[Plplot-devel] [RFC] Patch inplement plarc clipping

[Mark de W. <m.d...@da...>]

Hi,

In our application we draw a graph using an extcairo device. While 
testing on a 32 bit system I ran in an issue. When zooming in on a graph 
the cairo context got the status CAIRO_STATUS_INVALID_MATRIX. 
Reproducing the issue pointed to the function plP_wcpcx. The function 
returned a PLINT_MIN due to a the double result being too large. (It is 
implementation defined whether C returns the largest or the smallest 
value in this case.) This caused an 'a' of 0, which was where cairo got 
its CAIRO_STATUS_INVALID_MATRIX status. This issue was caused by circles 
drawn outside the clipping area of the plot.

The issue occurs both with plplot 5.10.0 as shipped with Debian Strech 
and the current git master.

I created a small patch which seems to fix the issue for me. It simply 
does not draw the arcs that are fully outside the clipping area. I'm not 
entirely sure whether this is the right solution, but it fixes the issue 
for me. The patch contains a debug printf for testing purposes. I 
modified example 3 to reproduce the issue. The x value becomes PLINT_MIN 
on a 32 bit system. The output of x03 on the console with the plarc 
patch applied is:
xscl[0] 2144687274, xscl[1] 2145210464
xscl[0] -2147483648, xscl[1] -2147483648

Is this patch the right approach?

Regards,
Mark de Wever