3 files changed, 55 insertions, 34 deletions

diff --git a/src/gfxinit.cpp b/src/gfxinit.cpp
index b744eaa5e..c0ba4c4d4 100644
--- a/src/gfxinit.cpp
+++ b/src/gfxinit.cpp
@@ -244,6 +244,28 @@ static void LoadSpriteTables()
 }
 
 
+static void RealChangeBlitter(const char *repl_blitter)
+{
+	const char *cur_blitter = BlitterFactory::GetCurrentBlitter()->GetName();
+	if (strcmp(cur_blitter, repl_blitter) == 0) return;
+
+	DEBUG(driver, 1, "Switching blitter from '%s' to '%s'... ", cur_blitter, repl_blitter);
+	Blitter *new_blitter = BlitterFactory::SelectBlitter(repl_blitter);
+	if (new_blitter == nullptr) NOT_REACHED();
+	DEBUG(driver, 1, "Successfully switched to %s.", repl_blitter);
+
+	if (!VideoDriver::GetInstance()->AfterBlitterChange()) {
+		/* Failed to switch blitter, let's hope we can return to the old one. */
+		if (BlitterFactory::SelectBlitter(cur_blitter) == nullptr || !VideoDriver::GetInstance()->AfterBlitterChange()) usererror("Failed to reinitialize video driver. Specify a fixed blitter in the config");
+	}
+
+	/* Clear caches that might have sprites for another blitter. */
+	VideoDriver::GetInstance()->ClearSystemSprites();
+	ClearFontCache();
+	GfxClearSpriteCache();
+	ReInitAllWindows(false);
+}
+
 /**
  * Check blitter needed by NewGRF config and switch if needed.
  * @return False when nothing changed, true otherwise.
@@ -309,7 +331,7 @@ static bool SwitchNewGRFBlitter()
 		if (BlitterFactory::GetBlitterFactory(repl_blitter) == nullptr) continue;
 
 		/* Inform the video driver we want to switch blitter as soon as possible. */
-		VideoDriver::GetInstance()->ChangeBlitter(repl_blitter);
+		VideoDriver::GetInstance()->QueueOnMainThread(std::bind(&RealChangeBlitter, repl_blitter));
 		break;
 	}
 
diff --git a/src/video/video_driver.cpp b/src/video/video_driver.cpp
index d8fbe0400..2f8efc4ad 100644
--- a/src/video/video_driver.cpp
+++ b/src/video/video_driver.cpp
@@ -97,27 +97,6 @@ void VideoDriver::StopGameThread()
 	this->game_thread.join();
 }
 
-void VideoDriver::RealChangeBlitter(const char *repl_blitter)
-{
-	const char *cur_blitter = BlitterFactory::GetCurrentBlitter()->GetName();
-
-	DEBUG(driver, 1, "Switching blitter from '%s' to '%s'... ", cur_blitter, repl_blitter);
-	Blitter *new_blitter = BlitterFactory::SelectBlitter(repl_blitter);
-	if (new_blitter == nullptr) NOT_REACHED();
-	DEBUG(driver, 1, "Successfully switched to %s.", repl_blitter);
-
-	if (!this->AfterBlitterChange()) {
-		/* Failed to switch blitter, let's hope we can return to the old one. */
-		if (BlitterFactory::SelectBlitter(cur_blitter) == nullptr || !this->AfterBlitterChange()) usererror("Failed to reinitialize video driver. Specify a fixed blitter in the config");
-	}
-
-	/* Clear caches that might have sprites for another blitter. */
-	this->ClearSystemSprites();
-	ClearFontCache();
-	GfxClearSpriteCache();
-	ReInitAllWindows(false);
-}
-
 void VideoDriver::Tick()
 {
 	if (!this->is_game_threaded && std::chrono::steady_clock::now() >= this->next_game_tick) {
@@ -159,10 +138,7 @@ void VideoDriver::Tick()
 
 			this->LockVideoBuffer();
 
-			if (this->change_blitter != nullptr) {
-				this->RealChangeBlitter(this->change_blitter);
-				this->change_blitter = nullptr;
-			}
+			this->DrainCommandQueue();
 
 			while (this->PollEvent()) {}
 			::InputLoop();
diff --git a/src/video/video_driver.hpp b/src/video/video_driver.hpp
index 4964e01cb..db522a761 100644
--- a/src/video/video_driver.hpp
+++ b/src/video/video_driver.hpp
@@ -22,6 +22,7 @@
 #include <mutex>
 #include <thread>
 #include <vector>
+#include <functional>
 
 extern std::string _ini_videodriver;
 extern std::vector<Dimension> _resolutions;
@@ -36,7 +37,7 @@ class VideoDriver : public Driver {
 	const uint DEFAULT_WINDOW_HEIGHT = 480u; ///< Default window height.
 
 public:
-	VideoDriver() : fast_forward_key_pressed(false), fast_forward_via_key(false), is_game_threaded(true), change_blitter(nullptr) {}
+	VideoDriver() : fast_forward_key_pressed(false), fast_forward_via_key(false), is_game_threaded(true) {}
 
 	/**
 	 * Mark a particular area dirty.
@@ -178,12 +179,16 @@ public:
 	}
 
 	/**
-	 * Queue a request to change the blitter. This is not executed immediately,
-	 * but instead on the next draw-tick.
+	 * Queue a function to be called on the main thread with game state
+	 * lock held and video buffer locked. Queued functions will be
+	 * executed on the next draw tick.
+	 * @param func Function to call.
 	 */
-	void ChangeBlitter(const char *new_blitter)
+	void QueueOnMainThread(std::function<void()> &&func)
 	{
-		this->change_blitter = new_blitter;
+		std::lock_guard<std::mutex> lock(this->cmd_queue_mutex);
+
+		this->cmd_queue.emplace_back(std::forward<std::function<void()>>(func));
 	}
 
 	void GameLoopPause();
@@ -328,11 +333,29 @@ protected:
 	static void GameThreadThunk(VideoDriver *drv);
 
 private:
+	std::mutex cmd_queue_mutex;
+	std::vector<std::function<void()>> cmd_queue;
+
+	/** Execute all queued commands. */
+	void DrainCommandQueue()
+	{
+		std::vector<std::function<void()>> cmds{};
+
+		{
+			/* Exchange queue with an empty one to limit the time we
+			 * hold the mutex. This also ensures that queued functions can
+			 * add new functions to the queue without everything blocking. */
+			std::lock_guard<std::mutex> lock(this->cmd_queue_mutex);
+			cmds.swap(this->cmd_queue);
+		}
+
+		for (auto &f : cmds) {
+			f();
+		}
+	}
+
 	void GameLoop();
 	void GameThread();
-	void RealChangeBlitter(const char *repl_blitter);
-
-	const char *change_blitter; ///< Request to change the blitter. nullptr if no pending request.
 };
 
 #endif /* VIDEO_VIDEO_DRIVER_HPP */