Stats backgrounds: fit the category instead of album-wide random

The filter mini-album pages all drew their blurred background from the whole
album, so a filter page's background did not relate to its category. Mirror the
main album instead:

- A filter gallery's background is now a random photo from THAT filter's own set
  (like the album preview pages pick a random album photo).
- A filter view page's background is the photo it shows (like the album view
  pages).
- The stats overview still uses a random album-wide photo.

Adds _stats_pick_background (random pick from a filter's photo list) and drops
the now-unused album-wide background preload from render_filter_pages.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 27 insertions, 5 deletions

diff --git a/src/lib/stats.source.sh b/src/lib/stats.source.sh
index afc2d3b..cda2b61 100644
--- a/src/lib/stats.source.sh
+++ b/src/lib/stats.source.sh
@@ -944,6 +944,26 @@ _stats_random_background() {
     printf '%s' "${STATS_BG_PHOTOS[index]}"
 }
 
+# Pick a seeded-random photo from a newline-separated list (a filter's own
+# photos) for a filter gallery's blurred background, so the background fits the
+# category. Empty when the list is empty.
+_stats_pick_background() {
+    local -r context="$1"; shift
+    local -r photos="$1"; shift
+    local -a list=()
+    local photo
+    local -i index
+
+    while IFS= read -r photo; do
+        [ -n "$photo" ] && list+=("$photo")
+    done <<< "$photos"
+    if (( ${#list[@]} == 0 )); then
+        return
+    fi
+    index=$(random_index "photo:filter:$context" "${#list[@]}")
+    printf '%s' "${list[index]}"
+}
+
 render_stats_page() {
     local -r html_dir="$1"; shift
     local -r backhref="$1"; shift
@@ -1051,7 +1071,10 @@ _stats_render_filter_gallery() {
 
     thumbs=$(_stats_build_filter_thumbs \
         "$backhref_html" "${STATS_FILTER_PHOTOS[$pagebase]}")
-    background_image=$(_stats_random_background "$pagebase/index")
+    # Background fits the category: a random photo from this filter's own set,
+    # mirroring how the album preview pages pick a random album photo.
+    background_image=$(_stats_pick_background \
+        "$pagebase" "${STATS_FILTER_PHOTOS[$pagebase]}")
     template header index.html \
         html_dir "$html_dir" backhref "$backhref" \
         blurs_dir "$STATS_BLURS_DIR" background_image "$background_image" \
@@ -1079,7 +1102,9 @@ _stats_render_filter_view_page() {
 
     body=$(_stats_build_filterview_body \
         "$STATS_FILTER_BACKHREF" "$photo" "$prev" "$next")
-    background_image=$(_stats_random_background "$pagebase/$index")
+    # The view page's blurred background is the photo it shows, exactly like the
+    # album view pages.
+    background_image="$photo"
     template header "$page" \
         html_dir "$html_dir" backhref "$backhref" \
         blurs_dir "$STATS_BLURS_DIR" background_image "$background_image" \
@@ -1211,9 +1236,6 @@ render_filter_pages() {
     if (( ${#STATS_FILTER_PHOTOS[@]} == 0 )); then
         return
     fi
-    # Load the background photo list once now so every forked render job inherits
-    # the cached array rather than rescanning the photos directory per page.
-    _stats_load_background_photos
     while IFS= read -r pagebase; do
         _stats_enqueue_filter_album "$pagebase" \
             render_job_pids render_job_statuses render_job_labels render_failed