PBuffers

A pbuffer, short for pixel buffer, is an offscreen rendering surface used in OpenGL and related windowing systems. It provides a rendering target that exists in GPU memory but is not displayed on screen. Pbuffers were developed to enable rendering to an image or texture without requiring a visible window, facilitating tasks such as texture generation, image processing, or multi-pass rendering.

Pbuffers are created with window-system extensions (for example, GLX in X11 and WGL in Windows). They typically involve a separate OpenGL context that may share resources with the main context, allowing reuse of textures or buffers. A pbuffer can be configured with a specified color buffer and optional depth and stencil buffers, and it becomes the current draw surface when activated. After rendering, the resulting image can be used directly as a texture, or copied back to system memory or another buffer.

Common usage patterns include rendering a scene to a pbuffer and then transferring the result to a texture via a copy operation or by binding the texture and updating it from the pbuffer’s contents. Buffers can be read back with glReadPixels or used for subsequent processing in a separate rendering pass. Pbuffers were especially valuable before the widespread adoption of framebuffer objects, as they provided a portable offscreen target on systems lacking robust FBO support.

Today, pbuffers have largely been superseded by framebuffer objects (FBOs) in modern OpenGL, which offer more flexibility and simpler management. Nevertheless, pbuffers remain part of older codebases and certain platform-specific workflows where FBOs are not available or convenient.

See also: framebuffer object, GLX_pbuffer, WGL_pbuffer, ARB_pbuffer.