[gnome-software] gs-feature-tile: Only change CSS on GTK widget if metadata has changed

[Philip Withnall <pwithnall src gnome org>]

commit 5638bb1da2b716d1dd520f1f7c350db5d83667de
Author: Philip Withnall <withnall endlessm com>
Date:   Mon Jun 8 16:42:58 2020 +0100

    gs-feature-tile: Only change CSS on GTK widget if metadata has changed
    
    `refresh()` gets called more than once on each `GsFeatureTile` during
    startup of gnome-software, leading to multiple `GtkCssProvider`s being
    created and attached to each `GsFeatureTile`. For feature tiles which
    set an image background (most of them), this results in the background
    being loaded multiple times and kept around in memory.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>

 src/gs-feature-tile.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)
---
diff --git a/src/gs-feature-tile.c b/src/gs-feature-tile.c
index b932b1eb..150364f9 100644
--- a/src/gs-feature-tile.c
+++ b/src/gs-feature-tile.c
@@ -21,6 +21,7 @@ struct _GsFeatureTile
        GtkWidget       *stack;
        GtkWidget       *title;
        GtkWidget       *subtitle;
+       const gchar     *markup_cache;  /* (unowned) (nullable) */
 };
 
 G_DEFINE_TYPE (GsFeatureTile, gs_feature_tile, GS_TYPE_APP_TILE)
@@ -33,7 +34,6 @@ gs_feature_tile_refresh (GsAppTile *self)
        AtkObject *accessible;
        const gchar *markup;
        g_autofree gchar *name = NULL;
-       g_autoptr(GsCss) css = NULL;
 
        if (app == NULL)
                return;
@@ -44,17 +44,21 @@ gs_feature_tile_refresh (GsAppTile *self)
        gtk_label_set_label (GTK_LABEL (tile->title), gs_app_get_name (app));
        gtk_label_set_label (GTK_LABEL (tile->subtitle), gs_app_get_summary (app));
 
-       /* perhaps set custom css */
+       /* perhaps set custom css; cache it so that images don’t get reloaded
+        * unnecessarily */
        markup = gs_app_get_metadata_item (app, "GnomeSoftware::FeatureTile-css");
-       css = gs_css_new ();
-       if (markup != NULL)
-               gs_css_parse (css, markup, NULL);
-       gs_utils_widget_set_css (GTK_WIDGET (tile), "feature-tile",
-                                gs_css_get_markup_for_id (css, "tile"));
-       gs_utils_widget_set_css (tile->title, "feature-tile-name",
-                                gs_css_get_markup_for_id (css, "name"));
-       gs_utils_widget_set_css (tile->subtitle, "feature-tile-subtitle",
-                                gs_css_get_markup_for_id (css, "summary"));
+       if (tile->markup_cache != markup) {
+               g_autoptr(GsCss) css = gs_css_new ();
+               if (markup != NULL)
+                       gs_css_parse (css, markup, NULL);
+               gs_utils_widget_set_css (GTK_WIDGET (tile), "feature-tile",
+                                        gs_css_get_markup_for_id (css, "tile"));
+               gs_utils_widget_set_css (tile->title, "feature-tile-name",
+                                        gs_css_get_markup_for_id (css, "name"));
+               gs_utils_widget_set_css (tile->subtitle, "feature-tile-subtitle",
+                                        gs_css_get_markup_for_id (css, "summary"));
+               tile->markup_cache = markup;
+       }
 
        accessible = gtk_widget_get_accessible (GTK_WIDGET (tile));