XRender1 was developed by Keith Packard around 2000. Keith solicited input from numerous players in the X windowing system community, including developers in the XFree86, QT, KDE, GTK, Gnome, and OpenGL projects.
The XRender extension replaced the pixel-based model of rendering graphics with an RGB-based model. The extension also implemented the compositing operations of Thomas Porter and Tom Duff2. This introduced transparency and a natural way to mix colors.
1. Keith Packard, Design and Implementation of the X Rendering Extension, http://keithp.com/~keithp/talks/usenix2001/.
2. Thomas Porter and Tom Duff. Compositing Digital Images. Computer Graphics 18(3):253-259, July 1984.