Rewind improvements (#91)

* Prevent immediate deletion of restored key frames

Now, key frames will only be deleted if the user rewinds within less than 0.6 seconds (21 tics, give or take one tic) since the last rewind.

* Fix off-by-one error in countdown

There was one extra tic between key-frame saves, so they would be saved at e.g. 0:00.06, 0:01.09, 0:02.11 and so on.

* Keep key-framing time aligned

Now, key frames should always be saved at .06 seconds, regardless of level changes, save loads, and interval changes.

* Update documentation

CHANGELOG.md

@@ -6,6 +6,9 @@
 
 ## Changes
 
+- **Rewind improvements:**
+  - Only delete key frames when rewinding within less than 0.6 seconds since the last rewind
+  - "Aligned" key-framing time
 - **Support for _Milestone Completion Announcements_ in multiplayer**
 
 ## Bug Fixes

src/g_game.c

@@ -1058,6 +1058,9 @@ static void G_DoLoadLevel(void)
 
   // [Nugget] ----------------------------------------------------------------
 
+  // Rewind
+  G_SetRewindCountdown(0);
+
   // Minimap
   if (minimap_was_on) {
     AM_ChangeMode(AM_MINI);
@@ -2665,6 +2668,12 @@ static void G_DoLoadGame(void)
   st_health = players[displayplayer].health;
   st_armor  = players[displayplayer].armorpoints;
 
+  // [Nugget] Rewind:
+  // Just like with `G_DoRewind`,
+  // this is called before the countdown decrement in `G_Ticker()`,
+  // so add 1 to keep it aligned
+  G_SetRewindCountdown(((rewind_interval * TICRATE) + 1) - ((leveltime - 1) % (rewind_interval * TICRATE)));
+
   if (setsizeneeded)
     R_ExecuteSetViewSize();
 
@@ -2697,9 +2706,9 @@ static void G_DoLoadGame(void)
 
 // [Nugget] Rewind /----------------------------------------------------------
 
-void G_ResetRewindCountdown(void)
+void G_SetRewindCountdown(int value)
 {
-  rewind_countdown = rewind_interval * TICRATE;
+  rewind_countdown = value;
 }
 
 static void G_SaveKeyFrame(void)
@@ -2814,14 +2823,30 @@ static void G_SaveKeyFrame(void)
     rewind_on = false;
   }
 
-  G_ResetRewindCountdown();
+  G_SetRewindCountdown(rewind_interval * TICRATE);
 
   Z_Free(savebuffer);
   savebuffer = save_p = NULL;
 }
 
 static void G_DoRewind(void)
 {
+  static int last_rewind_time = 0;
+
+  if ((0 <= keyframe_index - 1)
+      && (gametic - last_rewind_time <= 21)) // 0.6 seconds
+  {
+    keyframe_index--;
+
+    Z_Free(keyframe_list_tail->frame);
+
+    keyframe_list_tail = keyframe_list_tail->prev;
+    Z_Free(keyframe_list_tail->next);
+    keyframe_list_tail->next = NULL;
+  }
+
+  last_rewind_time = gametic;
+
   int length, i;
 
   I_SetFastdemoTimer(false);
@@ -2944,18 +2969,9 @@ static void G_DoRewind(void)
 
   displaymsg("Restored key frame %i", keyframe_index);
 
-  if (0 <= keyframe_index - 1)
-  {
-    keyframe_index--;
-
-    Z_Free(savebuffer);
-
-    keyframe_list_tail = keyframe_list_tail->prev;
-    Z_Free(keyframe_list_tail->next);
-    keyframe_list_tail->next = NULL;
-  }
-
-  G_ResetRewindCountdown();
+  // This is called before the countdown decrement in `G_Ticker()`,
+  // so add 1 to keep it aligned
+  G_SetRewindCountdown((rewind_interval * TICRATE) + 1);
 }
 
 void G_EnableRewind(void)
@@ -3102,10 +3118,8 @@ void G_Ticker(void)
       && gamestate == GS_LEVEL && oldleveltime < leveltime
       && players[consoleplayer].playerstate != PST_DEAD)
   {
-    if (!rewind_countdown)
+    if (--rewind_countdown <= 0)
     { G_SaveKeyFrame(); }
-    else
-    { rewind_countdown--; }
   }
   else if (!CASUALPLAY(rewind_depth) || gamestate != GS_LEVEL)
   {

src/g_game.h

@@ -114,7 +114,7 @@ extern int cpars[];     // hardcoded array size
 
 // [Nugget] Rewind -----------------------------------------------------------
 
-extern void G_ResetRewindCountdown(void);
+extern void G_SetRewindCountdown(int value);
 extern void G_EnableRewind(void);
 extern void G_Rewind(void);
 extern void G_ClearExcessKeyFrames(void);

src/mn_setup.c

@@ -2733,7 +2733,7 @@ setup_menu_t gen_settings8[] = {
 static void UpdateRewindInterval(void)
 {
   G_EnableRewind();
-  G_ResetRewindCountdown();
+  G_SetRewindCountdown((rewind_interval * TICRATE) - ((leveltime - 1) % (rewind_interval * TICRATE)));
 }
 
 static void UpdateRewindDepth(void)