I am also surprised that a fixed file name is used. Why not calling, in
pseudocode, something in the vein of mkstemp(if $TMPDIR exists then
$TMPDIR+"/pngoutXXXXXX.png" else "/tmp/pngoutXXXXXX.png") or simply
mkstemp("pngoutXXXXXX.png")? It seems to me that mkstemp(…) and its sister
functions have more merits than a constant filename.
