Codechange: Cache layouted text for the last used width. (#14177)

src/gfx_layout.cpp

@@ -174,11 +174,21 @@ Layouter::Layouter(std::string_view str, int maxw, FontSize fontsize) : string(s
 			}
 		}
 
-		/* Move all lines into a local cache so we can reuse them later on more easily. */
+		if (line.cached_width != maxw) {
-		for (;;) {
+			/* First run or width has changed, so we need to go through the layouter. Lines are moved into a cache to
-			auto l = line.layout->NextLine(maxw);
+			 * be reused if the width is not changed. */
-			if (l == nullptr) break;
+			line.cached_layout.clear();
-			this->push_back(std::move(l));
+			line.cached_width = maxw;
+			for (;;) {
+				auto l = line.layout->NextLine(maxw);
+				if (l == nullptr) break;
+				line.cached_layout.push_back(std::move(l));
+			}
+		}
+
+		/* Retrieve layout from the cache. */
+		for (const auto &l : line.cached_layout) {
+			this->push_back(l.get());
 		}
 
 		/* Break out if this was the last line. */

src/gfx_layout.h

@@ -135,7 +135,7 @@ public:
  *
  * It also accounts for the memory allocations and frees.
  */
-class Layouter : public std::vector<std::unique_ptr<const ParagraphLayouter::Line>> {
+class Layouter : public std::vector<const ParagraphLayouter::Line *> {
 	std::string_view string; ///< Pointer to the original string.
 
 	/** Key into the linecache */
@@ -174,6 +174,9 @@ public:
 
 		FontState state_after;     ///< Font state after the line.
 		std::unique_ptr<ParagraphLayouter> layout = nullptr; ///< Layout of the line.
+
+		std::vector<std::unique_ptr<const ParagraphLayouter::Line>> cached_layout{}; ///< Cached results of line layouting.
+		int cached_width = 0; ///< Width used for the cached layout.
 	};
 private:
 	typedef std::map<LineCacheKey, LineCacheItem, LineCacheCompare> LineCache;