GUI2: When a label grows, attempt to only lay out the containing grid

This greatly improves responsiveness of the add-on manager (bug #25523).

changelog

@@ -1,4 +1,6 @@
 Version 1.13.7+dev:
+ * Performance:
+   * Greatly speeded up switching between add-ons in the add-on manager (bug #25523)
 
 Version 1.13.7:
  * AI:

src/gui/widgets/grid.cpp

@@ -20,6 +20,7 @@
 #include "gui/core/log.hpp"
 #include "gui/core/layout_exception.hpp"
 #include "gui/widgets/styled_widget.hpp"
+#include "gui/widgets/window.hpp"
 
 #include <numeric>
 
@@ -377,6 +378,43 @@ void grid::demand_reduce_height(const unsigned /*maximum_height*/)
 	/** @todo Implement. */
 }
 
+void grid::relayout()
+{
+	point size = get_size();
+	point best_size = calculate_best_size();
+	if(size.x >= best_size.x && size.y >= best_size.y) {
+		place(get_origin(), size);
+		return;
+	}
+
+	recalculate_best_size();
+
+	if(size.y >= best_size.y) {
+		// We have enough space in the Y direction, but not in the X direction.
+		// Try wrapping the content.
+		request_reduce_width(size.x);
+		best_size = get_best_size();
+
+		if(size.x >= best_size.x && size.y >= best_size.y) {
+			// Wrapping succeeded, we still fit vertically.
+			place(get_origin(), size);
+			return;
+		} else {
+			// Wrapping failed, we no longer fit.
+			// Reset the sizes of child widgets.
+			layout_initialise(true);
+		}
+	}
+
+	// Not enough space, ask the parent grid for more.
+	grid* parent = get_parent_grid();
+	if(parent != nullptr) {
+		parent->relayout();
+	} else {
+		get_window()->invalidate_layout();
+	}
+}
+
 point grid::recalculate_best_size()
 {
 	point best_size = calculate_best_size();

src/gui/widgets/grid.hpp

@@ -220,6 +220,13 @@ public:
 	/** See @ref widget::demand_reduce_height. */
 	virtual void demand_reduce_height(const unsigned maximum_height) override;
 
+	/**
+	 * Attempts to lay out the grid without laying out the entire window.
+	 * If the grid needs to grow, asks the parent grid for more space, recursively.
+	 * If the grid is the top-level grid, falls back to laying out the whole window.
+	 */
+	void relayout();
+
 	/**
 	 * Recalculates the best size.
 	 *

src/gui/widgets/scrollbar_container.cpp

@@ -582,10 +582,11 @@ bool scrollbar_container::content_resize_request(const bool force_sizing)
 				  == widget::visibility::invisible)) {
 
 			DBG_GUI_L << LOG_HEADER
-					  << " can't use horizontal scrollbar, ask window.\n";
-			window* window = get_window();
-			assert(window);
-			window->invalidate_layout();
+					  << " can't use horizontal scrollbar, ask grid.\n";
+			layout_initialise(true);
+			grid* grid = get_parent_grid();
+			assert(grid);
+			grid->relayout();
 			return false;
 		}
 	}
@@ -598,10 +599,11 @@ bool scrollbar_container::content_resize_request(const bool force_sizing)
 				  == widget::visibility::invisible)) {
 
 			DBG_GUI_L << LOG_HEADER
-					  << " can't use vertical scrollbar, ask window.\n";
-			window* window = get_window();
-			assert(window);
-			window->invalidate_layout();
+					  << " can't use vertical scrollbar, ask grid.\n";
+			layout_initialise(true);
+			grid* grid = get_parent_grid();
+			assert(grid);
+			grid->relayout();
 			return false;
 		}
 	}

src/gui/widgets/widget.cpp

@@ -14,6 +14,7 @@
 
 #define GETTEXT_DOMAIN "wesnoth-lib"
 
+#include "gui/widgets/grid.hpp"
 #include "gui/widgets/settings.hpp"
 #include "gui/widgets/window.hpp"
 #include "gui/core/event/message.hpp"
@@ -137,6 +138,16 @@ const window* widget::get_window() const
 	return dynamic_cast<const window*>(result);
 }
 
+grid* widget::get_parent_grid()
+{
+	widget* result = parent_;
+	while(result && dynamic_cast<grid*>(result) == nullptr) {
+		result = result->parent_;
+	}
+
+	return result ? dynamic_cast<grid*>(result) : nullptr;
+}
+
 dialogs::modal_dialog* widget::dialog()
 {
 	window* window = get_window();

src/gui/widgets/widget.hpp

@@ -32,6 +32,7 @@ namespace gui2
 struct builder_widget;
 namespace dialogs { class modal_dialog; }
 class window;
+class grid;
 
 namespace iteration
 {
@@ -176,10 +177,18 @@ public:
 	 * Get the parent window.
 	 *
 	 * @returns                   Pointer to parent window.
-	 * @retval nullptr               No parent window found.
+	 * @retval nullptr            No parent window found.
 	 */
 	window* get_window();
 
+	/**
+	 * Get the parent grid.
+	 *
+	 * @returns                 Pointer to parent grid.
+	 * @retval nullptr          No parent grid found.
+	 */
+	grid* get_parent_grid();
+
 	/** The constant version of @ref get_window. */
 	const window* get_window() const;