz(i,:), 'Color','m', ...
            'LineWidth',2, 'LineStyle','-');
    end

    hTxt = text(9,20,3.5, '', 'BackgroundColor',[.7 .9 .7]);

    hSurf = surface('XData',X, 'YData',Y, 'ZData',Z.*0.5, ...
        'CData',C);
    axis tight; grid on; box on; view(-15,30)
    zlim([0 6]); %axis([1 40 1 20 0 10])

    for i=1:100
        C = get_surf_color_random(Q);
        set(hSurf, 'CData',C)
        set(hLine(1), 'Visible',get_visibility())
        set(hLine(2), 'Color',rand(1,3))
        set(hLine(3), 'LineWidth',randi([1,5]))
        set(hTxt, 'String',get_string_random())
        drawnow
        pause(0.1)
    end
end

function [X,Y,Z,Q] = get_earth_surface()
    % lets create earth surface (X/Y/Z coords)
    [X,Y] = meshgrid(1:20,1:40);

    % continents
    Q = zeros(size(X));
    Q(20:35,3:7) = 1;   % north america
    Q(5:10,5:7) = 2;    % south america
    Q(7:17,10:14) = 3;  % africa
    Q(21:33,11:18) = 4; % europe
    Q(9:12,17:19) = 5;  % australia

    Z = zeros(size(X));
    Z(Q>0) = 1;
end

function C = get_surf_color_random(Q)
    sz = [40,20];
    C_r = zeros(sz);
    C_g = zeros(sz);
    C_b = ones(sz);
    for i=1:5
        C_r(Q==i) = rand();
        C_g(Q==i) = rand();
        C_b(Q==i) = rand();
    end
    C = cat(3, C_r,C_g,C_b);
end

function [x,y,z] = get_curved_lines()
    t = linspace(1,3,30);
    x = zeros(3,30);
    y = zeros(3,30);
    z = zeros(3,30);

    % [7,7,0]  -> [15,30,0]
    x(1,:) = spline(1:3, [7,11,15], t);
    y(1,:) = spline(1:3, [7,18.5,30], t);
    z(1,:) = spline(1:3, [0,2,0], t);
    % [5,30,0] -> [13,10,0]
    x(2,:) = spline(1:3, [5,9,13], t);
    y(2,:) = spline(1:3, [30,20,10], t);
    z(2,:) = spline(1:3, [0,3,0], t);
    % [18,10,0] -> [16,26,0]
    x(3,:) = spline(1:3, [18,17,16], t);
    y(3,:) = spline(1:3, [10,18,26], t);
    z(3,:) = spline(1:3, [0,2,0], t);
end

function str = get_string_random()
    alpha = 'a':'z';
    str = alpha(randperm(numel(alpha),randi([4 10])));
end

function vis = get_visibility()
    states = {'on','off'};
    vis = states{randi(numel(states))};
end