XCB

Encyclopedia : X : XC : XCB : XCB

In computing, XCB (X C Binding) is a C language binding for the X Window System. It aims to replace Xlib. The project was started in 2001 by Bart Massey.

Xlib/XCB provides application binary interface compatibility with both Xlib and XCB, providing an incremental porting path.

Contents

1 Aims of XCB
2 Example
3 References
4 External links

Aims of XCB

The main aims of XCB are:

reduction in library size and complexity;
direct access to the X11 protocol.

Secondary aims include making the C interface asynchronous, facilitating better multithreading and making extensions easier to implement (via XML protocol descriptions).

The core and extension protocol descriptions are in XML, with the C bindings created via XSLT. A tertiary aim is to repurpose these protocol descriptions for the creation of protocol documentation, further language bindings, and server-side stubs.

Massey has worked to prove XCB formally correct, using Z notation. (Xlib has long been known to contain errors.)

Example

/* Simple XCB application drawing a box in a window */

#include 
#include 
#include 


int main()
;


/* open connection with the server */
c = XCBConnect(NULL,NULL);
if (c == NULL) 
/* get the first screen */
s = XCBSetupRootsIter( XCBGetSetup(c) ).data;


/* create black graphics context */
g = XCBGCONTEXTNew(c);
w.window = s->root;
mask = XCBGCForeground | XCBGCGraphicsExposures;
values[0] = s->black_pixel;
values[1] = 0;
XCBCreateGC(c, g, w, mask, values);


/* create window */
w.window = XCBWINDOWNew(c);
mask = XCBCWBackPixel | XCBCWEventMask;
values[0] = s->white_pixel;
values[1] = XCBEventMaskExposure | XCBEventMaskKeyPress;
XCBCreateWindow(c, s->root_depth, w.window, s->root,
10, 10, 100, 100, 1,
XCBWindowClassInputOutput, s->root_visual,
mask, values);


/* map (show) the window */
XCBMapWindow(c, w.window);


XCBFlush(c);


/* event loop */
while (!done && (e = XCBWaitForEvent(c))) 
free(e);
}
/* close connection to server */
XCBDisconnect(c);


return 0;
}

XCB has a comparable, but slightly lower-level API than Xlib, as can be seen with this example.

References

[XCB: An X Protocol C Binding] (PDF) (Bart Massey and Jamey Sharp, 19 September 2001, presented at XFree86 Technical Conference 2001)
[XCL: An Xlib Compatibility Layer For XCB] (Jamey Sharp and Bart Massey, 15 April 2002, presented at USENIX 2002)
[X Meets Z: Verifying Correctness In The Presence Of POSIX Threads] (Bart Massey and Robert Bauer, 15 April 2002, presented at USENIX 2002)

External links

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