Controlling an Animation With Timeouts

Controlling an Animation With Timeouts

The program that performs an animation using timeouts is actually quite similar to the one using workprocs. The main difference is that the timeout interval has to be defined and functions that relied on the workproc now have to be defined to rely on the timeout. Note especially that redraw_proc() has to register a new timeout each time it's called.

You may find it most helpful to compare the full programs using xdiff or a similar tool. This section briefly points out the main differences between two example programs.

The redraw procedure is defined to have an additional argument, an interval ID.
work_animate: static Boolean redraw_proc(XtPointer clientData);
time_animate: static Boolean redraw_proc(XtPointer clientData,
XtIntervalId *id);
In time_animate, a timeout has to be defined; the example chooses 10 ms:
#define TIMEOUT 10 /*timeout in milliseconds*/
In the state structure, which defines the global UI variables, the interval ID instead of the workproc ID is included.
work_animate:
static struct { /* global UI variables; keep them together */
XtAppContext appctx;
Widget glxwidget;
Boolean direct;
XtWorkProcId animate_wpid;
} state;
time_animate:
static struct { /* global UI variables; keep them together */
XtAppContext appctx;
Widget glxwidget;
Boolean direct;
XtIntervalId animate_toid;
} state;
The menu() function and the map_change() function are defined to remove or register the timeout instead of the workproc. Here are the two menu() functions as an example:
work_animate:
static void
menu(Widget w, XtPointer clientData, XtPointer callData) {
int entry = (int) clientData;

switch (entry) {
case 0:
if (state.animate_wpid) {
XtRemoveWorkProc(state.animate_wpid);
state.animate_wpid = 0;
} else {
/* register work proc */
state.animate_wpid = XtAppAddWorkProc(state.appctx,
redraw_proc, &state.glxwidget);
}
break;
case 1:
exit(EXIT_SUCCESS);
break;
default:
break;
}
}
time_animate
static void
menu(Widget w, XtPointer clientData, XtPointer callData) {
int entry = (int) clientData;

switch (entry) {
case 0:
if (state.animate_toid) {
XtRemoveTimeOut(state.animate_toid);
state.animate_toid = 0;
} else {
/* register timeout */
state.animate_toid = XtAppAddTimeOut(state.appctx,
TIMEOUT, redraw_proc, &state.glxwidget);
}
break;
case 1:
exit(EXIT_SUCCESS);
break;
default:
break;
}
}
The redraw_proc() function has to register a new timeout each time it's called. Note that this differs from the workproc approach, where the application automatically continues animating as long as the system isn't doing something else.
static void
redraw_proc(XtPointer clientData, XtIntervalId *id) {
Widget *w = (Widget *)clientData;
draw_scene(*w);
/* register a new timeout */
state.animate_toid = XtAppAddTimeOut(state.appctx, TIMEOUT,
redraw_proc, &state.glxwidget);
}