Add swap_interval support.

Again, mostly useful for 120Hz monitors, and/or playing content which is
a fraction of monitor refresh rate.

config.def.h

@@ -219,6 +219,10 @@ static const unsigned hard_sync_frames = 0;
 // Useful for 120 Hz monitors who want to play 60 Hz material with eliminated ghosting. video_refresh_rate should still be configured as if it is a 60 Hz monitor (divide refresh rate by 2).
 static bool black_frame_insertion = false;
 
+// Uses a custom swap interval for VSync.
+// Set this to effectively halve monitor refresh rate.
+static unsigned swap_interval = 1;
+
 // Threaded video. Will possibly increase performance significantly at cost of worse synchronization and latency.
 static const bool video_threaded = false;
 

frontend/menu/menu_common.h

@@ -119,6 +119,7 @@ typedef enum
    RGUI_SETTINGS_VIDEO_HARD_SYNC,
    RGUI_SETTINGS_VIDEO_HARD_SYNC_FRAMES,
    RGUI_SETTINGS_VIDEO_BLACK_FRAME_INSERTION,
+   RGUI_SETTINGS_VIDEO_SWAP_INTERVAL,
    RGUI_SETTINGS_VIDEO_REFRESH_RATE_AUTO,
    RGUI_SETTINGS_VIDEO_OPTIONS_LAST,
 #ifdef HAVE_SHADER_MANAGER

frontend/menu/rgui.c

@@ -605,6 +605,9 @@ static void render_text(rgui_handle_t *rgui)
             case RGUI_SETTINGS_VIDEO_BLACK_FRAME_INSERTION:
                strlcpy(type_str, g_settings.video.black_frame_insertion ? "ON" : "OFF", sizeof(type_str));
                break;
+            case RGUI_SETTINGS_VIDEO_SWAP_INTERVAL:
+               snprintf(type_str, sizeof(type_str), "%u", g_settings.video.swap_interval);
+               break;
             case RGUI_SETTINGS_VIDEO_HARD_SYNC_FRAMES:
                snprintf(type_str, sizeof(type_str), "%u", g_settings.video.hard_sync_frames);
                break;
@@ -1513,6 +1516,7 @@ static void rgui_settings_video_options_populate_entries(rgui_handle_t *rgui)
    rgui_list_push(rgui->selection_buf, "Hard GPU Sync", RGUI_SETTINGS_VIDEO_HARD_SYNC, 0);
    rgui_list_push(rgui->selection_buf, "Hard GPU Sync Frames", RGUI_SETTINGS_VIDEO_HARD_SYNC_FRAMES, 0);
    rgui_list_push(rgui->selection_buf, "Black Frame Insertion", RGUI_SETTINGS_VIDEO_BLACK_FRAME_INSERTION, 0);
+   rgui_list_push(rgui->selection_buf, "VSync Swap Interval", RGUI_SETTINGS_VIDEO_SWAP_INTERVAL, 0);
    rgui_list_push(rgui->selection_buf, "Estimated Monitor FPS", RGUI_SETTINGS_VIDEO_REFRESH_RATE_AUTO, 0);
 }
 
@@ -1958,6 +1962,36 @@ static int video_option_toggle_setting(rgui_handle_t *rgui, unsigned setting, rg
          }
          break;
 
+      case RGUI_SETTINGS_VIDEO_SWAP_INTERVAL:
+      {
+         unsigned old = g_settings.video.swap_interval;
+         switch (action)
+         {
+            case RGUI_ACTION_START:
+               g_settings.video.swap_interval = 1;
+               break;
+
+            case RGUI_ACTION_LEFT:
+               g_settings.video.swap_interval--;
+               break;
+
+            case RGUI_ACTION_RIGHT:
+            case RGUI_ACTION_OK:
+               g_settings.video.swap_interval++;
+               break;
+
+            default:
+               break;
+         }
+
+         g_settings.video.swap_interval = min(g_settings.video.swap_interval, 4);
+         g_settings.video.swap_interval = max(g_settings.video.swap_interval, 1);
+         if (old != g_settings.video.swap_interval && driver.video && driver.video_data)
+            video_set_nonblock_state_func(false); // This will update the current swap interval. Since we're in RGUI now, always apply VSync.
+
+         break;
+      }
+
       case RGUI_SETTINGS_VIDEO_HARD_SYNC_FRAMES:
          switch (action)
          {

general.h

@@ -160,6 +160,7 @@ struct settings
       bool vsync;
       bool hard_sync;
       bool black_frame_insertion;
+      unsigned swap_interval;
       unsigned hard_sync_frames;
       bool smooth;
       bool force_aspect;

gfx/context/drm_egl_ctx.c

@@ -93,6 +93,8 @@ static void sighandler(int sig)
 static void gfx_ctx_swap_interval(unsigned interval)
 {
    g_interval = interval;
+   if (interval > 1)
+      RARCH_WARN("[KMS/EGL]: Swap intervals > 1 currently not supported. Will use swap interval of 1.\n");
 }
 
 static void gfx_ctx_check_window(bool *quit,

gfx/d3d9/d3d9.cpp

@@ -145,7 +145,20 @@ void D3DVideo::make_d3dpp(const video_info_t &info, D3DPRESENT_PARAMETERS &d3dpp
 
    d3dpp.Windowed = g_settings.video.windowed_fullscreen || !info.fullscreen;
 
-   d3dpp.PresentationInterval = info.vsync ? D3DPRESENT_INTERVAL_ONE : D3DPRESENT_INTERVAL_IMMEDIATE;
+   if (info.vsync)
+   {
+      switch (g_settings.video.swap_interval)
+      {
+         default:
+         case 1: d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_ONE; break;
+         case 2: d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_TWO; break;
+         case 3: d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_THREE; break;
+         case 4: d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_FOUR; break;
+      }
+   }
+   else
+      d3dpp.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;
+
    d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
    d3dpp.hDeviceWindow = hWnd;
    d3dpp.BackBufferCount = 2;

gfx/gl.c

@@ -1628,7 +1628,7 @@ static void gl_set_nonblock_state(void *data, bool state)
 
    gl_t *gl = (gl_t*)data;
    (void)gl;
-   context_swap_interval_func(state ? 0 : 1);
+   context_swap_interval_func(state ? 0 : g_settings.video.swap_interval);
 }
 
 static bool resolve_extensions(gl_t *gl)

settings.c

@@ -169,6 +169,7 @@ void config_set_defaults(void)
    g_settings.video.hard_sync = hard_sync;
    g_settings.video.hard_sync_frames = hard_sync_frames;
    g_settings.video.black_frame_insertion = black_frame_insertion;
+   g_settings.video.swap_interval = swap_interval;
    g_settings.video.threaded = video_threaded;
    g_settings.video.smooth = video_smooth;
    g_settings.video.force_aspect = force_aspect;
@@ -493,6 +494,9 @@ bool config_load_file(const char *path)
       g_settings.video.hard_sync_frames = 3;
 
    CONFIG_GET_BOOL(video.black_frame_insertion, "video_black_frame_insertion");
+   CONFIG_GET_INT(video.swap_interval, "video_swap_interval");
+   g_settings.video.swap_interval = max(g_settings.video.swap_interval, 1);
+   g_settings.video.swap_interval = min(g_settings.video.swap_interval, 4);
    CONFIG_GET_BOOL(video.threaded, "video_threaded");
    CONFIG_GET_BOOL(video.smooth, "video_smooth");
    CONFIG_GET_BOOL(video.force_aspect, "video_force_aspect");
@@ -979,6 +983,7 @@ bool config_save_file(const char *path)
    config_set_bool(conf, "video_hard_sync", g_settings.video.hard_sync);
    config_set_int(conf, "video_hard_sync_frames", g_settings.video.hard_sync_frames);
    config_set_bool(conf, "video_black_frame_insertion", g_settings.video.black_frame_insertion);
+   config_set_int(conf, "video_swap_interval", g_settings.video.swap_interval);
    config_set_int(conf, "aspect_ratio_index", g_settings.video.aspect_ratio_idx);
    config_set_string(conf, "audio_device", g_settings.audio.device);
    config_set_bool(conf, "audio_rate_control", g_settings.audio.rate_control);