imagesetstyle() sets the style to be used by all
line drawing functions (such as imageline()
and imagepolygon()) when drawing with the special
color IMG_COLOR_STYLED or lines of images with color
IMG_COLOR_STYLEDBRUSHED. Returns TRUE on success or FALSE on failure.
The style parameter is an array of pixels.
Following example script draws a dashed line from upper left to
lower right corner of the canvas: