X Rendering Extension
xclock uses the render extension for rendering translucent and antialiased clock hands
|Original author(s)||X.Org Foundation|
|Stable release||0.11 / July 15, 2009|
The core X Window System drawing protocol does not have a way to efficiently draw transparent objects: A computer display is composed of individual pixels, which can only show a single color at a time. Thus transparency can only be achieved by mixing the colors of the transparent object to be drawn with the background color (alpha compositing). However, the standard X protocol only allows drawing with solid color, so the only way to achieve transparency is to fetch the background color from the screen, mix it with the object color, then write it back, which is fairly inefficient.
Since many operations require transparency (for example spatial anti-aliasing, especially during font rasterization, and transparency effects in window managers, such as transparent windows or menus), this limitation caused problems, and Xrender was implemented to address it.
It provides several rendering operations and also does alpha blending. As of 2011[update] it serves primarily to implement antialiased fonts, but for example KWin, KDE’s window manager uses it to draw drop shadows and translucency in case OpenGL is not available.
It is designed to target the 3D graphics capabilities of newer video cards.
Unlike OpenGL, it uses premultiplied alpha.
- "Design and Implementation of the X Rendering Extension". 2000. Retrieved 2013-11-03.
- Xft - the X Font library Drawing anti-aliased text with the core protocol involves fetching pixels from the destination, merging in the glyphs and shipping them back. This can be a performance problem when the latency between client and server is high.
- The X Rendering Extension (Keith Packard, Latest Official Specification)
- The Xrender Library
- A New Rendering Model for X (Keith Packard, USENIX 2000)
- High Performance X Servers in the Kdrive Architecture (Eric Anholt, USENIX '04)
- X.Org Glossary (X.Org)