X Window Programming/XCB
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[edit] Introduction
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.
[edit] 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.)
[edit] Example
/* Simple XCB application drawing a box in a window */ #include <X11/XCB/xcb.h> #include <stdio.h> #include <stdlib.h> int main() { XCBConnection *c; XCBSCREEN *s; XCBDRAWABLE w; XCBGCONTEXT g; XCBGenericEvent *e; CARD32 mask; CARD32 values[2]; int done = 0; XCBRECTANGLE r = { 20, 20, 60, 60 }; /* open connection with the server */ c = XCBConnect(NULL,NULL); if (c == NULL) { printf("Cannot open display\n"); exit(1); } /* 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))) { switch (e->response_type & ~0x80) { case XCBExpose: /* draw or redraw the window */ XCBPolyFillRectangle(c, w, g, 1, &r); XCBFlush(c); break; case XCBKeyPress: /* exit on key press */ done = 1; break; } 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.
[edit] References
- XCB: An X Protocol C Binding (
) (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)
