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##### 3.1.5.5 Transparency

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.