[fltk.general] filled non-convex polygon disappears when rotated

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filled non-convex polygon disappears when rotated Paul Hahn 00:38 Oct 24 top right image
 
I have a weird problem that seems specific to using fl_begin/end_polygon() with fl_vertex() to draw a non-convex polygon (i.e., a filled "+" marker). With zero degrees rotation, the polygon appears. But application of a rotation angle not a multiple of 90 degrees results in nothing visible.

In contrast, when using fl_begin/end_loop() with fl_vertex() to draw the outline for the same polygon, the polygon (boundary) appears reliably, no matter what the rotation angle.

When I repeat the experiment with other kinds of (convex) filled and rotated polygons, there are no problems.

This is the first time I have tried to use fl_begin/end_polygon(). I am motivated by the need to do rotations on the filled polygon. I figure I am doing something wrong but I do not know what. I have tried to double-check that I do not have some kind of problems with the vertices -- seems OK.

I have attached a file to demonstrate the problem. If anyone is patient enough to check into this and help, I would really appreciate it.

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