Make transparent contourf plot

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Lukas Bystricky
Lukas Bystricky on 24 Dec 2015
Commented: Walter Roberson on 19 Dec 2020
I'd like to overlay a contourf plot on top of a map of the world. To do this the contourf will need to be transparent. Following the instructions in Steve Lord's answer here I was able to get this to work on a Windows machine (I don't remember the Matlab version number, but it was not 2015). On my home Linux machine running Matlab 2015a, the code snippet from the above answer does not work. No error or warning message, it just does the contour plot and pauses at each step but the plot does not become more transparent.
Is there some issue with OpenGL in Linux that prevents this from working properly?
Edit: Here is the code snippet in question. This works on Windows, but apparently not on Linux.
z = peaks;
[c,h] = contourf(z); clabel(c,h), colorbar
% Set the figure Renderer to OpenGL, which supports transparency
set(gcf, 'Renderer', 'OpenGL');
% Find all the objects that are children of the contourgroup that have the FaceAlpha property
alphable = findobj(h, '-property', 'FaceAlpha');
for k = [1:-0.1:0.1 0.1:0.1:1]
% Change the FaceAlpha property, which will change the objects' transparency
set(alphable, 'FaceAlpha', k);
Lukas Bystricky
Lukas Bystricky on 25 Dec 2015
I did try that, but that gives the error message:
Error using opengl
Switching to software OpenGL rendering at runtime on unix is not supported.

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Answers (2)

Walter Roberson
Walter Roberson on 25 Dec 2015
R2014b and later generate contour objects that do not have a FaceAlpha property. As yet (R2015b) there is no documented way of controlling the transparency of filled contour objects.
Walter Roberson
Walter Roberson on 27 Dec 2015
Contours themselves never had an alpha: they happened to be implemented by something that could be broken apart to use an alpha, but it was not a feature of contours directly.
My understanding is that they are adding in functionality like this as they go. I do not have any information about when it will re-appear.

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Michael on 18 Dec 2020
One work around is to plot a surface and change the view. Here is an example
data = rand(100,100);
view([0 90])
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Walter Roberson
Walter Roberson on 19 Dec 2020
I think I remember seeing a way to get alpha in contours in more recent releases, but I would have to investigate further.

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