print ignores z order of stacked contours

Hi there,

suppose the following MWE:

A = peaks(10);
A(A<0) = nan;
contourf(A, 50, 'linecolor', 'none');
colormap(flipud(gray));

The problem now is, that one cannot distinct between the background of the contour and the surface of the contour since it is white on white. Hence, I want a frame around the surface but without the contour lines:

A = peaks(10);
A(A<0) = nan;
contourf(A, 'linewidth', 2);
colormap(flipud(gray));
hold on;
contourf(A, 'linecolor', 'none')
hold off;

This renders nice on screen with the expected result. When I now save the picture with

print(gcf, '-painters', '-r300', '-dpng', 'peaks.png');

or '-zbuffer' or '-opengl' (it doesn't make a difference), the contourf lines and the first contour show up on top:

Any idea how to fix that? As mentioned, I tried printing with '-zbuffer' and '-opengl' with no luck. I also tried to reorder using uistack, still with no luck. I'm stuck.

Sincerely

Florian

Answer 1

[Florian]

Solved it! The trick is to use the contour map, that is returned. Since I only want the outline of the surface, I first plot the contourf with 0 levels and take the contour map from that plot. Makes things a lot easier.

A = peaks(10);
A(A<=0) = nan;

% generate the outline
[C, ~] = contourf(A, 0, 'linewidth', 1);

% plot the contour
[~, h] = contourf(A, 50, 'linecolor', 'none');
colormap(flipud(gray));

% set background to red to make it transparent later
set(gca, 'color', 'red');

% fill off and on to apply the red background to holes
set(h, 'fill', 'off');
set(h, 'fill', 'on');

% obtain all lines of the outline
CC = C;
clear C;
n = 0;
sFrom = 2;
sTo   = 1;
while true
    n = n+1;
    sTo = sFrom+CC(2, sFrom-1)-1;
    C{n} = CC(:, sFrom:sTo);
    sFrom = sTo+2;
    if sTo == size(CC, 2)
        break;
    end % if
end % while

% now plot the outlines into the contour
hold on
for n = 1:numel(C)
    plot(C{n}(1,:), C{n}(2,:), 'k', 'linewidth', 2);
end % for
hold off

% save the figure
print(gcf, '-r300', '-dpng', 'peaks.png');

% use external tool mogrify to make everything in red transparent
system('mogrify -transparent red peaks.png');

This generates the desired result: