Rainy window

Adam Danz
/
Rainy window

on 19 Nov 2023

41
154
0
8
1998

drawframe(1);

Animated version of my 2022 minihack submission Rain On The Window Pane but this one has the following more-realistic raindrop properties:

Only the larger window raindrops fall down the window
When a window raindrop intersects with another drop, the larger drop absorbs the smaller drop
As the falling raindrops increase in size, they are stretched vertically and become narrower horizontally
As the falling raindrops increase in size, they fall faster

Did I capture that the raindrops are tickling down on glass or does this just look like rain falling (not on glass)? I can't tell but I sure did spend some time trying 😃 🌧️

function drawframe(f)
persistent T dropSzFcn dropFcn
if f==1 || isempty(T)
    rng(359,'twister')      % set the random number generator for reproducibility
    nc=50;                  % number of colors in colormap
    cmap=gray(nc);          % used to set the background color
    axes(Position=[0 0 1 1]) % example axes to full size of figure
    colormap(cmap(1:ceil(0.4*nc),:)) % cut out the upper (lighter) part of the colormap
    hold on
    % background image
    bx=1:50;              % set size of the square image
    by=exp(-(((bx-6).^2)/(2*8.^2))); % gaussian
    I=imagesc([0,1],[0,1],by'+0*bx); 
    axis tight equal off
    % add distant lights
    ncl=99;               % number of colors for the lights
    LC=hot(ncl);          % light colors
    nl=30;                % number of lights
    r=@()rand(nl,1);      % generate nlx1 random numbers 0:1
    b=bubblechart(r(),r(),r(),LC(randi(ncl,nl,1),:),MarkerEdgeColor='n'); % street lights
    figSz=get(gcf,'Pos');
    bubblesize([3,0.1*max(figSz(3:4))]) % Scale light size to figure size
    % blur the image
    % the background and lights are flattened into a single image and
    % blurred.
    f=getframe;
    b.delete
    I.CData=imfilter(flipud(f.cdata),ones(10)/100);
    % Add rain drops
    nd=99;                % number of drops
    T=table();            % use a table to store some variables
    T.obj=gobjects(nd,1); % droplet surf objects
    T.dropSz=nan(nd,1);   % scale factor for drop size
    dropSzFcn=@()max(min(randg(1),6),.8)/150;  % Drop size, truncated gamma distribution
    [x,y,z]=sphere(20);   % use a larger number for smoother raindrop surfaces, but slower.
    dropFcn=@(sz)surf(sz*x+rand,2*sz*y+rand*1.1,sz*max(z,0),... % function to create raindrops
        FaceCo='w',FaceAl=.2,EdgeCo='n',...
        SpecularSt=1,SpecularExp=2, ...
        DiffuseSt=1,AmbientSt=.1);
    for i=1:nd % Create the rain drops
        T.dropSz(i)=dropSzFcn();
        T.obj(i)=dropFcn(T.dropSz(i));
    end
    light(Po=[0.5 -1 0.1]); % rain drops should be dark on top and light on bottom
    xlim([0,1])
    ylim([0,1])
    set(gcf,Color='k')
end
% Add new drops
n=5;                     % number of rain drops to add
T2=table();              % create a temporary table to store variables
T2.obj=gobjects(n,1);    % droplet surf objects
T2.dropSz=nan(n,1);      % scale factor for drop size
for k=1:n                % add more raindrops
    T2.dropSz(k)=dropSzFcn();
    T2.obj(k)=dropFcn(T2.dropSz(k));
end
T=[T;T2];
% Determine which rain drops are falling by drop size (larger ones fall)
% figure(); histogram(T.dropSz)  % for decision making
T.isFalling=T.dropSz > 0.01; % Reduce threshold to increase the number of falling rain drops
% The amount of downward displacement is determined by drop size
for j=find(T.isFalling')
    T.obj(j).YData=T.obj(j).YData-T.dropSz(j); % shift downward
end
% Determine if any drops overlap
% Reduce the computational expense by assuming drops are rectangular and
% useing MATLAB's rectint, though it contains 1 extra step that isn't needed
% (computing area of overlap) but it's still fast and clean.
[mmy(:,1),mmy(:,2)]=arrayfun(@(h)bounds(h.YData,'all'),T.obj); % [min,max] for ydata
[mmx(:,1),mmx(:,2)]=arrayfun(@(h)bounds(h.XData,'all'),T.obj); % [min,max] for xdata
% Covert the drop's x and y data to rectangular vectors [x,y,width,height]
T.xywh=[mmx(:,1),mmy(:,1),diff(mmx,1,2),diff(mmy,1,2)];
% If a water drop is off the figure, remove it
T.isoff=mmy(:,2) < 0;
T.obj(T.isoff).delete;
T(T.isoff,:)=[];
% Compare all pairs of drops without duplicate comparisons
objPairs=nchoosek(1:height(T),2);
overlap=false(height(objPairs),1);
for q=1:height(objPairs)
    % Because we're treating the raindrops as rectangles, there will be
    % falsely labeled overlaps in the corner of the rectangles. To reduce
    % the number of false positives, we'll require the overlap to be at least
    % 21.5% of the smallest raindrop since a circle consumes 78.5% of its
    % bounding box.
    minArea=min(prod(T.xywh(objPairs(q,:),[3,4]),2))*(1-.785);
    overlap(q)=rectint(T.xywh(objPairs(q,1),:),T.xywh(objPairs(q,2),:)) > minArea;
    if overlap(q) && all(isvalid(T.obj(objPairs(q,:))))
        % highlight the overlapping raindrops, for troubleshooting
        % set(T.obj(objPairs(q,:)),'facecolor','m','AmbientStrength',1 )
        % Which drop has the smallest width?
        [~,minidx]=min(T.xywh(objPairs(q,:),3));
        % The smaller drop is absorbed (removed)
        T.obj(objPairs(q,minidx),:).delete;
        % Elongate the surviving droplet
        maxidx=abs(3*(minidx-1)-2);  % converts 2 to 1 or 1 to 2;
        yd=T.obj(objPairs(q,maxidx)).YData;
        ydmu=mean(yd,'all');
        ef=1.05;  % elongation factor
        T.obj(objPairs(q,maxidx)).YData=(ef*(yd-ydmu))+ydmu;
        % Update dropSz
        T.dropSz(objPairs(q,maxidx))=ef*T.dropSz(objPairs(q,maxidx));
        % Make the elongaged drops narrower
        xd=T.obj(objPairs(q,maxidx)).XData;
        xdmu=mean(xd,'all');
        T.obj(objPairs(q,maxidx)).XData=(1/ef*(xd-xdmu))+xdmu;
    end
end
% Remove rows of the table that belong to deleted rain drops
T(:,3:end)=[];  % Remove the columns that will be recomputed on next iteration
T(~isvalid(T.obj),:)=[];
end

Open in MATLAB Online

Animation

Remix Tree

Rainy window
Adam Danz