Both PSTricks
and TikZ/PGF
support polygon options that
have the effect of making the polygon appear transparent. For
PSTricks
, keyword transpalpha
was used during initial
development of transparency features, and opacity
was adopted
later. Sketch
honors both. TikZ/PGF
uses opacity
only.
When transparent polygons are in the foreground, objects behind them
(drawn earlier) are visible with color subdued and tinted. The hidden
surface algorithm of sketch
works well with such transparent
polygons.
Note that cull=false must be used for rear-facing polygons to be visible when positioned behind other transparent surfaces.