From a34422dc2605165a1cdbd7063daa8f11772dd844 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=CE=B6eh=20Matt?= <m.moninger.h@gmail.com>
Date: Thu, 17 Jan 2019 23:22:27 +0100
Subject: [PATCH] Fix #8591: Game loop does not run at a consistent tick rate
 of 40 Hz (#8594)

* Fix #8591: Run game loop at consistent tick rate of 40hz.

* Update distribution/changelog.txt

Co-Authored-By: ZehMatt <m.moninger.h@gmail.com>
---
 distribution/changelog.txt       |  1 +
 src/openrct2/Context.cpp         | 14 ++++++++------
 src/openrct2/GameState.cpp       | 14 +++++++++-----
 src/openrct2/network/Network.cpp |  2 +-
 4 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index df2b294615..1ffb085974 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -53,6 +53,7 @@
 - Fix: [#8469] Crash modifying colour on hacked rides.
 - Fix: [#8508] Underground roto-drop is not going up.
 - Fix: [#8555] Multiplayer window text limits are not computed properly.
+- Fix: [#8591] Game loop does not run at a consistent tick rate of 40 Hz.
 - Improved: [#2940] Allow mouse-dragging to set patrol area (Singleplayer only).
 - Improved: [#7730] Draw extreme vertical and lateral Gs red in the ride window's graph tab.
 - Improved: [#7930] Automatically create folders for custom content.
diff --git a/src/openrct2/Context.cpp b/src/openrct2/Context.cpp
index 2bd2ea66a9..aa4c63d3c2 100644
--- a/src/openrct2/Context.cpp
+++ b/src/openrct2/Context.cpp
@@ -857,7 +857,7 @@ namespace OpenRCT2
 
             uint32_t elapsed = currentTick - _lastTick;
             _lastTick = currentTick;
-            _accumulator = std::min(_accumulator + elapsed, (uint32_t)GAME_UPDATE_MAX_THRESHOLD);
+            _accumulator = std::min(_accumulator + elapsed, static_cast<uint32_t>(GAME_UPDATE_MAX_THRESHOLD));
 
             _uiContext->ProcessMessages();
 
@@ -867,9 +867,12 @@ namespace OpenRCT2
                 return;
             }
 
-            _accumulator -= GAME_UPDATE_TIME_MS;
+            while (_accumulator >= GAME_UPDATE_TIME_MS)
+            {
+                Update();
+                _accumulator -= GAME_UPDATE_TIME_MS;
+            }
 
-            Update();
             if (!_isWindowMinimised && !gOpenRCT2Headless)
             {
                 _drawingEngine->BeginDraw();
@@ -884,7 +887,6 @@ namespace OpenRCT2
             uint32_t currentTick = platform_get_ticks();
 
             bool draw = !_isWindowMinimised && !gOpenRCT2Headless;
-
             if (_lastTick == 0)
             {
                 sprite_position_tween_reset();
@@ -894,7 +896,7 @@ namespace OpenRCT2
             uint32_t elapsed = currentTick - _lastTick;
 
             _lastTick = currentTick;
-            _accumulator = std::min(_accumulator + elapsed, (uint32_t)GAME_UPDATE_MAX_THRESHOLD);
+            _accumulator = std::min(_accumulator + elapsed, static_cast<uint32_t>(GAME_UPDATE_MAX_THRESHOLD));
 
             _uiContext->ProcessMessages();
 
@@ -915,7 +917,7 @@ namespace OpenRCT2
 
             if (draw)
             {
-                const float alpha = (float)_accumulator / GAME_UPDATE_TIME_MS;
+                const float alpha = std::min((float)_accumulator / GAME_UPDATE_TIME_MS, 1.0f);
                 sprite_position_tween_all(alpha);
 
                 _drawingEngine->BeginDraw();
diff --git a/src/openrct2/GameState.cpp b/src/openrct2/GameState.cpp
index b9be0b3eec..cb6de02a1e 100644
--- a/src/openrct2/GameState.cpp
+++ b/src/openrct2/GameState.cpp
@@ -73,11 +73,18 @@ void GameState::InitAll(int32_t mapSize)
     load_palette();
 }
 
+/**
+ * Function will be called every GAME_UPDATE_TIME_MS.
+ * It has its own loop which might run multiple updates per call such as
+ * when operating as a client it may run multiple updates to catch up with the server tick,
+ * another influence can be the game speed setting.
+ */
 void GameState::Update()
 {
     gInUpdateCode = true;
 
-    uint32_t numUpdates;
+    // Normal game play will update only once every GAME_UPDATE_TIME_MS
+    uint32_t numUpdates = 1;
 
     // 0x006E3AEC // screen_game_process_mouse_input();
     screenshot_check();
@@ -101,12 +108,9 @@ void GameState::Update()
     // Determine how many times we need to update the game
     if (gGameSpeed > 1)
     {
+        // Update more often if game speed is above normal.
         numUpdates = 1 << (gGameSpeed - 1);
     }
-    else
-    {
-        numUpdates = realtimeTicksElapsed;
-    }
 
     if (network_get_mode() == NETWORK_MODE_CLIENT && network_get_status() == NETWORK_STATUS_CONNECTED
         && network_get_authstatus() == NETWORK_AUTH_OK)
diff --git a/src/openrct2/network/Network.cpp b/src/openrct2/network/Network.cpp
index fc0d7ec66e..1d99495b65 100644
--- a/src/openrct2/network/Network.cpp
+++ b/src/openrct2/network/Network.cpp
@@ -30,7 +30,7 @@
 // This string specifies which version of network stream current build uses.
 // It is used for making sure only compatible builds get connected, even within
 // single OpenRCT2 version.
-#define NETWORK_STREAM_VERSION "21"
+#define NETWORK_STREAM_VERSION "22"
 #define NETWORK_STREAM_ID OPENRCT2_VERSION "-" NETWORK_STREAM_VERSION
 
 static rct_peep* _pickup_peep = nullptr;