Ensure that sprite aligner click to pick sprites is thread safe

Use a mutex for list of sprite IDs found in (threaded) draw jobs

src/gfx.cpp

@@ -1212,7 +1212,7 @@ static void GfxBlitter(const GfxBlitterCtx &ctx, const Sprite *sprite, int x, in
 		if (topleft <= clicked && clicked <= bottomright) {
 			uint offset = (((size_t)clicked - (size_t)topleft) / (blitter->GetScreenDepth() / 8)) % bp.pitch;
 			if (offset < (uint)bp.width) {
-				include(_newgrf_debug_sprite_picker.sprites, sprite_id);
+				_newgrf_debug_sprite_picker.FoundSpriteDuringDrawing(sprite_id);
 			}
 		}
 	}

src/newgrf_debug.h

@@ -24,9 +24,15 @@ enum NewGrfDebugSpritePickerMode {
 
 /** Spritepicker of SpriteAligner */
 struct NewGrfDebugSpritePicker {
-	NewGrfDebugSpritePickerMode mode;   ///< Current state
+	NewGrfDebugSpritePickerMode mode = SPM_NONE; ///< Current state
-	void *clicked_pixel;                ///< Clicked pixel (pointer to blitter buffer)
+	void *clicked_pixel = nullptr;               ///< Clicked pixel (pointer to blitter buffer)
 	std::vector<SpriteID> sprites;               ///< Sprites found
+
+	void DrawingComplete();
+	void FoundSpriteDuringDrawing(SpriteID sprite);
+
+private:
+	std::vector<SpriteID> draw_found_sprites;    ///< Sprites found (used from threaded drawing jobs, mutex must be held for all accesses)
 };
 
 extern NewGrfDebugSpritePicker _newgrf_debug_sprite_picker;

src/newgrf_debug_gui.cpp

@@ -11,6 +11,7 @@
 #include <stdarg.h>
 #include <functional>
 #include "core/backup_type.hpp"
+#include "core/container_func.hpp"
 #include "window_gui.h"
 #include "window_func.h"
 #include "random_access_file_type.h"
@@ -51,11 +52,27 @@
 #include "table/strings.h"
 
 #include <array>
+#include <mutex>
 
 #include "safeguards.h"
 
 /** The sprite picker. */
-NewGrfDebugSpritePicker _newgrf_debug_sprite_picker = { SPM_NONE, nullptr, std::vector<SpriteID>() };
+NewGrfDebugSpritePicker _newgrf_debug_sprite_picker;
+
+static std::mutex _newgrf_debug_sprite_picker_draw_mutex;
+
+void NewGrfDebugSpritePicker::DrawingComplete()
+{
+	std::lock_guard<std::mutex> lock(_newgrf_debug_sprite_picker_draw_mutex);
+	this->sprites.swap(this->draw_found_sprites);
+	this->draw_found_sprites.clear();
+}
+
+void NewGrfDebugSpritePicker::FoundSpriteDuringDrawing(SpriteID sprite)
+{
+	std::lock_guard<std::mutex> lock(_newgrf_debug_sprite_picker_draw_mutex);
+	include(this->draw_found_sprites, sprite);
+}
 
 /**
  * Get the feature index related to the window number.

src/window.cpp

@@ -3082,6 +3082,7 @@ void HandleMouseEvents()
 		/* We are done with the last draw-frame, so we know what sprites we
 		 * clicked on. Reset the picker mode and invalidate the window. */
 		_newgrf_debug_sprite_picker.mode = SPM_NONE;
+		_newgrf_debug_sprite_picker.DrawingComplete();
 		InvalidateWindowData(WC_SPRITE_ALIGNER, 0, 1);
 	}