Adding Drop Shadows with PHP - Setting the Shadow Options
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Various factors can influence the appearance of the drop shadow. Some of these options can be defined as a set of constants at the beginning of our script to make our script more flexible. Changing them would affect the look of the drop shadow with little work in the future.
The DS_OFFSET constant represents the drop shadow's offset and will be used as the shadow's displacement distance from the top left corner from that of the original image. The DS_STEPS constant is the number of steps (or how many colors) that will be used when drawing the shadow to fade from black to the background color. The DS_SPREAD constant is the shadow's spread and affects how far one step should be from another.
I've assigned them values I personally find reasonable; your situation or preferences may vary.