set-alpha in dc<%>

Determines the opacity of drawing, under certain conditions:

• pen- and brush-based drawing when get-smoothing produces 'smoothed or 'aligned, and when the drawing context is not an instance of post-script-dc%; and

• text drawing for most platforms (Mac OS X, X with Xft/fontconfig; transparency approximated under Windows by fading the drawing color), and when the drawing context is not an instance of post-script-dc%.

A value of 0.0 corresponds to completely transparent (i.e., invisible) drawing, and 1.0 corresponds to completely opaque drawing. For intermediate values, drawing is blended with the existing content of the drawing context.

• (send a-dc set-alpha opacity) -> void
     opacity : real number in [0, 1]