zoom or scroll can fail to render all or part of plot line

[<pl...@pi...>]

HI,

In trying to pin down the previous issue, I managed to reproduce another 
bug that has been bugging me for some time that I was never able to pin 
down.

some times, when scrolling or zooming, parts or all of the plotted line 
fail to render (on wxt, not tested elsewhere)

gnuplot> f(x)=0

gnuplot> !cat "fx_test.dat"
-50 -0.8
0 0.8
50 -0.7


  plot "fx_test.dat" w l , f(x)


one scroll up looses the left leg of the plot line. Scolling back it 
returns and two or more events is fine. Just the one position is 
affected and is repeatable once it happens.

On starting again the same plan did not reproduce it so another factor 
also must be involved. I mention it anyway because this is a long 
standing  problem.

I similar zoom problem is that certain zoom selections can result in 
nothing getting plotted.

I usually have to fiddle around to find a similar zoom selection a bit 
larger that does render correctly.

I suspect these two defects have the same root cause.

regards, Peter.