Matlab Purple Rain

clear;

raindropsize = 200;
hf = figure(1);
loc = get(hf,'Position');
loc(3:4) = [600 400]; % make the figure 600x400
set(hf, 'MenuBar','none', ...
       'Position', loc, ...
       'Color', [0.1 0.1 0.1], ...
       'UserData', true, ...
       'ButtonDownFcn', @buttondownfcn_callback);
% have the axes take up the whole figure
ha = axes('Position',[0,0,1,1]);

% turn off axis tick marks and labeling
axis off;
% turn off automatic scaling of axis
axis manual;

% get random locations for rain drops
% row 1 is x values
% row 2 is y values
% row 3 is z values
dropLoc = rand(3,raindropsize);

% push the random y locations for each drop
% so that they are just off screen
dropLoc(2,:) = 1 + 0.2 * dropLoc(2,:);

% get speed and size based on z value
[dropsize, dropspeed, dropwidth] = rainDropCalc(dropLoc(3,:));

% init the raindrops
for k = 1:raindropsize
    lx = [ dropLoc(1,k) dropLoc(1,k)];
    ly = [ dropLoc(2,k)-dropsize(k) dropLoc(2,k)];
    % There is a vectorized version of the line fuction
    % but I hate to use this looped version so I can init
    % each rainDrop to its own LineWidth.
    hl = line(lx, ly, 'Color', [.9 .2 .9], 'LineWidth', dropwidth(k));
    set(hl,'UserData', dropspeed(k));
end

simulate = true;
while simulate
    hl = get(ha,'Children');
    N = length(hl);
    simulate = N > 0;
    resetRainDrop = get(hf,'UserData');
    for k = 1:N
        y = get(hl(k),'YData');
        dropspeed = get(hl(k),'UserData');
        y = y - dropspeed;
        if y(1) < 0
            if resetRainDrop
                % the raindrop fell off the screen
                % so reset it back to the top so it can fall again.
                y = 1 + 0.2 * rand;
                [newsize, newspeed, newwidth] = rainDropCalc(rand);
                y = [y+newsize y];
                set(hl(k), 'XData', rand*ones(1,2),...
                    'YData', y, 'Linewidth', newwidth, 'UserData', newspeed);
            else
                % just delete the raindrop
                delete(hl(k));
            end
        else
            % just move the raindrop
            set(hl(k),'YData',y);
        end
    end
    drawnow;
end
close(1);

function [dropsize, dropspeed, dropwidth] = rainDropCalc(z)

maxdropsize = 0.05;
maxdropspeed = 0.04;
maxdropwidth = 2.0;

% smaller z is closer, bigger, and faster
dropsize = maxdropsize * (1 - 0.9 * z);
dropspeed = maxdropspeed * (1 - 0.4 * z);
dropwidth = maxdropwidth * (1 - 0.9 * z);
end

function buttondownfcn_callback(src, ~)
% this allows us to end the simulation gracefully when the
% mouse button is pushed in the figure.
set(src,'UserData',false);
end