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  • Rolling fog

on 8 Nov 2023
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drawframe(1);
Write your drawframe function below
function drawframe(nn)
% Moon over rolling fog.
% Comments below,
% Persistent variables -> keep you from having to recompute these
% variables at each iteration / save computation time
persistent enz ags x d c mx my mn cmp
if nn == 1
% Everything is precomputed so we don't really need this -> undo to
% get different clouds each time
rng default
% Base vector for pixels
x = linspace(-1, 1, 240);
% Make complex 3D noise spectrum -> spectrally shaping using
% distance. This is expensive so only do once.
b=length(x);
d=x(1:2:end)/2;
c=length(d);
r = ifftshift(sqrt((x*2).^2 + d'.^2 + permute(x.^2, [1, 3, 2])));
ags = linspace(0, 2*pi, 49);
enz = exp(6i*randn(c, b, b))./max(r.^2.4,2e-5);
% Make moon
[mx, my] = meshgrid(x);
rd = (mx-0.6).^2 + (my+0.2).^2;
mn = 1 - erf(max(rd - 0.3, 0)*3);
% Custom colormap for clouds
cmp = linspace(0, 1, 256)'.*[1, 1, 1];
cmp(:, 1) = cmp(:, 1).^1.6;
cmp(:, 2) = cmp(:, 2).^1.6*0.97;
cmp(:, 3) = tanh(cmp(:, 3))*1.1;
end
% Compute current noise realization. Linear phase causes a looping
% shift and offset creates the cloud morphing.
dt = abs(ifftn(exp(1i*(x.*ags(nn)/2 - ags(nn)/2)).*enz));
% Tapering the noise
dt = 5*dt.*(d-d(1))'.*permute(erf((x - 0.1)*2)+1, [1, 3, 2]);
dt = dt(:, :, 1:end);
% Thresholding for transparency
ap = dt>0.08;
% Making it look like clouds / adding glint
c_alp = cumsum(ap, 3);
CLS = (1.1 - erf(c_alp/5)).*ap.*dt;
ALP = ap.*rescale(dt);
% Alpha blend across volume
[AI, AS] = P(ALP, CLS);
% Loop spatially / keeps formations in roughly same spot. Turn off to
% see a different cloud movement effect.
AI = circshift(squeeze(AI)', [0, -5*nn]);
AS = circshift(squeeze(AS)', [0, -5*nn]);
% Web Matlab's 3D rendering is so slow that this fails to execute if
% you use surf to blend the images, so let's use the alpha-blender used
% to flatten the clouds for the RGB background, moon and cloud layers
% Convert clouds to RGB image using custom colormap
C = round(min(AI*40, 1)*255+1);
C = double(ind2rgb(C, cmp));
% Permuter to work with alpha blending function convention
PP = @(x)permute(x, [3, 2, 1]);
% This is a mess, but, it computes the alpha then applies the alpha
% blender to each channel and combines to form an image.
A = PP(cat(3, AS, mn, ones(size(mn))));
IG = PP([P(A, PP(cat(3, C(:, :, 1), mn, 0*mn))); P(A, PP(cat(3, C(:, :, 2), mn, 0*mn))); P(A, PP(cat(3, C(:, :, 3), mn*0.9, 0*mn)))]);
% Now, show.
image(IG);
axis equal;
camva(5.8);
%S.D.G.
% Alphablend function
function [AIf, ASf] = P(ATf, CLSf)
ASf = ATf(1, :, :);
AIf = CLSf(1, :, :);
% Have alpha, have intensity, compress onto single plane using alpha
% blending formula
for nf = 2:size(ATf, 1)
APf = ASf;
ASf = APf + ATf(nf, :, :).*(1-APf);
AIf = (AIf.*APf + CLSf(nf, :, :).*ATf(nf, :, :).*(1-APf))./(eps + ASf);
end
end
end
Animation
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