cache ProgressToNextGameTick and update it only once before rendering

Source/nthread.cpp

@@ -24,6 +24,7 @@ bool sgbThreadIsRunning;
 DWORD gdwLargestMsgSize;
 DWORD gdwNormalMsgSize;
 int last_tick;
+float gfProgressToNextGameTick = 0.0f;
 
 /* data */
 static SDL_Thread *sghThread = NULL;
@@ -242,21 +243,23 @@ bool nthread_has_500ms_passed()
 	return ticksElapsed >= 0;
 }
 
-float nthread_GetProgressToNextGameTick()
+void nthread_UpdateProgressToNextGameTick()
 {
 	if (!gbRunGame || PauseMode || (!gbIsMultiplayer && gmenu_is_active())) // if game is not running or paused there is no next gametick in the near future
-		return 0.0f;
+		return;
 	int currentTickCount = SDL_GetTicks();
 	int ticksElapsed = last_tick - currentTickCount;
-	if (ticksElapsed <= 0)
-		return 1.0f; // game tick is due
+	if (ticksElapsed <= 0) {
+		gfProgressToNextGameTick = 1.0f; // game tick is due
+		return;
+	}
 	int ticksAdvanced = gnTickDelay - ticksElapsed;
-	float percent = (float)ticksAdvanced / (float)gnTickDelay;
-	if (percent > 1.0f)
-		return 1.0f;
-	if (percent < 0.0f)
-		return 0.0f;
-	return percent;
+	float fraction = (float)ticksAdvanced / (float)gnTickDelay;
+	if (fraction > 1.0f)
+		gfProgressToNextGameTick = 1.0f;
+	if (fraction < 0.0f)
+		gfProgressToNextGameTick = 0.0f;
+	gfProgressToNextGameTick = fraction;
 }
 
 } // namespace devilution

Source/nthread.h

@@ -14,6 +14,7 @@ extern DWORD gdwTurnsInTransit;
 extern uintptr_t glpMsgTbl[MAX_PLRS];
 extern DWORD gdwLargestMsgSize;
 extern DWORD gdwNormalMsgSize;
+extern float gfProgressToNextGameTick; // the progress as a fraction (0.0f to 1.0f) in time to the next game tick
 
 void nthread_terminate_game(const char *pszFcn);
 DWORD nthread_send_and_recv_turn(DWORD cur_turn, int turn_delta);
@@ -27,6 +28,6 @@ bool nthread_has_500ms_passed();
  * @brief Calculates the progress in time to the next game tick
  * @return Progress as a fraction (0.0f to 1.0f)
  */
-float nthread_GetProgressToNextGameTick();
+void nthread_UpdateProgressToNextGameTick();
 
 }

Source/player.cpp

@@ -3681,7 +3681,7 @@ Sint32 GetFrameToUseForPlayerRendering(const PlayerStruct* pPlayer)
 	} else {
 		relevantAnimationLength = pPlayer->_pAnimLen;
 	}
-	float progressToNextGameTick = nthread_GetProgressToNextGameTick();
+	float progressToNextGameTick = gfProgressToNextGameTick;
 	float totalGameTicksForCurrentAnimationSequence = progressToNextGameTick + (float)pPlayer->_pAnimGameTicksSinceSequenceStarted; // we don't use the processed game ticks alone but also the fragtion of the next game tick (if a rendering happens between game ticks). This helps to smooth the animations.
 	int animationMaxGameTickets = relevantAnimationLength;
 	if (pPlayer->_pAnimDelay > 1)

Source/scrollrt.cpp

@@ -1533,6 +1533,8 @@ void DrawAndBlit()
 	lock_buf(0);
 	CelOutputBuffer out = GlobalBackBuffer();
 
+	nthread_UpdateProgressToNextGameTick();
+
 	DrawView(out, ViewX, ViewY);
 	if (ctrlPan) {
 		DrawCtrlPan(out);