Xlib â C Language X Interface

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Xlib − C LibraryX11, Release 6.7 DRAFT11.7. Getting Pointer Motion HistorySome X server implementations will maintain a more complete history of pointer motion than isreported by event notification. The pointer position at each pointer hardware interrupt may bestored in a buffer for later retrieval. This buffer is called the motion history buffer. For example,afew applications, such as paint programs, want to have a precise history of where the pointertraveled. However, this historical information is highly excessive for most applications.To determine the approximate maximum number of elements in the motion buffer, use XDisplay-MotionBufferSize.unsigned long XDisplayMotionBufferSize (display)Display *display;displaySpecifies the connection to the X server.The server may retain the recent history of the pointer motion and do so to a finer granularity thanis reported by MotionNotify events. The XGetMotionEvents function makes this history available.To get the motion history for a specified window and time, use XGetMotionEvents.XTimeCoord *XGetMotionEvents (display, w, start, stop, nevents_return)Display *display;Window w;Time start, stop;int *nevents_return;displaywstartstopSpecifies the connection to the X server.Specifies the window.Specify the time interval in which the events are returned from the motion historybuffer. You can pass a timestamp or CurrentTime.nevents_return Returns the number of events from the motion history buffer.The XGetMotionEvents function returns all events in the motion history buffer that fall betweenthe specified start and stop times, inclusive, and that have coordinates that lie within the specifiedwindow (including its borders) at its present placement. If the server does not support motion history,ifthe start time is later than the stop time, or if the start time is in the future, no events arereturned; XGetMotionEvents returns NULL. If the stop time is in the future, it is equivalent tospecifying CurrentTime. The return type for this function is a structure defined as follows:typedef struct {Time time;short x, y;}XTimeCoord;The time member is set to the time, in milliseconds. The x and y members are set to the241
Xlib − C LibraryX11, Release 6.7 DRAFTcoordinates of the pointer and are reported relative to the origin of the specified window. Tofreethe data returned from this call, use XFree.XGetMotionEvents can generate a BadWindow error.11.8. Handling Protocol ErrorsXlib provides functions that you can use to enable or disable synchronization and to use thedefault error handlers.11.8.1. Enabling or Disabling SynchronizationWhen debugging X applications, it often is very convenient to require Xlib to behave synchronouslyso that errors are reported as they occur. The following function lets you disable orenable synchronous behavior. Note that graphics may occur 30 or more times more slowly whensynchronization is enabled. On POSIX-conformant systems, there is also a global variable _Xdebugthat, if set to nonzero before starting a program under a debugger, will force synchronouslibrary behavior.After completing their work, all Xlib functions that generate protocol requests call what is knownas an after function. XSetAfterFunction sets which function is to be called.int (*XSetAfterFunction(display, procedure))()Display *display;int (*procedure)();displayprocedureSpecifies the connection to the X server.Specifies the procedure to be called.The specified procedure is called with only a display pointer. XSetAfterFunction returns theprevious after function.To enable or disable synchronization, use XSynchronize.int (*XSynchronize(display, onoff))()Display *display;Bool onoff;displayonoffSpecifies the connection to the X server.Specifies a Boolean value that indicates whether to enable or disable synchronization.The XSynchronize function returns the previous after function. If onoff is True, XSynchronizeturns on synchronous behavior. Ifonoff is False, XSynchronize turns off synchronous behavior.11.8.2. Using the Default Error HandlersThere are two default error handlers in Xlib: one to handle typically fatal conditions (for example,the connection to a display server dying because a machine crashed) and one to handle protocolerrors from the X server. These error handlers can be changed to user-supplied routines if youprefer your own error handling and can be changed as often as you like. If either function ispassed a NULL pointer, itwill reinvoke the default handler. The action of the default handlers isto print an explanatory message and exit.242
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AcknowledgmentsThe design and imple
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Release 6Stephen Gildea (X Consorti
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4.2. Translating Screen Coordinates
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10.7. Input Focus Events . . . . .
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13.5.6.1. Input Style . . . . . . .
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