Initial Submit.

Author: zappo2

parallax/README.md

@@ -0,0 +1,9 @@
+# Parallax Plot
+
+Code for displaying 2 images, one being visible, the other hidden, and revealed only by
+rotating the axes to a new view (parallax).
+
+- paralaxPlot.m  - Take two B&W images that are the same size and create the plot
+- dfltimg_parallax.m - Get images from the default image, and transform between 4 of them.
+
+![Default Images in Parallax](./parallax_demo.gif)

parallax/dfltimg_parallax.m

@@ -0,0 +1,62 @@
+function dfltimg_parallax()
+% Get the default image cdata and display 4 images in a rotating cube.
+
+    I = get(groot,'defaultimageCData');
+    defimage = pow2(I,47);
+
+    % Compute the images from the default CData
+    I1 = bitslice(defimage,42,46);
+    I2 = bitslice(defimage,37,41);
+    I3 = bitslice(defimage,47,51);
+    I4 = bitslice(defimage,5,8);
+
+    set(gca,'PositionConstraint','innerposition')
+
+    % Display a transition for each image in sequence.
+    parallaxPlot(I1,I2);
+
+    pause(1)
+    paratwist
+    
+    parallaxPlot(I2,I3);
+    
+    pause(1)
+    paratwist
+    
+    parallaxPlot(I3,I4);
+    
+    pause(1)
+    paratwist
+    
+    parallaxPlot(I4,I1);
+    
+    pause(1)
+    paratwist
+
+end
+function paratwist()
+% Rotate the axes to show off the paralax thing...
+
+    for idx=linspace(0,90,50)
+        view([ idx (cosd(idx*4)-1)*5 ]);
+        drawnow
+    end
+    
+end
+function b = bitslice(a,lowbit,highbit)
+    % BITSLICE(A,LOWBIT,HIGHBIT)
+    %
+    %   Scales return values so that the maximum is 1.0.
+
+    b = a / 2^(lowbit);
+    b = fix(b);
+    b = b / 2^(highbit - lowbit + 1);
+    b = b - fix(b);
+
+    b = b / max(b(:));
+
+    % To work with parallaxPlot, pull up only the brightest pixels.
+    b = floor(b*1.8);
+
+    b([end 1]) = 1;
+end

parallax/parallaxPlot.m

@@ -0,0 +1,107 @@
+function parallaxPlot(img1, img2)
+% PARAKKAXPLOT(IMG1, IMG2) - Plot scatter points that shows the black
+% and white IMG1 with IMG2 hidden behind IMG1 pixels.
+% Rotating the axes around Z will reveal IMG2, and hide IMG1 behind IMG2.
+
+    arguments
+        img1 (:,:) double
+        img2 (:,:) double
+    end
+    
+    [ verts1(:,2), verts1(:,1) ] = find(img1);
+    [ verts2(:,2), verts2(:,1) ] = find(img2);
+
+    verts3 = parallax(verts1, verts2);
+    
+    scatter3(verts3(:,1), verts3(:,3), verts3(:,2), 20, 'w', 'Marker','.');
+
+    view([ 0 0 ]);
+
+    axis vis3d padded on
+    box on
+    daspect([1 1 1]);
+    xticks([]);
+    yticks([]);
+    zticks([]);
+    set(gca,'ZDir','reverse',...
+            'Color','none',...
+            'BoxStyle','full',...
+            'XColor',[.5 .5 .5],...
+            'YColor',[.5 .5 .5],...
+            'ZColor',[.5 .5 .5]);
+    set(gcf,'Color','black');
+end
+
+function verts3 = parallax(v1, v2)
+% Convert img1 and img2 into a single set of vertices
+% which represent BOTH images, where 1 image is hidden behind
+% the other, but revealed with a view change.
+
+    verts3 = v1;
+    verts3(:,3) = -1; % Starts with img1, add Z values.  -1 means not used
+
+    % Basic idea:  V1 is the image we first show, this is the reference image.
+    % For each vertex in V2, find an unused vertrc in V1 at the same Y and set Z to the X.
+    % If NO MATCH, we need to add a new vertex
+
+    for idx = 1:height(v2)
+        % First find points that haven't been used yet.
+        match = find_matching_index(verts3, v2, idx, 'unused');
+
+        if match
+            % We have a match, set Z of a random pt in img1 to x of img2.
+            verts3(match,3) = v2(idx,1);
+        else
+            % We have no matches.  Look for existing matches of the Y coord, and hide
+            % our new point behind that.
+            match = find_matching_index(verts3, v2, idx, 'any');
+            if match
+                % We found at least one, so hide this new pixel behind one of them
+                verts3(end+1,:) = [ verts3(match,1) v2(idx,2) v2(idx,1) ]; %#ok
+            else
+                % No match - hide this in the margins
+                verts3(end+1,:) = [ -1 v2(idx,2) v2(idx,1) ]; %#ok                
+            end
+        end
+    end
+
+    % Lastly, find points from the first image (V1) that don't already
+    % have a corresponding point from the second image (V2), and move
+    % them behind other points in V2.
+    % Note: All points from V2 are now in our destination image VERTS3.
+    lost = find(verts3(:,3)==-1);
+    for lidx = 1:numel(lost)
+        idx = lost(lidx);
+        % Only find used points since we are finding homes for unused points.
+        match = find_matching_index(verts3, verts3, idx, 'used');
+        if match
+            verts3(idx,3) = verts3(match,3);
+        else
+            % Just ignore it.
+        end
+    end
+
+end
+
+function match = find_matching_index(dest, src, idx, flag)
+% For the DEST image, find a random vertex in DEST that matches the
+% SRC image point at IDX.
+% If UNUSED is true, make sure the found vertex has not be used already.
+    mask = dest(:,2)==src(idx,2);
+    switch flag
+      case 'unused'
+        % Only match vertices not yet used.
+        mask = mask & dest(:,3)==-1;
+      case 'used'
+        % Only match vertices that have been used.
+        mask = mask & dest(:,3)~=-1;
+    end
+    % Get the indices to the found points
+    match_indices = find(mask);
+    if isempty(match_indices)
+        match = 0;
+    else
+        % Of the found points, find a random vertex from that list.
+        match = match_indices(randi(numel(match_indices)));
+    end
+end