Big netcode refactor to fixed timestep

buildsettings.h

@@ -15,6 +15,7 @@
 #define UNLOCK_ALL
 #define INFINITE_RESOURCES
 #define NO_GRAVITY
+#define NO_SUNS
 
 #else
 

gamestate.c

@@ -521,10 +521,7 @@ static void grid_correct_for_holes(GameState *gs, struct Entity *grid)
     // could be a gap between boxes in the grid, separate into multiple grids
 
     // goal: create list of "real grids" from this grid that have boxes which are
-    // ONLY connected horizontally and vertically. whichever one of these "real grids"
-    // has the most blocks stays the current grid, so
-    // if a player is inhabiting this ship it stays that ship.
-    // The other "real grids" are allocated as new grids
+    // ONLY connected horizontally and vertically.
 
 #define MAX_SEPARATE_GRIDS 8
   EntityID separate_grids[MAX_SEPARATE_GRIDS] = {0};
@@ -533,7 +530,7 @@ static void grid_correct_for_holes(GameState *gs, struct Entity *grid)
   int processed_boxes = 0;
 
   int biggest_separate_grid_index = 0;
-  int biggest_separate_grid_length = 0;
+  uint32_t biggest_separate_grid_length = 0;
 
   // process all boxes into separate, but correctly connected, grids
   while (processed_boxes < num_boxes)
@@ -544,6 +541,8 @@ static void grid_correct_for_holes(GameState *gs, struct Entity *grid)
     assert(unprocessed->is_box);
     box_remove_from_boxes(gs, unprocessed); // no longer in the boxes list of the grid
 
+    uint32_t biggest_box_index = 0;
+
     // flood fill from this unprocessed box, adding each result to cur_separate_grid_index,
     // removing each block from the grid
     // https://en.wikipedia.org/wiki/Flood_fill
@@ -565,6 +564,11 @@ static void grid_correct_for_holes(GameState *gs, struct Entity *grid)
           cur_separate_grid_size++;
           processed_boxes++;
 
+          if (get_id(gs, N).index > biggest_box_index)
+          {
+            biggest_box_index = get_id(gs, N).index;
+          }
+
           cpVect cur_local_pos = entity_shape_pos(N);
           const cpVect dirs[] = {
               (cpVect){
@@ -619,9 +623,9 @@ static void grid_correct_for_holes(GameState *gs, struct Entity *grid)
       }
     }
 
-    if (cur_separate_grid_size > biggest_separate_grid_length)
+    if (biggest_box_index > biggest_separate_grid_length)
     {
-      biggest_separate_grid_length = cur_separate_grid_size;
+      biggest_separate_grid_length = biggest_box_index;
       biggest_separate_grid_index = cur_separate_grid_index;
     }
     cur_separate_grid_index++;
@@ -659,8 +663,14 @@ static void grid_correct_for_holes(GameState *gs, struct Entity *grid)
       cur = next;
     }
 
-    cpBodySetVelocity(new_grid->body, cpBodyGetVelocityAtWorldPoint(grid->body, (grid_com(new_grid))));
-    cpBodySetAngularVelocity(new_grid->body, entity_angular_velocity(grid));
+    // @Robust do the momentum stuff properly here so no matter which grid stays as the current grid,
+    // the *SAME RESULT* happens. VERY IMPORTANT for client side prediction to match what the server says.
+    // Tried to use something consistent on the server and client like current entity index but DID NOT WORK
+    if (sepgrid_i != biggest_separate_grid_index)
+    {
+      cpBodySetVelocity(new_grid->body, cpBodyGetVelocityAtWorldPoint(grid->body, (grid_com(new_grid))));
+      cpBodySetAngularVelocity(new_grid->body, entity_angular_velocity(grid) / fmax(1.0, cpvdist(entity_pos(new_grid), entity_pos(grid))));
+    }
   }
 }
 
@@ -746,19 +756,16 @@ void destroy(GameState *gs)
 {
   // can't zero out gs data because the entity memory arena is reused
   // on deserialization
-  for (size_t i = 0; i < gs->max_entities; i++)
+  for (size_t i = 0; i < gs->cur_next_entity; i++)
   {
     if (gs->entities[i].exists)
+    {
       entity_destroy(gs, &gs->entities[i]);
+      gs->entities[i] = (Entity){0};
+    }
   }
   cpSpaceFree(gs->space);
   gs->space = NULL;
-
-  for (size_t i = 0; i < gs->cur_next_entity; i++)
-  {
-    if (gs->entities[i].exists)
-      gs->entities[i] = (Entity){0};
-  }
   gs->cur_next_entity = 0;
 }
 // center of mass, not the literal position
@@ -1325,12 +1332,15 @@ SerMaybeFailure ser_server_to_client(SerState *ser, ServerToClient *s)
   GameState *gs = s->cur_gs;
 
   // completely reset and destroy all gamestate data
-  if (!ser->serializing)
+  PROFILE_SCOPE("Destroy old gamestate")
   {
-    // avoid a memset here very expensive. que rico!
-    destroy(gs);
-    initialize(gs, gs->entities, gs->max_entities * sizeof(*gs->entities));
-    gs->cur_next_entity = 0; // updated on deserialization
+    if (!ser->serializing)
+    {
+      // avoid a memset here very expensive. que rico!
+      destroy(gs);
+      initialize(gs, gs->entities, gs->max_entities * sizeof(*gs->entities));
+      gs->cur_next_entity = 0; // updated on deserialization
+    }
   }
 
   int cur_next_entity = 0;
@@ -1373,104 +1383,114 @@ SerMaybeFailure ser_server_to_client(SerState *ser, ServerToClient *s)
 
   if (ser->serializing)
   {
-    bool entities_done = false;
-    for (size_t i = 0; i < gs->cur_next_entity; i++)
+    PROFILE_SCOPE("Serialize entities")
     {
-      Entity *e = &gs->entities[i];
+      bool entities_done = false;
+      for (size_t i = 0; i < gs->cur_next_entity; i++)
+      {
+        Entity *e = &gs->entities[i];
 #define DONT_SEND_BECAUSE_CLOAKED(entity) (!ser->save_or_load_from_disk && ser->for_player != NULL && is_cloaked(gs, entity, ser->for_player))
 #define SER_ENTITY()       \
   SER_VAR(&entities_done); \
   SER_VAR(&i);             \
   SER_MAYBE_RETURN(ser_entity(ser, gs, e))
-      if (e->exists && !(ser->save_or_load_from_disk && e->no_save_to_disk) && !DONT_SEND_BECAUSE_CLOAKED(e))
-      {
-        if (!e->is_box && !e->is_grid)
-        {
-          SER_ENTITY();
-        }
-        if (e->is_grid)
+        if (e->exists && !(ser->save_or_load_from_disk && e->no_save_to_disk) && !DONT_SEND_BECAUSE_CLOAKED(e))
         {
-          bool serialized_grid_yet = false;
-          // serialize boxes always after bodies, so that by the time the boxes
-          // are loaded in the parent body is loaded in and can be referenced.
-          BOXES_ITER(gs, cur_box, e)
+          if (!e->is_box && !e->is_grid)
           {
-            bool this_box_in_range = ser->save_or_load_from_disk;
-            this_box_in_range |= ser->for_player == NULL;
-            this_box_in_range |= (ser->for_player != NULL && cpvdistsq(entity_pos(ser->for_player), entity_pos(cur_box)) < VISION_RADIUS * VISION_RADIUS); // only in vision radius
-            if (DONT_SEND_BECAUSE_CLOAKED(cur_box))
-              this_box_in_range = false;
-            if (cur_box->always_visible)
-              this_box_in_range = true;
-            if (this_box_in_range)
+            SER_ENTITY();
+          }
+          if (e->is_grid)
+          {
+            bool serialized_grid_yet = false;
+            // serialize boxes always after bodies, so that by the time the boxes
+            // are loaded in the parent body is loaded in and can be referenced.
+            BOXES_ITER(gs, cur_box, e)
             {
-              if (!serialized_grid_yet)
+              bool this_box_in_range = ser->save_or_load_from_disk;
+              this_box_in_range |= ser->for_player == NULL;
+              this_box_in_range |= (ser->for_player != NULL && cpvdistsq(entity_pos(ser->for_player), entity_pos(cur_box)) < VISION_RADIUS * VISION_RADIUS); // only in vision radius
+              if (DONT_SEND_BECAUSE_CLOAKED(cur_box))
+                this_box_in_range = false;
+              if (cur_box->always_visible)
+                this_box_in_range = true;
+              if (this_box_in_range)
               {
-                serialized_grid_yet = true;
-                SER_ENTITY();
-              }
+                if (!serialized_grid_yet)
+                {
+                  serialized_grid_yet = true;
+                  SER_ENTITY();
+                }
 
-              // serialize this box
-              EntityID cur_id = get_id(gs, cur_box);
-              SER_ASSERT(cur_id.index < gs->max_entities);
-              SER_VAR(&entities_done);
-              size_t the_index = (size_t)cur_id.index; // super critical. Type of &i is size_t. @Robust add debug info in serialization for what size the expected type is, maybe string nameof the type
-              SER_VAR_NAME(&the_index, "&i");
-              SER_MAYBE_RETURN(ser_entity(ser, gs, cur_box));
+                // serialize this box
+                EntityID cur_id = get_id(gs, cur_box);
+                SER_ASSERT(cur_id.index < gs->max_entities);
+                SER_VAR(&entities_done);
+                size_t the_index = (size_t)cur_id.index; // super critical. Type of &i is size_t. @Robust add debug info in serialization for what size the expected type is, maybe string nameof the type
+                SER_VAR_NAME(&the_index, "&i");
+                SER_MAYBE_RETURN(ser_entity(ser, gs, cur_box));
+              }
             }
           }
         }
-      }
 #undef SER_ENTITY
+      }
+      entities_done = true;
+      SER_VAR(&entities_done);
     }
-    entities_done = true;
-    SER_VAR(&entities_done);
   }
   else
   {
-    Entity *last_grid = NULL;
-    while (true)
+    PROFILE_SCOPE("Deserialize entities")
     {
-      bool entities_done = false;
-      SER_VAR(&entities_done);
-      if (entities_done)
-        break;
-      size_t next_index;
-      SER_VAR_NAME(&next_index, "&i");
-      SER_ASSERT(next_index < gs->max_entities);
-      SER_ASSERT(next_index >= 0);
-      Entity *e = &gs->entities[next_index];
-      e->exists = true;
-      // unsigned int possible_next_index = (unsigned int)(next_index + 2); // plus two because player entity refers to itself on deserialization
-      unsigned int possible_next_index = (unsigned int)(next_index + 1);
-      gs->cur_next_entity = gs->cur_next_entity < possible_next_index ? possible_next_index : gs->cur_next_entity;
-      SER_MAYBE_RETURN(ser_entity(ser, gs, e));
-
-      if (e->is_box)
+      Entity *last_grid = NULL;
+      while (true)
       {
-        SER_ASSERT(last_grid != NULL);
-        SER_ASSERT(get_entity(gs, e->shape_parent_entity) != NULL);
-        SER_ASSERT(last_grid == get_entity(gs, e->shape_parent_entity));
-        e->prev_box = (EntityID){0};
-        e->next_box = (EntityID){0};
-        box_add_to_boxes(gs, last_grid, e);
-      }
+        bool entities_done = false;
+        SER_VAR(&entities_done);
+        if (entities_done)
+          break;
+        size_t next_index;
+        SER_VAR_NAME(&next_index, "&i");
+        SER_ASSERT(next_index < gs->max_entities);
+        SER_ASSERT(next_index >= 0);
+        Entity *e = &gs->entities[next_index];
+        e->exists = true;
+        // unsigned int possible_next_index = (unsigned int)(next_index + 2); // plus two because player entity refers to itself on deserialization
+        unsigned int possible_next_index = (unsigned int)(next_index + 1);
+        gs->cur_next_entity = gs->cur_next_entity < possible_next_index ? possible_next_index : gs->cur_next_entity;
+        SER_MAYBE_RETURN(ser_entity(ser, gs, e));
 
-      if (e->is_grid)
-      {
-        e->boxes = (EntityID){0};
-        last_grid = e;
+        if (e->is_box)
+        {
+          SER_ASSERT(last_grid != NULL);
+          SER_ASSERT(get_entity(gs, e->shape_parent_entity) != NULL);
+          SER_ASSERT(last_grid == get_entity(gs, e->shape_parent_entity));
+          e->prev_box = (EntityID){0};
+          e->next_box = (EntityID){0};
+          box_add_to_boxes(gs, last_grid, e);
+        }
+
+        if (e->is_grid)
+        {
+          e->boxes = (EntityID){0};
+          last_grid = e;
+        }
       }
-    }
-    for (size_t i = 0; i < gs->cur_next_entity; i++)
-    {
-      Entity *e = &gs->entities[i];
-      if (!e->exists)
+
+      PROFILE_SCOPE("Add to free list")
       {
-        if (e->generation == 0)
-          e->generation = 1; // 0 generation reference is invalid, means null
-        e->next_free_entity = gs->free_list;
-        gs->free_list = get_id(gs, e);
+        for (size_t i = 0; i < gs->cur_next_entity; i++)
+        {
+          Entity *e = &gs->entities[i];
+          if (!e->exists)
+          {
+            if (e->generation == 0)
+              e->generation = 1; // 0 generation reference is invalid, means null
+            e->next_free_entity = gs->free_list;
+            gs->free_list = get_id(gs, e);
+          }
+        }
       }
     }
   }
@@ -1768,9 +1788,6 @@ enum CompassRotation facing_vector_to_compass(Entity *grid_to_transplant_to, Ent
   assert(grid_to_transplant_to->body != NULL);
   assert(grid_to_transplant_to->is_grid);
 
-  cpVect local_to_from = grid_world_to_local(grid_facing_vector_from, cpvadd(entity_pos(grid_facing_vector_from), facing_vector));
-  Log("local %f %f\n", local_to_from.x, local_to_from.y);
-
   cpVect from_target = cpvadd(entity_pos(grid_to_transplant_to), facing_vector);
   cpVect local_target = grid_world_to_local(grid_to_transplant_to, from_target);
   cpVect local_facing = local_target;
@@ -2118,30 +2135,13 @@ void exit_seat(GameState *gs, Entity *seat_in, Entity *p)
   cpBodySetVelocity(p->body, cpBodyGetVelocity(box_grid(seat_in)->body));
 }
 
-void process(struct GameState *gs, double dt, bool is_subframe)
+void process(struct GameState *gs, double dt)
 {
   PROFILE_SCOPE("Gameplay processing")
   {
     assert(gs->space != NULL);
 
-    PROFILE_SCOPE("subframe stuff")
-    {
-
-      if (is_subframe)
-      {
-        gs->subframe_time += dt;
-        while (gs->subframe_time > TIMESTEP)
-        {
-          gs->subframe_time -= TIMESTEP;
-          gs->tick++;
-        }
-      }
-      else
-      {
-        assert(gs->subframe_time == 0.0);
-        gs->tick++;
-      }
-    }
+    gs->tick++;
 
     PROFILE_SCOPE("sun gravity")
     {
@@ -2452,7 +2452,7 @@ void process(struct GameState *gs, double dt, bool is_subframe)
         if (!e->exists)
           continue;
 
-        PROFILE_SCOPE("instant death ")
+        // PROFILE_SCOPE("instant death")
         {
           cpFloat dist_from_center = cpvlengthsq((entity_pos(e)));
           if (e->body != NULL && dist_from_center > (INSTANT_DEATH_DISTANCE_FROM_CENTER * INSTANT_DEATH_DISTANCE_FROM_CENTER))
@@ -2484,8 +2484,8 @@ void process(struct GameState *gs, double dt, bool is_subframe)
           }
         }
 
-        // sun processing for this current entity
-        #if 0
+// sun processing for this current entity
+#ifndef NO_SUNS
         PROFILE_SCOPE("this entity sun processing")
         {
           SUNS_ITER(gs)
@@ -2517,7 +2517,7 @@ void process(struct GameState *gs, double dt, bool is_subframe)
             }
           }
         }
-        #endif
+#endif
 
         if (e->is_explosion)
         {
@@ -2557,7 +2557,7 @@ void process(struct GameState *gs, double dt, bool is_subframe)
 
         if (e->is_box)
         {
-          PROFILE_SCOPE("Box processing")
+          // PROFILE_SCOPE("Box processing")
           {
             if (e->is_platonic)
             {
@@ -2646,7 +2646,7 @@ void process(struct GameState *gs, double dt, bool is_subframe)
 
         if (e->is_grid)
         {
-          PROFILE_SCOPE("Grid processing")
+          // PROFILE_SCOPE("Grid processing")
           {
             Entity *grid = e;
             // calculate how much energy solar panels provide

main.c

@@ -58,6 +58,8 @@ static bool fullscreened = false;
 static bool picking_new_boxtype = false;
 
 static bool build_pressed = false;
+static double dilating_time_factor = 1.0;
+static double time_to_process = 0.0;
 static bool interact_pressed = false;
 #define MAX_MOUSEBUTTON (SAPP_MOUSEBUTTON_MIDDLE + 1)
 static bool mousedown[MAX_MOUSEBUTTON] = {0};
@@ -86,8 +88,6 @@ static ENetPeer *peer;
 static double zoom_target = 300.0;
 static double zoom = 300.0;
 static enum Squad take_over_squad = (enum Squad) - 1; // -1 means not taking over any squad
-static double target_prediction_time_factor = 1.0;
-static double current_time_ahead_of_server = 0.0;
 
 // images
 static sg_image image_itemframe;
@@ -1330,6 +1330,19 @@ static void ui(bool draw, double dt, double width, double height)
     sgp_pop_transform();
 }
 
+// returns zero vector if no player
+static cpVect my_player_pos()
+{
+  if (myentity() != NULL)
+  {
+    return entity_pos(myentity());
+  }
+  else
+  {
+    return (cpVect){0};
+  }
+}
+
 static void draw_dots(cpVect camera_pos, double gap)
 {
   set_color_values(1.0, 1.0, 1.0, 1.0);
@@ -1368,6 +1381,23 @@ static void draw_dots(cpVect camera_pos, double gap)
   }
 }
 
+void apply_this_tick_of_input_to_player(uint64_t tick_to_search_for)
+{
+  InputFrame *to_apply = NULL;
+  QUEUE_ITER(&input_queue, cur_header)
+  {
+    InputFrame *cur = (InputFrame *)cur_header->data;
+    if (cur->tick == tick(&gs))
+    {
+      to_apply = cur;
+      break;
+    }
+  }
+  if (to_apply != NULL && myplayer() != NULL)
+  {
+    myplayer()->input = *to_apply;
+  }
+}
 static cpVect get_global_hand_pos(cpVect world_mouse_pos, bool *hand_at_arms_length)
 {
   if (myentity() == NULL)
@@ -1395,7 +1425,7 @@ static void frame(void)
     double width = (float)sapp_width(), height = (float)sapp_height();
     double ratio = width / height;
     double exec_time = sapp_frame_count() * sapp_frame_duration();
-    double dt = (float)sapp_frame_duration();
+    double dt = sapp_frame_duration();
 
     // pressed input management
     {
@@ -1422,6 +1452,9 @@ static void frame(void)
     PROFILE_SCOPE("networking")
     {
       ENetEvent event;
+      uint64_t predicted_to_tick = tick(&gs); // modified on deserialization of game state
+      cpVect where_i_thought_id_be = my_player_pos();
+      bool applied_gamestate_packet = false;
       while (true)
       {
         int enet_status = enet_host_service(client, &event, 0);
@@ -1448,7 +1481,6 @@ static void frame(void)
             assert(LZO1X_MEM_DECOMPRESS == 0);
 
             ma_mutex_lock(&play_packets_mutex);
-            double predicted_to_time = time(&gs);
             ServerToClient msg = (ServerToClient){
                 .cur_gs = &gs,
                 .audio_playback_buffer = &packets_to_play,
@@ -1462,6 +1494,7 @@ static void frame(void)
               {
                 server_to_client_deserialize(&msg, decompressed,
                                              decompressed_max_len, false);
+                applied_gamestate_packet = true;
               }
               my_player_index = msg.your_player;
             }
@@ -1475,64 +1508,6 @@ static void frame(void)
             free(decompressed);
             enet_packet_destroy(event.packet);
 
-            PROFILE_SCOPE("Repredicting inputs")
-            {
-
-              double server_current_time = time(&gs);
-              double difference = predicted_to_time - server_current_time;
-              double target_prediction_time =
-                  (((double)peer->roundTripTime) / 1000.0) + TIMESTEP * 6.0;
-
-              // keeps it stable even though causes jumps occasionally
-              difference = fmax(difference, target_prediction_time);
-
-              double eps = TIMESTEP * 0.1;
-              if (predicted_to_time - time(&gs) < target_prediction_time - eps)
-              {
-                target_prediction_time_factor = 1.1;
-              }
-              else if (predicted_to_time - time(&gs) >
-                       target_prediction_time + eps * 2.0)
-              {
-                target_prediction_time_factor = 0.9;
-              }
-              else
-              {
-                target_prediction_time_factor = 1.0;
-              }
-
-              // re-predict the inputs
-              double time_to_repredict = (float)difference;
-              Log("Repredicting %f\n", time_to_repredict);
-
-              uint64_t start_prediction_time = stm_now();
-              if (time_to_repredict > 0.0)
-              {
-                while (time_to_repredict > TIMESTEP)
-                {
-                  if (stm_ms(stm_diff(stm_now(), start_prediction_time)) > MAX_MS_SPENT_REPREDICTING)
-                  {
-                    Log("Reprediction took longer than %f milliseconds, could only predict %f\n", MAX_MS_SPENT_REPREDICTING, time_to_repredict);
-                    break;
-                  }
-                  QUEUE_ITER(&input_queue, cur_header)
-                  {
-                    InputFrame *cur = (InputFrame *)cur_header->data;
-                    if (cur->tick == tick(&gs))
-                    {
-                      myplayer()->input = *cur;
-                      break;
-                    }
-                  }
-                  process(&gs, TIMESTEP, false);
-                  time_to_repredict -= TIMESTEP;
-                }
-                process(&gs, time_to_repredict, true);
-                time_to_repredict = 0.0;
-              }
-
-              current_time_ahead_of_server = time(&gs) - server_current_time;
-            }
             break;
           }
 
@@ -1554,6 +1529,64 @@ static void frame(void)
           break;
         }
       }
+
+      // only repredict inputs on the most recent server authoritative packet
+      PROFILE_SCOPE("Repredicting inputs")
+      {
+        if (applied_gamestate_packet)
+        {
+          uint64_t server_current_tick = tick(&gs);
+
+          uint64_t ticks_should_repredict = predicted_to_tick - server_current_tick;
+
+          uint64_t healthy_num_ticks_ahead = (uint64_t)ceil((((double)peer->roundTripTime) / 1000.0) / TIMESTEP) + 6;
+
+          // keeps it stable even though causes jumps occasionally
+          uint64_t ticks_to_repredict = ticks_should_repredict;
+
+          if (ticks_should_repredict < healthy_num_ticks_ahead - 1)
+          {
+            dilating_time_factor = 1.1;
+          }
+          else if (ticks_should_repredict > healthy_num_ticks_ahead + 1)
+          {
+            dilating_time_factor = 0.1;
+          }
+          else
+          {
+            dilating_time_factor = 1.0;
+          }
+
+          // snap in dire cases
+          if (ticks_should_repredict < healthy_num_ticks_ahead - TICKS_BEHIND_DO_SNAP)
+          {
+            Log("Snapping\n");
+            ticks_to_repredict = healthy_num_ticks_ahead;
+          }
+
+          uint64_t start_prediction_time = stm_now();
+          while (ticks_to_repredict > 0)
+          {
+            if (stm_ms(stm_diff(stm_now(), start_prediction_time)) > MAX_MS_SPENT_REPREDICTING)
+            {
+              Log("Reprediction took longer than %f milliseconds, needs to repredict %llu more ticks\n", MAX_MS_SPENT_REPREDICTING, ticks_to_repredict);
+              break;
+            }
+            apply_this_tick_of_input_to_player(tick(&gs));
+            process(&gs, TIMESTEP);
+            ticks_to_repredict -= 1;
+          }
+
+          cpVect where_i_am = my_player_pos();
+
+          double reprediction_error = cpvdist(where_i_am, where_i_thought_id_be);
+          InputFrame *biggest_frame = (InputFrame *)queue_most_recent_element(&input_queue);
+          if (reprediction_error >= 0.1)
+          {
+            Log("Big reprediction error %llu\n", biggest_frame->tick);
+          }
+        }
+      }
     }
 
     // gameplay
@@ -1647,38 +1680,53 @@ static void frame(void)
           cur_input_frame.build_rotation = cur_editing_rotation;
         }
 
-        // "commit" the input. each input must be on a successive tick.
-        if (tick(&gs) > last_input_committed_tick)
-        {
-          cur_input_frame.tick = tick(&gs);
-          last_input_committed_tick = tick(&gs);
+        // in client side prediction, only process the latest input in the queue, not
+        // the one currently constructing.
 
-          InputFrame *to_push_to = queue_push_element(&input_queue);
-          if (to_push_to == NULL)
+        time_to_process += dt * dilating_time_factor;
+
+        cpVect before = my_player_pos();
+        do
+        {
+          // "commit" the input. each input must be on a successive tick.
+          if (tick(&gs) > last_input_committed_tick)
           {
-            InputFrame *to_discard = queue_pop_element(&input_queue);
-            (void)to_discard;
-            to_push_to = queue_push_element(&input_queue);
-            assert(to_push_to != NULL);
-          }
+            cur_input_frame.tick = tick(&gs);
+            last_input_committed_tick = tick(&gs);
 
-          *to_push_to = cur_input_frame;
+            InputFrame *to_push_to = queue_push_element(&input_queue);
+            if (to_push_to == NULL)
+            {
+              InputFrame *to_discard = queue_pop_element(&input_queue);
+              (void)to_discard;
+              to_push_to = queue_push_element(&input_queue);
+              assert(to_push_to != NULL);
+            }
 
-          if (myplayer() != NULL)
-            myplayer()->input =
-                cur_input_frame; // for the client side prediction!
+            *to_push_to = cur_input_frame;
 
-          cur_input_frame = (InputFrame){0};
-          cur_input_frame.take_over_squad =
-              -1; // @Robust make this zero initialized
-        }
+            if (myplayer() != NULL)
+              myplayer()->input =
+                  cur_input_frame; // for the client side prediction!
 
-        // in client side prediction, only process the latest in the queue, not
-        // the one currently constructing.
-        static double prediction_time_factor = 1.0;
-        prediction_time_factor = lerp(prediction_time_factor,
-                                      target_prediction_time_factor, dt * 3.0);
-        process(&gs, dt * prediction_time_factor, true);
+            cur_input_frame = (InputFrame){0};
+            cur_input_frame.take_over_squad = -1; // @Robust make this zero initialized
+          }
+
+          if (time_to_process >= TIMESTEP)
+          {
+            uint64_t tick_to_predict = tick(&gs);
+            apply_this_tick_of_input_to_player(tick_to_predict);
+            process(&gs, TIMESTEP);
+            time_to_process -= TIMESTEP;
+          }
+        } while (time_to_process >= TIMESTEP);
+        cpVect after = my_player_pos();
+
+        // use theses variables to suss out reprediction errors, enables you to 
+        // breakpoint on when they happen
+        (void)before;
+        (void)after;
 
         static int64_t last_sent_input_time = 0;
         if (stm_sec(stm_diff(stm_now(), last_sent_input_time)) >

server.c

@@ -325,7 +325,7 @@ void server(void *info_raw)
             }
           }
 
-          process(&gs, TIMESTEP, false);
+          process(&gs, TIMESTEP);
           total_time -= TIMESTEP;
         }
       }

types.h

@@ -76,6 +76,7 @@
 #define VOIP_DISTANCE_WHEN_CANT_HEAR (VISION_RADIUS * 0.8f)
 
 // multiplayer
+#define TICKS_BEHIND_DO_SNAP 6 // when this many ticks behind, instead of dilating time SNAP to the healthy ticks ahead
 #define MAX_MS_SPENT_REPREDICTING 30.0f
 #define TIME_BETWEEN_SEND_GAMESTATE (1.0f / 20.0f)
 #define TIME_BETWEEN_INPUT_PACKETS (1.0f / 20.0f)
@@ -422,7 +423,7 @@ void destroy(struct GameState *gs);
 void process_fixed_timestep(GameState *gs);
 // if is subframe, doesn't always increment the tick. When enough
 // subframe time has been processed, increments the tick
-void process(struct GameState *gs, double dt, bool is_subframe); // does in place
+void process(struct GameState *gs, double dt); // does in place
 Entity *closest_box_to_point_in_radius(struct GameState *gs, cpVect point, double radius, bool (*filter_func)(Entity *));
 uint64_t tick(struct GameState *gs);
 double time(GameState *gs);