(PECL ps >= 1.1.0)
ps_setgray — Sets gray value
$psdoc
$gray
Sets the gray value for all following drawing operations.
psdoc
Resource identifier of the postscript file as returned by ps_new().
gray
The value must be between 0 (white) and 1 (black).
成功时返回 true， 或者在失败时返回 false。
true
false
