(PECL ps >= 1.1.0)
ps_setdash — Sets appearance of a dashed line
$psdoc, float $on, float $off): boolSets the length of the black and white portions of a dashed line.
psdocResource identifier of the postscript file as returned by ps_new().
onThe length of the dash.
offThe length of the gap between dashes.
成功時(shí)返回 true， 或者在失敗時(shí)返回 false。