Add support for fast forward frame limiting.

config.def.h

@@ -381,6 +381,9 @@ static const bool savestate_auto_load = true;
 // Slowmotion ratio.
 static const float slowmotion_ratio = 3.0;
 
+// Maximum fast forward ratio (Negative => no limit).
+static const float fastforward_ratio = -1.0;
+
 // Enable stdin/network command interface
 static const bool network_cmd_enable = false;
 static const uint16_t network_cmd_port = 55355;

general.h

@@ -264,6 +264,7 @@ struct settings
    unsigned rewind_granularity;
 
    float slowmotion_ratio;
+   float fastforward_ratio;
 
    bool pause_nonactive;
    unsigned autosave_interval;
@@ -367,6 +368,12 @@ struct global
 
    unsigned state_slot;
 
+   struct
+   {
+      rarch_time_t minimum_frame_time;
+      rarch_time_t last_frame_time;
+   } frame_limit;
+
    struct
    {
       struct retro_system_info info;

retroarch.c

@@ -2819,6 +2819,8 @@ void rarch_init_system_info(void)
 static void init_system_av_info(void)
 {
    pretro_get_system_av_info(&g_extern.system.av_info);
+   g_extern.frame_limit.last_frame_time = rarch_get_time_usec();
+   g_extern.frame_limit.minimum_frame_time = (rarch_time_t)roundf(1000000.0f / (g_extern.system.av_info.timing.fps * g_settings.fastforward_ratio));
 }
 
 static void verify_api_version(void)
@@ -3021,6 +3023,23 @@ static inline void update_frame_time(void)
    g_extern.system.frame_time.callback(delta);
 }
 
+static inline void limit_frame_time(void)
+{
+   if (g_settings.fastforward_ratio < 0.0f)
+      return;
+
+   rarch_time_t current = rarch_get_time_usec();
+   rarch_time_t target = g_extern.frame_limit.last_frame_time + g_extern.frame_limit.minimum_frame_time;
+   rarch_time_t to_sleep_ms = (target - current) / 1000;
+   if (to_sleep_ms > 0)
+   {
+      rarch_sleep(to_sleep_ms);
+      g_extern.frame_limit.last_frame_time += g_extern.frame_limit.minimum_frame_time; // Combat jitter a bit.
+   }
+   else
+      g_extern.frame_limit.last_frame_time = rarch_get_time_usec();
+}
+
 bool rarch_main_iterate(void)
 {
 #ifdef HAVE_DYLIB
@@ -3065,6 +3084,7 @@ bool rarch_main_iterate(void)
 
    update_frame_time();
    pretro_run();
+   limit_frame_time();
 
 #ifdef HAVE_BSV_MOVIE
    if (g_extern.bsv.movie)

retroarch.cfg

@@ -461,6 +461,12 @@
 # Slowmotion ratio. When slowmotion, game will slow down by factor.
 # slowmotion_ratio = 3.0
 
+# The maximum rate at which games will be run when using fast forward. (E.g. 5.0 for 60 fps game => 300 fps cap).
+# RetroArch will go to sleep to ensure that the maximum rate will not be exceeded.
+# Do not rely on this cap to be perfectly accurate.
+# A negative ratio equals no FPS cap.
+# fastforward_ratio = -1.0
+
 # Enable stdin/network command interface.
 # network_cmd_enable = false
 # network_cmd_port = 55355

settings.c

@@ -209,6 +209,7 @@ void config_set_defaults(void)
    g_settings.rewind_buffer_size = rewind_buffer_size;
    g_settings.rewind_granularity = rewind_granularity;
    g_settings.slowmotion_ratio = slowmotion_ratio;
+   g_settings.fastforward_ratio = fastforward_ratio;
    g_settings.pause_nonactive = pause_nonactive;
    g_settings.autosave_interval = autosave_interval;
 
@@ -678,6 +679,8 @@ bool config_load_file(const char *path)
    if (g_settings.slowmotion_ratio < 1.0f)
       g_settings.slowmotion_ratio = 1.0f;
 
+   CONFIG_GET_FLOAT(fastforward_ratio, "fastforward_ratio");
+
    CONFIG_GET_BOOL(pause_nonactive, "pause_nonactive");
    CONFIG_GET_INT(autosave_interval, "autosave_interval");