How can a ButtonDownFcn in a patch or line handle detect which polygon or segment was clicked?

I want to detect user clicks on a polygon mesh I've drawn using patch(), and determine which polygon was clicked in. Although Matlab must have computed that information in order to detect the mouse click, I can't find it in the arguments passed to the ButtonDownFcn that I install into the patch handle. The arguments are a handle to the patch and a Hit structure that includes the IntersectionPoint but nothing else of much use.

In principle I can calculate which polygon contains that point, but I would just be repeating work that Matlab has presumably done already. Can I get it directly?

The same question applies to clicks on line objects.

Answer 1

[John D'Errico]

When I did this in the past (admittedly some years ago), I simply put that information into the callback I assigned to each object in the plot.

[Richard Kennaway]

The information about which polygon was clicked does not exist until the click happens. I can't use a separate patch for each polygon, because the overhead of creating thousands of handles is enormous.

[John D'Errico]

Yeah, I did not say it was trivial to do. In the case I had, I was indeed forced to plot each piece separately, with a callback that was unique to that object.

Answer 2

[matt dash]

I dont believe that Matlab has already calculated which face/edge/marker you clicked (I don't think hittest works that way). Assuming it's a 2D scene, for patches, you can use inpolygon (or http://www.mathworks.com/matlabcentral/fileexchange/27840-2d-polygon-interior-detection on the file exchange which may be faster).