Turbo Pascal 5.x and onwards were implemented using Turbo Vision, a really good, object-oriented UI framework [1]. Every view could render a sub-rectangle of itself on command into a buffer, which is how the UI was able to render drop shadows. The C++ version was open-sourced in 1997 and ported to a bunch of platforms including Linux [2].<p>[1] <a href="http:&#x2F;&#x2F;www.sigala.it&#x2F;sergio&#x2F;tvision&#x2F;html&#x2F;index.html" rel="nofollow">http:&#x2F;&#x2F;www.sigala.it&#x2F;sergio&#x2F;tvision&#x2F;html&#x2F;index.html</a><p>[2] <a href="http:&#x2F;&#x2F;tvision.sourceforge.net&#x2F;" rel="nofollow">http:&#x2F;&#x2F;tvision.sourceforge.net&#x2F;</a>