spurious lines in gs with antialiasing

[Petr M. <mi...@ph...>]

Well, it looks to me that it must be a bug in ghostscript -- some rounding 
of positions or whatever. Below is a simplest postscript code that 
demonstrates spurious lines in a pm3d-like image:

%!
/M {moveto} bind def
/L {lineto} bind def
/R {rmoveto} bind def
/V {rlineto} bind def
/C {closepath} def

% Change the position, and spurious lines may move!!!
-50 20 translate
1 1 translate

1 setlinewidth
0.5 setgray
/y {100} def
newpath 100 y M 100 0 V 0 100 V -100 0 V closepath fill
newpath 200 y M 100 0 V 0 100 V -100 0 V closepath fill
newpath 300 y M 100 0 V 0 100 V -100 0 V closepath fill
newpath 400 y M 100 0 V 0 100 V -100 0 V closepath fill
newpath 500 y M 100 0 V 0 100 V -100 0 V closepath fill

/y {300} def
newpath 100 y M 100 0 V 0 100 V -100 0 V 0 -100 V closepath fill
newpath 200 y M 100 0 V 0 100 V -100 0 V 0 -100 V closepath fill
newpath 300 y M 100 0 V 0 100 V -100 0 V 0 -100 V closepath fill
newpath 400 y M 100 0 V 0 100 V -100 0 V 0 -100 V closepath fill
newpath 500 y M 100 0 V 0 100 V -100 0 V 0 -100 V closepath fill

showpage


You can change the resolution "-r50" and see how the spurious lines are 
moving.

a=demo2.ps

A="-dGraphicsAlphaBits=4"

D=png16m
#D=png256

gs -q -r50 $A -sDEVICE=$D \
         -dSAFER -dNOPAUSE -dBATCH -sOutputFile=$a.png $a -quit
gqview $a.png


Questions to postscript gurus:
1. Is it a gs bug?
2. Can gnuplot overcome it? (Ignore antialiasing, ...)

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PM