gears: fix invalid calculation of the first FPS

At the calculation of the first FPS, gears has initialized last
FPS time with gettimeofday().
But the callback_data passed in the callback of wl_surface_frame()
is the current time, in milliseconds, with an undefined base.
Because of this subtracting last FPS time from callback_data makes no sense.
 For example, below is the result of running weston-gears on weston with
drm backend:

$ weston-gears
Warning: FPS count is limited by the wayland compositor or monitor refresh rate
1 frames in 1094460.125 seconds =  0.000 FPS
301 frames in  5.016 seconds = 60.008 FPS
301 frames in  5.016 seconds = 60.008 FPS
301 frames in  5.016 seconds = 60.008 FPS

As you can see, the the first FPS value is something odd.

This patch fixes it by initializing last FPS time with the callback_data passed in
the first callback.

Reviewed-by: Nils Chr. Brause <nilschrbrause@gmail.com>

clients/gears.c

@@ -23,6 +23,7 @@
 #include "config.h"
 
 #include <stdint.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -208,7 +209,12 @@ static void
 update_fps(struct gears *gears, uint32_t time)
 {
 	long diff_ms;
+	static bool first_call = true;
 
+	if (first_call) {
+		gears->last_fps = time;
+		first_call = false;
+	} else
 		gears->frames++;
 
 	diff_ms = time - gears->last_fps;
@@ -398,7 +404,6 @@ gears_create(struct display *display)
 {
 	const int width = 450, height = 500;
 	struct gears *gears;
-	struct timeval tv;
 	int i;
 
 	gears = zalloc(sizeof *gears);
@@ -437,8 +442,6 @@ gears_create(struct display *display)
 	gears->view.rotx = 20.0;
 	gears->view.roty = 30.0;
 
-	gettimeofday(&tv, NULL);
-	gears->last_fps = tv.tv_sec * 1000 + tv.tv_usec / 1000;
 	printf("Warning: FPS count is limited by the wayland compositor or monitor refresh rate\n");
 
 	glEnable(GL_NORMALIZE);