Fix and improve fast-forward (frame skip) (#4989)

Author: jwt27

src/bflib_datetm.cpp

@@ -58,7 +58,7 @@ void initial_time_point()
   game.process_turn_time = 1.0; // Begin initial turn as soon as possible (like original game)
 }
 
-long double get_time_tick_ns()
+int64_t get_time_tick_ns()
 {
   return TimeTickNs;
 }
@@ -95,22 +95,6 @@ int get_trigger_time_measurement_fps(struct TriggerTimeMeasurement *trigger)
   return cnt;
 }
 
-
-float get_delta_time()
-{
-    // Allow frame skip to work correctly when delta time is enabled
-    if ( (game.frame_skip != 0) && ((get_gameturn() % game.frame_skip) != 0)) {
-        return 1.0;
-    }
-    long double frame_time_in_nanoseconds = std::chrono::duration_cast<std::chrono::nanoseconds>(TimeNow - delta_time_previous_timepoint).count();
-    delta_time_previous_timepoint = TimeNow;
-    float calculated_delta_time = (frame_time_in_nanoseconds/1000000000.0) * turns_per_second;
-    if (calculated_delta_time > 1.0) { // Fix for when initially loading the map, frametime takes too long. Possibly other circumstances too.
-        calculated_delta_time = 1.0;
-    }
-    return calculated_delta_time;
-}
-
 void frametime_set_all_measurements_to_be_displayed()
 {
     // Display the frametime of the previous frame only, not the current frametime. Drawing "frametime_current" is a bad idea because frametimes are displayed on screen half-way through the rest of the measurements.

src/bflib_datetm.h

@@ -95,11 +95,10 @@ struct FrametimeMeasurements {
 
 extern int debug_display_frametime;
 extern void initial_time_point();
-extern long double get_time_tick_ns();
+extern int64_t get_time_tick_ns();
 extern void frametime_start_measurement(int frametime_kind);
 extern void frametime_end_measurement(int frametime_kind);
 extern void framerate_measurement_capture(int framerate_kind);
-extern float get_delta_time();
 
 extern struct FrametimeMeasurements frametime_measurements;
 

src/engine_render.c

@@ -534,17 +534,17 @@ extern float interpolate_time;  // main.cpp
 
 float interpolate(float previous, float current)
 {
-    if (is_feature_on(Ft_DeltaTime) == false || game.frame_skip > 0) {
+    if (! is_feature_on(Ft_DeltaTime))
         return current;
-    }
+
     return LbLerp(previous, current, interpolate_time);
 }
 
 float interpolate_angle(float previous, float current)
 {
-    if (is_feature_on(Ft_DeltaTime) == false || game.frame_skip > 0) {
+    if (! is_feature_on(Ft_DeltaTime))
         return current;
-    }
+
     return lerp_angle(previous, current, interpolate_time);
 }
 

src/front_input.c

@@ -98,6 +98,8 @@ struct GuiLayer gui_layer = {GuiLayer_Default};
 
 TbBool first_person_see_item_desc = false;
 
+static TbBool move_camera_this_turn;
+
 long old_mx;
 long old_my;
 
@@ -2143,10 +2145,6 @@ static short get_map_action_inputs(void)
     }
 }
 
-// TODO: Might want to initiate this in main() and pass a reference to it
-// rather than using this global variable. But this works.
-int global_frameskipTurn = 0;
-
 static void get_isometric_or_front_view_mouse_inputs(struct Packet *pckt,int rotate_pressed,TbBool mods_used)
 {
     // Reserve the scroll wheel for the resurrect and transfer creature specials
@@ -2185,13 +2183,8 @@ static void get_isometric_or_front_view_mouse_inputs(struct Packet *pckt,int rot
         }
     }
     // Only pan the camera as often as normal despite frameskip
-    if (game.frame_skip > 0)
-    {
-        TbBool moveTheCamera = (global_frameskipTurn == 0);
-        global_frameskipTurn++;
-        if (global_frameskipTurn > game.frame_skip) global_frameskipTurn = 0;
-        if (!moveTheCamera) return;
-    }
+    if (! move_camera_this_turn)
+        return;
     // Camera Panning : mouse at window edge scrolling feature
     if (!LbIsMouseActive())
     {
@@ -2255,15 +2248,7 @@ static void get_isometric_view_nonaction_inputs(void)
 
     get_isometric_or_front_view_mouse_inputs(packet, rotate_pressed, no_mods);
     // Only update the camera as often as normal despite frameskip
-    TbBool moveTheCamera = true;
-    if (game.frame_skip > 0)
-    {
-        moveTheCamera = (global_frameskipTurn == 0);
-        global_frameskipTurn++;
-        if (global_frameskipTurn > game.frame_skip)
-            global_frameskipTurn = 0;
-    }
-    if (moveTheCamera)
+    if (move_camera_this_turn)
     {
         if (rotate_pressed)
         {
@@ -2346,15 +2331,7 @@ static void get_front_view_nonaction_inputs(void)
 
     get_isometric_or_front_view_mouse_inputs(pckt,rotate_pressed,no_mods);
     // Only update the camera as often as normal despite frameskip
-    TbBool moveTheCamera = true;
-    if (game.frame_skip > 0)
-    {
-        moveTheCamera = (global_frameskipTurn == 0);
-        global_frameskipTurn++;
-        if (global_frameskipTurn > game.frame_skip)
-            global_frameskipTurn = 0;
-    }
-    if (moveTheCamera)
+    if (move_camera_this_turn)
     {
         if (rotate_pressed)
         {
@@ -2870,6 +2847,8 @@ static TbBool active_menu_functions_while_paused(void)
  */
 static short get_inputs(void)
 {
+    move_camera_this_turn = game.frame_skip == 0 || game.play_gameturn % game.frame_skip == 0;
+
     if ((game.mode_flags & MFlg_IsDemoMode) != 0)
     {
         SYNCDBG(5,"Starting for demo mode");

src/frontend.cpp

@@ -97,7 +97,6 @@ extern "C" {
 #endif
 
 extern long double last_draw_completed_time;
-long double get_time_tick_ns();
 /******************************************************************************/
 TbClockMSec gui_message_timeout = 0;
 char gui_message_text[TEXT_BUFFER_LENGTH];

src/main.cpp

@@ -3261,7 +3261,7 @@ short display_should_be_updated_this_turn(void)
     if ( (game.turns_fastforward == 0) && (!game.packet_loading_in_progress) )
     {
       find_frame_rate();
-      if ( (game.frame_skip == 0) || ((get_gameturn() % game.frame_skip) == 0))
+      if ( is_feature_on(Ft_DeltaTime) || (game.frame_skip == 0) || ((get_gameturn() % game.frame_skip) == 0))
         return true;
     } else
     if ( ((get_gameturn() & 0x3F)==0) ||
@@ -3421,12 +3421,32 @@ static bool use_delta_time()
     return is_feature_on(Ft_DeltaTime) || network_is_active();
 }
 
+static void update_frontend_delta_time()
+{
+    static int64_t prev = 0;
+    const int64_t now = get_time_tick_ns();
+    const int64_t ns = now - prev;
+    prev = now;
+    const long double dt = ns / 1e9L * turns_per_second;
+    game.delta_time = min(max(dt, 0.L), 1.L);
+}
+
 static void update_gameplay_delta_time()
 {
     if (use_delta_time()) {
-        long double process_delta_time = get_delta_time() * multiplayer_clock_adjust;
-        time_since_last_draw += process_delta_time;
-        game.process_turn_time += process_delta_time;
+        static int64_t prev = 0;
+        const int64_t now = get_time_tick_ns();
+        const int64_t ns = now - prev;
+        prev = now;
+
+        const long double dt = min(max(ns / 1e9L * turns_per_second, 0.L), 1.L);
+
+        game.process_turn_time += dt * multiplayer_clock_adjust * max(game.frame_skip, 1);
+
+        // This sets game.delta_time, which is used to pace locally-displayed
+        // things (eg. tooltip scroll speed).  It should not be affected by
+        // multiplayer clock adjustment or frameskip.
+        time_since_last_draw += dt;
     } else {
         // Set to 1 so that these variables don't affect anything. (if something is multiplied by 1 it doesn't change)
         time_since_last_draw = 1;
@@ -3437,6 +3457,11 @@ static void update_gameplay_delta_time()
 
 static void gameplay_loop_draw()
 {
+    update_gameplay_delta_time();
+
+    if (game.process_turn_time > 1.0 && time_since_last_draw < 1.0)
+        do_draw = false;
+
     if (is_feature_on(Ft_DeltaTime) && ! network_is_active())
     {
         frametime_start_measurement(Frametime_Sleep);
@@ -3546,8 +3571,8 @@ static void gameplay_loop_logic()
     exchange_packets();
 
     update_gameplay_delta_time();
-    if (game.process_turn_time > 2.0)
-        game.process_turn_time = 2.0;
+    if (game.process_turn_time > turns_per_second + 1)
+        game.process_turn_time = turns_per_second + 1;
 
     // Adjust client time scaling
     if (netstate.my_id != SERVER_ID && network_is_active())
@@ -3619,9 +3644,11 @@ extern "C" void network_yield_waiting_gameplay_packets()
 {
     do_draw = true;
     poll_inputs();
+    gameplay_loop_draw();
     update_gameplay_delta_time();
-    if (game.process_turn_time <= 1.0 || time_since_last_draw > 1.0)
-        gameplay_loop_draw();
+    // Reduce game speed during lag spikes.
+    if (game.process_turn_time > 2.0)
+        game.process_turn_time = 2.0;
 }
 
 extern "C" void update_velocity(void);
@@ -3630,7 +3657,7 @@ extern "C" void fronttorture_update(void);
 
 extern "C" void network_yield_draw_frontend()
 {
-    game.delta_time = get_delta_time();
+    update_frontend_delta_time();
     if (frontend_menu_state == FeSt_NETLAND_VIEW) {
         check_mouse_scroll();
         update_velocity();
@@ -3943,7 +3970,7 @@ static TbBool wait_at_frontend(void)
         fade_palette_in = 0;
       } else {
         if (is_feature_on(Ft_DeltaTime) == true && should_use_delta_time_on_menu()) {
-          game.delta_time = get_delta_time();
+          update_frontend_delta_time();
         } else {
           int32_t frame_time;
           frame_time = max(1, 1000 / turns_per_second);