XRender

XRender is an extension to the X Window System that provides advanced 2D rendering and compositing capabilities. Implemented as part of the X.Org server ecosystem, it forms the Render extension (often referred to simply as XRender) and exposes a structured pipeline for image composition, alpha blending, and transformed drawing.

At the core of XRender are Pictures, which represent image sources or destinations along with associated formats, transforms, and clipping information. A Picture can carry a 32-bit color with an alpha channel, enabling per-pixel transparency and smooth blending with other Pictures. The extension defines PictFormats and allows transformation and filtering of Pictures, including translation, scaling, rotation, and other affine operations. Compositing is driven by a set of operators (for example Over, Add, In, Out, Atop, Xor) that specify how a source Picture is combined with a destination Picture to produce a new result.

XRender supports solid fills, image compositing, and the use of patterns or sources with alpha to achieve translucent rendering. While not a full 3D API, it provides the foundational capabilities for anti-aliased text rendering, translucent UI elements, and complex 2D effects in X11 environments. It is commonly used by font rendering toolchains such as Xft and rendering backends like Cairo, which rely on XRender to accelerate 2D drawing on X11.

Historically, the Render extension was developed in the 1990s by Keith Packard and collaborators and became a standard part of X.Org servers. In modern desktop stacks and Wayland-based environments, XRender remains a reference path for 2D compositing in X11, though newer pipelines and compositors may operate outside of its scope.