Custom Event Loop

From Agar

The flow of instructions in a GUI application is typically such that, after some initialization steps, a body of code called the event loop (or main loop) is executed repeatedly, until the application terminates.

Agar provides one trivial event loop routine (AG_EventLoop()), which is suitable to most ordinary applications. It periodically updates the display, processes incoming events, and updates active timers.

Example code

The following code is taken from demos/customeventloop. The basic requirements for an event loop are:

Call AG_BeginRendering() to prepare for rendering of GUI elements.
Invoke AG_WindowDraw() to render visible windows (under framebuffer modes, video regions are not updated immediately.)
Call AG_EndRendering() (under framebuffer modes, the video updates happen here.)
Look for events with AG_PendingEvents(), retrieve them with AG_GetNextEvent(), and possibly process them with AG_ProcessEvent().
Update its wheel of time by calling AG_ProcessTimeout(). As an optimization, you only need to call the function if the macro AG_TIMEOUTS_QUEUED() evaluates to 1.

/*
 * This application demonstrates the use of a custom event loop.
 */
 
#include <agar/core.h>
#include <agar/gui.h>
 
int pressedKey = 0;			/* Last pressed key */
int xClick = 0, yClick = 0;		/* Last clicked x,y */
int curFPS = 0;				/* Measured frame rate */
const int nominalFPS = 1000/30;		/* Nominal frame rate */
 
/*
 * Our custom event loop routine. 
 */
static void
MyEventLoop(void)
{
	AG_Driver *drv;
	AG_Window *win;
	Uint32 t1, t2;
	AG_DriverEvent dev;
 
	t1 = AG_GetTicks();
	for (;;) {
		t2 = AG_GetTicks();
 
		if (t2-t1 >= nominalFPS) {
			/*
			 * Case 1: Update the video display.
			 */
			AG_LockVFS(&agDrivers);
 
			/* Render the Agar windows */
			if (agDriverSw) {
				/* With single-window drivers (e.g., sdlfb). */
				AG_BeginRendering(agDriverSw);
				AG_FOREACH_WINDOW(win, agDriverSw) {
					AG_ObjectLock(win);
					AG_WindowDraw(win);
					AG_ObjectUnlock(win);
				}
				AG_EndRendering(agDriverSw);
			} else {
				/* With multiple-window drivers (e.g., glx). */
				AGOBJECT_FOREACH_CHILD(drv, &agDrivers,
				    ag_driver) {
					if (!AGDRIVER_MULTIPLE(drv)) {
						continue;
					}
					win = AGDRIVER_MW(drv)->win;
					if (win->visible) {
						AG_BeginRendering(drv);
						AG_ObjectLock(win);
						AG_WindowDraw(win);
						AG_ObjectUnlock(win);
						AG_EndRendering(drv);
					}
				}
			}
			AG_UnlockVFS(&agDrivers);
 
			t1 = AG_GetTicks();
			curFPS = nominalFPS - (t1-t2);
			if (curFPS < 1) { curFPS = 1; }
 
		} else if (AG_PendingEvents(NULL) > 0) {
			/*
			 * Case 2: There are events waiting to be processed.
			 */
			do {
				/* Retrieve the next queued event. */
				if (AG_GetNextEvent(NULL, &dev) == 1) {
					switch (dev.type) {
					case AG_DRIVER_MOUSE_BUTTON_DOWN:
						xClick = dev.data.button.x;
						yClick = dev.data.button.y;
						printf("Click at %d,%d!\n",
						    dev.data.button.x,
						    dev.data.button.y);
						break;
					case AG_DRIVER_KEY_DOWN:
						pressedKey = (int)dev.data.key.ks;
						printf("Key down: %d (0x%x)\n",
						    (int)dev.data.key.ks,
						    (Uint)dev.data.key.ucs);
						break;
					default:
						break;
					}
 
					/* Forward the event to Agar. */
					if (AG_ProcessEvent(NULL, &dev) == -1)
						return;
				}
			} while (AG_PendingEvents(NULL) > 0);
 
		} else if (AG_TIMEOUTS_QUEUED()) {
			/*
			 * Case 3: There are AG_Timeout(3) callbacks to run.
			 */
			AG_ProcessTimeouts(t2);
		} else {
			/*
			 * Case 4: Nothing to do, idle.
			 */
			AG_Delay(1);
		}
	}
}
 
int
main(int argc, char *argv[])
{
	AG_Window *win;
	char *driverSpec = NULL, *optArg;
	int c;
 
	while ((c = AG_Getopt(argc, argv, "?hd:", &optArg, NULL)) != -1) {
		switch (c) {
		case 'd':
			driverSpec = optArg;
			break;
		case '?':
		case 'h':
		default:
			printf("Usage: customeventloop [-d agar-driver-spec]\n");
			return (1);
		}
	}
 
	if (AG_InitCore("agar-customeventloop-demo", 0) == -1 ||
	    AG_InitGraphics(driverSpec) == -1) {
		fprintf(stderr, "%s\n", AG_GetError());
		return (1);
	}
	AG_BindGlobalKey(AG_KEY_ESCAPE, AG_KEYMOD_ANY, AG_QuitGUI);
 
	win = AG_WindowNew(0);
	AG_WindowSetCaption(win, "Agar custom event loop demo");
	AG_LabelNewPolled(win, AG_LABEL_EXPAND,
	    "Testing custom event loop\n"
	    "Frame rate = %d\n"
	    "Pressed key = %d\n"
	    "Clicked at %d,%d\n",
	    &curFPS, &pressedKey, &xClick, &yClick);
	AG_ButtonNewFn(win, AG_BUTTON_HFILL, "Quit", AGWINDETACH(win));
	AG_WindowSetGeometry(win, -1, -1, 300, 128);
	AG_WindowShow(win);
 
	MyEventLoop();
	AG_Destroy();
	return (0);
}

Custom Event Loop

From Agar

Example code

SEE ALSO

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