[PATCH v3 weston] gears: fix invalid calculation of the first FPS

[Nils Chr. Brause]

On Sun, Aug 10, 2014 at 4:47 PM, Ryo Munakata <ryomnktml at gmail.com> wrote:

> 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.
> ---
>  clients/gears.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/clients/gears.c b/clients/gears.c
> index 95f0bb2..1fb77e0 100644
> --- a/clients/gears.c
> +++ b/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>
> @@ -208,8 +209,13 @@ static void
>  update_fps(struct gears *gears, uint32_t time)
>  {
>         long diff_ms;
> +       static bool first_call = true;
>
> -       gears->frames++;
> +       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);
>

Perfect! :)

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

 --
> 2.0.4
>
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