This page provides information and resources about porting applications from Xlib to XCB. It discusses the Xlib Compatibility Layer, provides various examples, conglomerates past mailing list posts related to poring, and hopefully will become an important reference for developers who wish to utilize the power and simplicity of XCB by reprogramming their applications to it.

The Big Picture

The recommended way to port an application from Xlib to XCB is to begin by converting the internal interfaces and structures from Xlib types to XCB. For libraries, a two step strategy is recommended. First, begin by porting the public interfaces to use XCB types. Then, provide a thin wrapper library that provides the old interface, so legacy applications can use the newly ported library without any alterations. To help with this process, a small abstraction layer called the XCL is available.

The XCL

As mentioned elsewhere, the Xlib Compatibility Layer or XCL for short emulates Xlib but is built on XCB. This allows current applications built with Xlib to begin leveraging XCB's capabilities slowly over time; the entire program doesn't have to be ported immediately. Rather, it can continue to use various Xlib functions, data types, etc. while also using XCB's facilities, structures, and other resources simultaneously.

Before beginning to use the XCL, it is highly recommended that you read ?JameySharp and BartMassey's paper XCL: An Xlib Compatibility Layer for XCB. (There are also other formats and sources where this document can be found; see the Publications page.)

Using the XCL

To begin using the XCL just include the header file xcl.h rather than Xlib.h. After doing so, you will be able to a large majority of Xlib functions and types; XCB's functions, macros, data types, etc; and some convenient macros for converting Xlib types to XCB types.

Functions and Macros Available in xcl.h

The following functions provided by xcl.h can be used to cast from Xlib types to XCB types:

XCBConnectionOfDisplay, XCLATOM, ?XCLBUTTON, XCLCOLORMAP, ?XCLCURSOR, ?XCLDRAWABLE, ?XCLFONT, ?XCLFONTABLE, ?XCLGCONTEXT, ?XCLKEYCODE, ?XCLKEYSYM, ?XCLPIXMAP, ?XCLTIMESTAMP, ?XCLVISUALID, ?XCLWINDOW, ?XSetEventQueueOwner

Follow the function's link to see its prototype and an example of how to use it.

Past Posts

XNextEvent How to write the usual Xlib non-blocking event loop in XCB.

Examples

XcbPortingCreateCursor Creating a cursor from a standard font.

The Events section of the XCB Tutorial explains how to set up the event loop in XCB and compares the process with Xlib's XNextEvent and XPending.