[Plplot-general] peculiar "segmented" fills using shade plots / plplot 5.8.0 & 5.9.0

[David S. <dj...@ca...>]

Hello,

I am using plplot to produce some "shade" plots and have encountered  
some problems. I am running an out-of-the-box version of plplot 5.9.0  
installed via darwinports under Mac OS. I'm interacting with plplot  
via the C library bindings.

I would like to produce contour plots in which the contours are filled  
with a solid colour. Although the documentation implies that this is  
not possible, I gather from reading the examples that it is achieved  
by calling plpsty(0). Unfortunately, subsequent calls to plshades  
produce weirdly segmented images, in which the solid fill is broken up  
with unwanted lines, like this:

http://www.damtp.cam.ac.uk/user/djs61/figures.pdf

(This plot was produced by allowing plshades to consolidate  
rectangular fills - disabling this option produces an image formed by  
tiny areas of solid fill bordered by white lines. The plot comes from  
the pdfcairo device, but the same output is produced by any driver. By  
zooming in on the image, it's possible to see that the black lines  
which mark the contours are afflicted by a similar unwanted patterning  
with white lines.)

I have checked that the same effect is present if I compile the  
supplied examples which use plshades. To check that it's not just an  
issue with the version of plplot I have installed, I have checked that  
I get identical results running the out-of-the-box packaging of plplot  
available in Ubuntu, currently version 5.8.0.

Has anyone encountered this problem before, or could anyone suggest  
what might be the case?

Thanks very much in advance for your help,
Best wishes
David