forked from 0ad/0ad
151 lines
4.1 KiB
C++
Executable File
151 lines
4.1 KiB
C++
Executable File
//
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// Copyright (c) 2003 Jan Wassenberg
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// Contact info:
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// Jan.Wassenberg@stud.uni-karlsruhe.de
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// http://www.stud.uni-karlsruhe.de/~urkt/
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#include "precompiled.h"
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#include "lib.h"
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#include "timer.h"
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#include <math.h>
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// wrapper over gettimeofday, instead of emulating it for Windows,
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// because double return type allows higher resolution (e.g. if using TSC),
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// and gettimeofday is not guaranteed to be monotonic.
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double get_time()
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{
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double t;
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#ifdef HAVE_CLOCK_GETTIME
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static struct timespec start;
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struct timespec ts;
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if(!start.tv_sec)
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clock_gettime(CLOCK_REALTIME, &start);
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clock_gettime(CLOCK_REALTIME, &ts);
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t = (ts.tv_sec - start.tv_sec) + (ts.tv_nsec - start.tv_nsec)*1e-9;
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#elif defined(HAVE_GETTIMEOFDAY)
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static struct timeval start;
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struct timeval cur;
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if(!start.tv_sec)
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gettimeofday(&start, 0);
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gettimeofday(&cur, 0);
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t = (cur.tv_sec - start.tv_sec) + (cur.tv_usec - start.tv_usec)*1e-6;
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#else
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#error "get_time: add timer implementation for this platform!"
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#endif
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// make sure time is monotonic (never goes backwards)
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static double t_last;
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if(t_last != 0.0 && t < t_last)
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t = t_last;
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return t;
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}
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double timer_res()
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{
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#ifdef HAVE_CLOCK_GETTIME
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struct timespec res;
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clock_getres(CLOCK_REALTIME, &res);
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return res.tv_nsec * 1e-9;
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#else
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// guess millisecond-class
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return 1e-3;
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#endif
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}
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// calculate fps (call once per frame)
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// several smooth filters:
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// - throw out single spikes / dips
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// - average via small history buffer
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// - update final value iff the difference (% or absolute) is too great,
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// or if the change is consistent with the trend over the last few frames.
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//
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// => less fluctuation, but rapid tracking.
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// filter values are tuned for 100 FPS.
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int fps = 0;
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void calc_fps()
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{
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// history buffer - smooth out slight variations
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#define H 10 // # buffer entries
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static float fps_sum = 0; // sum of last H frames' cur_fps
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static float fps_hist[H]; // last H frames' cur_fps
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// => don't need to re-average every time
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static uint head = 0; // oldest entry in fps_hist
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// must be unsigned, b/c we do (head-1)%H
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// get elapsed time [s] since last frame; approximate current fps
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static double last_t;
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double t = get_time();
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float cur_fps = 30.0f; // start value => history converges faster
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if(last_t != 0.0)
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cur_fps = 1.0f / (float)(t-last_t); // = 1 / elapsed time
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last_t = t;
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// calculate fps activity over 3 frames (used below to prevent fluctuation)
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// -1: decreasing, +1: increasing, 0: neither or fluctuating
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float h1 = fps_hist[(head-1)%H]; // last frame's cur_fps
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float h2 = fps_hist[(head-2)%H]; // 2nd most recent frame's cur_fps
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int trend = 0;
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if(h2 > h1 && h1 > cur_fps) // decreasing
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trend = -1;
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else if(cur_fps < h1 && h1 < h2) // increasing
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trend = 1;
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// ignore onetime skips in fps (probably page faults or similar)
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static int ignored;
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if(fabs(h1-cur_fps) > .05f*h1 && // > 5% difference
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!ignored++) // was it first value we're discarding?
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return; // yes: don't update fps_hist/fps
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ignored = 0; // either value ok, or it wasn't a fluke - reset counter
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// remove oldest cur_fps value in fps_hist from the sum
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// and add cur_fps; also insert cur_fps in fps_hist
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fps_sum -= fps_hist[head];
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fps_sum += (fps_hist[head] = cur_fps);
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head = (head+1)%H;
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// update fps counter if update threshold is exceeded
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const float avg_fps = fps_sum / H;
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const float d_avg = avg_fps-fps;
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const float max_diff = fminf(5.f, 0.05f*fps);
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if((trend > 0 && (avg_fps > fps || d_avg < -4.f)) || // going up, or large drop
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(trend < 0 && (avg_fps < fps || d_avg > 4.f)) || // going down, or large raise
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(fabs(d_avg) > max_diff)) // significant difference
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fps = (int)avg_fps;
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}
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