Will O' Wisp

Eric Ludlam
/
Will O' Wisp

on 2 Dec 2023

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This entry implements a function to do primitive lighting on some patches. The wisp is a virtual light and the colors of the trees (patches) are modified based on the lighting algorithm. If I had used a real light object, they illuminate infinitely far from the source and would make the forest less spooky.

While there is a light object in here, I set it to black so it would have no effect on any patches. Instead, it triggers the patch object to compute vertex normals which is expensive (in characters) to do by hand.

function drawframe(f)
    E=4; % Size of the forest environment
    % Abbreviations
    J=@rand;
    K=@rescale;
    VN=@vecnorm;
    persistent L
    
    if f==1
        set(gcf,'color','k');
        
        % Select some nice tree locations
        %v1=[0 0 1.3
        %    1.4 0 1
        %    -1.3 0 1.2
        %    1 -1 1.3
        %    -1 -1 1.2
        %    -.5 -2.1 .9
        %    .34 -2 1
        %    .7 -2.3 .8
        %    -1.5 -4 1
        %    .6 1 1.2
        %    .4 2 1.3
        %    -.55 1.5 1.4];
        % Below is the compressed version of the above, saving almost 50 chars!
        v1=reshape(K('啥猸㦴檳䀘䪿岣摏㕱戭巫䦮啥啥啥䀘䀘⢩⫋⑧0檳耀留焗檳滵焗滵梑檳晰檳滵焗猸'-'0',-4,2),12,3);
        % Compressed version of color array: See parent of this remix
        B=(['ÆJJ';'ûÁ';'F.';'¶eU';'_ ';'¡g<';'¢aa';'·9'-' '])/256;
        G=([')';'B¬B';'pé';'ob';' ¡ ';'U~[';'JË«';'RîR']-' ')/256;
        for i=1:size(v1,1)
            %% Tree Trunks
            N=30;
            Q=.1;  % variation in distance from center
            RN=12;  % n pts in bounding rings
            rv=[.05 .02]; % Radius values
            rh=[0 1]; % Radius heights
                      % Random pts on cylinder
            rt=linspace(0,2*pi,RN+1);
            rt(end)=[];
            T=[J(1,N)*pi*2 rt rt];
            h=[K(randn(1,N)) ones(1,RN)*rh(1) ones(1,RN)*rh(2)];
            % Adjust the radius based on height
            R=interp1(rh,rv,h);
            pts=[cos(T).*R
                 sin(T).*R
                 h]';
            % triangulate the perfect cylinder
            tf=convhulln(pts);
            % Push points in/out with variance of Q
            D=(1-Q+J(1,size(pts,1))*(Q*2))';
            tv=pts.*(D.*[1 1 0]+[0 0 1]);        
            mkP(tf,(tv+v1(i,:).*[1 1 0]).*[1 1 v1(i,3)+.1],i,B,D);
            %% Tree tops
            N=150;
            % Alg for random distribution of pts on a sphere.
            T=J(1,N)*pi*2;
            u=J(1,N)*2-1;
            
            pts=[0 cos(T).*sqrt(1-u.^2)
                 0 sin(T).*sqrt(1-u.^2)
                 0 u ]';
            % triangulate the perfect sphere
            lf=convhulln(pts);
            % Push points around to make foliage frumphy
            Q=.15;
            D=(1-Q+J(1,size(pts,1))*(Q*2))';
            lvr=pts.*D;
            
            % Scale down into our world and push up into treetops
            ss=v1(i,3)*.34;
            llv=lvr.*[.12+ss .12+ss .08+ss]+[0 0 .1];
            mkP(lf,llv+v1(i,:),i,G,D);
            %% Bumpy high-res ground
            N=400;
            Q=.2;
            % coordinates
            T=J(1,N)*2;
            R=J(1,N)+.05;
            x=cospi(T).*R*E;
            y=sinpi(T).*R*E;
            % Triangulate the flat disc so we can draw it
            pv=[x' y'];
            pf=delaunay(pv);
            
            % Variation
            D=(J(1,size(pv,1))*Q)';
            % flip faces due to normals needing to match trees
            mkP(fliplr(pf),[pv D],4,G,D);
        end
        
        %% Our Wisp!
        L=line(1,1,1,'Marker','.','Markers',20,'Color','y');
        light('color','k'); % This light forces normals to be
                            % computed on the patches but since it
                            % is black, it has no visible effect.
            
        %% Decorate!
        set(gca,'position',[0 0 1 1],'vis','off','proj','p');
        axis([-E E -E E -1 E]);
        view(3);
        daspect([1 1 1]);
        campos([0 3 .5]);
        camva(60);
        camtarget([0 0 .7]);
        drawnow; % Force all vertex normals to be computed
    end
    
    %% Update Light
    lp=[cospi(f/24)*.5 sinpi(f/24)*1.5-.5 cospi(f/12)*.2+.7];
    set(L,'XData',lp(1),'YData',lp(2),'ZData',lp(3));
    %% Apply lighting to all the patches
    O=findobj('type','patch');
    for i=1:numel(O)
        doL(O(i));
    end
    function doL(p)
        % Perform a lighting operation on the object provided in p.
        % This algorithm is an adaption from the ML lighting
        % algorithm in webGL, but ignoring specular (to make it
        % spooky) and adding in distance based ambient lighting,
        % and adding range to the local light.
        cp=campos;
        v=p.Vertices;
        
        % Distance from camera, extending to range.
        gl_dist=K(min(VN(v-cp,2,2),max(E)),'InputMin',0,'InputMax',E*3);
        % Weight of ambient lighting.  Desaturate some of the red on tree in front
        w_amb=[.3 .4 .4].*(1.1-gl_dist);
        % Effects of the wisp
        s_diff=.7; % diffuse strength
        lr=1.5; % max distance light can illuminate
        d=v-lp;
        l_dist=min(VN(d,2,2),lr);
        s_dist=1-K(l_dist,'InputMax',lr,'InputMin',0);
        
        % Diffuse Weight
        % Invert vertex normals due to faces being in wrong order and - being short
        w_diff=L.Color.*dot(-p.VertexNormals,d./VN(d,2,2),2)*s_diff;
        
        % CbaseColorFactor (ambiant and diffuse)
        bcf = min(max(w_diff,0), 1).*s_dist;
        % Accumulate all the terms and put on patch as color
        set(p,'FaceVertexCData',min(p.UserData.*(w_amb+bcf), 1));
    end
    
    %% Shorten patch creation
    function mkP(f,v,i,C,D)
        % f - faces
        % v - vertices
        % i - thing index
        % C - Array of colors to pick from
        % D - distance array
        % Create our colors based on D
        bC=C(mod(i,size(C,1))+1,:);
        C2=hsv2rgb(rgb2hsv(bC).*[.1 1 .3]);
        q=bC-C2;
        fvc=K(D)*q+C2;
        % Create patch and stash colors
        patch('Faces',f,'vertices',v,'EdgeC','n','FaceC','i',...
              'Amb',1,'FaceL','g','FaceVertexC',fvc,'U',fvc);
    end
end