visualize_stream.m

% vector field
dxdt = @(x) [x(2);-x(1)];

% mesh
[GX,GY] = meshgrid(linspace(-2*pi,2*pi,100),linspace(-10,10,100));

% stream
DX = arrayfun(@(x,y) [1,0]*dxdt([x;y]),GX,GY);
DY = arrayfun(@(x,y) [0,1]*dxdt([x;y]),GX,GY);
[verts,averts] = streamslice(GX,GY,DX,DY,400);
iverts = interpstreamspeed(GX,GY,DX,DY,verts,1/60/3);

% visualize
v = VideoWriter('stream.m4v','MPEG-4');
v.FrameRate=60;
open(v)

nframe = 60*10-1;
seglen = 60;

offset =randi(seglen,numel(iverts),1)-1;
frames = cell(seglen,1);
for frame=1:seglen
    fig = figure(6);
    clf
    fig.Position = [fig.Position(1:2),1024,768];
    axes('Units', 'normalized', 'Position', [0 0 1 1])
    set(fig,'Color',[0,0,0.2])
    colormap([linspace(0,0,100);linspace(0,1,100);linspace(0.2,1,100)]')
    hold on
    for k=1:length(iverts)
        xy = iverts{k};
        C = mod((0:(size(xy,1)-1))-frame+offset(k),seglen)/(seglen-1);
        C = exp(-(1-C)*1);
        xy(end+1,:)=[0,NaN];
        patch(xy(:,1)',xy(:,2)',[C,0],'EdgeColor','interp','LineWidth',0.5)
    end
    xlim([min(GX(:)),max(GX(:))])
    ylim([min(GY(:)),max(GY(:))])
    set(gca,'Color',[0,0,0.2])
    drawnow
    frames{frame}=getframe(gcf);
end

for frame=1:nframe
    writeVideo(v,frames{mod(frame,seglen)+1})
end
close(v)