Merge branch 'master' into jgrpp

# Conflicts:
#	.gitignore
#	CMakeLists.txt
#	src/3rdparty/optional/optional.hpp
#	src/group_cmd.cpp
#	src/industry_cmd.cpp
#	src/misc_gui.cpp
#	src/video/sdl2_v.cpp

src/gfx.cpp

@@ -2090,6 +2090,30 @@ void SetAnimatedMouseCursor(const AnimCursor *table)
 	SwitchAnimatedCursor();
 }
 
+/**
+ * Update cursor position on mouse movement for relative modes.
+ * @param delta_x How much change in the X position.
+ * @param delta_y How much change in the Y position.
+ */
+void CursorVars::UpdateCursorPositionRelative(int delta_x, int delta_y)
+{
+	if (this->fix_at) {
+		this->delta.x = delta_x;
+		this->delta.y = delta_y;
+	} else {
+		int last_position_x = this->pos.x;
+		int last_position_y = this->pos.y;
+
+		this->pos.x = Clamp(this->pos.x + delta_x, 0, _cur_resolution.width - 1);
+		this->pos.y = Clamp(this->pos.y + delta_y, 0, _cur_resolution.height - 1);
+
+		this->delta.x = last_position_x - this->pos.x;
+		this->delta.y = last_position_y - this->pos.y;
+
+		this->dirty = true;
+	}
+}
+
 /**
  * Update cursor position on mouse movement.
  * @param x New X position.