Add get_rect_union() for future usage.

src/sdl_utils.cpp

@@ -83,6 +83,29 @@ SDL_Rect intersect_rects(SDL_Rect const &rect1, SDL_Rect const &rect2)
 	return res;
 }
 
+SDL_Rect get_rect_union(const SDL_Rect& rect1, const SDL_Rect& rect2)
+{
+	const int left_side = std::max(rect1.x, rect2.x);
+	const int right_side = std::min(rect1.x + rect1.w, rect2.x + rect2.w);
+	if(left_side > right_side) {
+		return empty_rect;
+	}
+
+	const int top_side = std::max(rect1.y, rect2.y);
+	const int bottom_side = std::min(rect1.y + rect1.h, rect2.y + rect2.h);
+	if(top_side > bottom_side) {
+		return empty_rect;
+	}
+
+	SDL_Rect result = {
+			left_side,
+			top_side,
+			right_side - left_side,
+			bottom_side - top_side};
+
+	return result;
+}
+
 SDL_Rect create_rect(const int x, const int y, const int w, const int h)
 {
 	SDL_Rect rect = { x, y, w, h };

src/sdl_utils.hpp

@@ -57,6 +57,16 @@ bool point_in_rect(int x, int y, const SDL_Rect& rect);
 bool rects_overlap(const SDL_Rect& rect1, const SDL_Rect& rect2);
 SDL_Rect intersect_rects(SDL_Rect const &rect1, SDL_Rect const &rect2);
 
+/**
+ * Returns the union of two rectangles.
+ *
+ * @param rect1                   The first rectangle.
+ * @param rect2                   The second rectangle.
+ *
+ * @returns                       The union of rect1 and rect2.
+ */
+SDL_Rect get_rect_union(const SDL_Rect& rect1, const SDL_Rect& rect2);
+
 /**
  *  Creates an empty SDL_Rect.
  *