Give a panorama a wide cell in the grid

A 4:1 composite drawn in one square cell is a strip a few pixels high.
A photograph about twice as wide as it is tall (1.9 and up) now spans
two columns, three from 2.9, with a thumbnail class of its own whose
long edge is sized for that width; on the tablet, or where the columns
are too few to put it beside anything, it takes the whole row.

Rows are computed in one place, library_ui::layout. The grid is a
lattice of slots: each cell is drawn at the slot Rust gives it, and a
wide cell that would not fit in what is left of a row starts the next
one, leaving the gap empty so the grid still reads in capture order.
The scrollbar spans the slots, a scroll reports a slot that the layout
turns back into an ordinal, and scrubs, restores and the cursor go
through the same conversion. Up and down step by rows through the
layout rather than by a row's worth of ordinals; left and right, a
shift-click's run, burst folding and the timeline are ordinal-based
and unchanged.

The window's own read carries each photograph's w and h, so the cells
know their shape with no query per cell. Where the wide ones sit in
the whole list is one query, run when what the grid lists changes or
when a window finds the layout out of date, and a library with no
panorama answers it from a partial index created on first use
(images_wide), not a schema bump. The merge makes the wide thumbnail
for a wide composite along with the others.

ui/dr-ui/src/library_ui/timeline.rs

@@ -18,7 +18,7 @@ use crate::{AppWindow, Library, TimelineBar, View};
 
 use super::controller::LibraryController;
 use super::filter_bar::{push_people_chips, refilter};
-use super::window::{load_window, mark_open, window_start};
+use super::window::{load_window, mark_open, seek_to, show_cursor, window_start};
 
 /// Move the timeline's zoom by whole levels.
 ///
@@ -501,13 +501,10 @@ fn scrub_to(window: &AppWindow, ctl: &Rc<LibraryController>, when: i64) {
     // Move the viewport as well as the window. Cells are drawn at their
     // absolute place in the library, so loading rows around image 15,000 while
     // the viewport sits at row 0 shows an empty grid until the user scrolls.
-    window
-        .global::<Library>()
-        .set_library_scroll_to(position as i32);
-    window
-        .global::<Library>()
-        .set_library_scroll_token(window.global::<Library>().get_library_scroll_token() + 1);
     load_window(window, ctl);
+    // After the load, which is what places the cells: the grid scrolls by
+    // slot, and a panorama before `position` moves its slot along.
+    seek_to(window, ctl, position);
 }
 
 /// TRACES: FR-CAT-7
@@ -543,12 +540,7 @@ pub fn restore_position(window: &AppWindow, ctl: &Rc<LibraryController>) {
     // `resume_at` is what the grid last reported as its first visible image,
     // which is the thing the photographer is actually looking at.
     let anchor = ctl.resume_at.get().min(total - 1);
-    window
-        .global::<Library>()
-        .set_library_scroll_to(anchor as i32);
-    window
-        .global::<Library>()
-        .set_library_scroll_token(window.global::<Library>().get_library_scroll_token() + 1);
+    seek_to(window, ctl, anchor);
 }
 
 /// Format a bucket start for the histogram's hover label.
@@ -998,16 +990,11 @@ pub(super) fn resume_position(
     // Before the grid is shown, not after: the markup gates it on an `if`, and
     // the rebuilt Flickable reads `scroll-to` in its `init`. Setting these
     // afterwards would leave that init to run against the previous position.
-    window
-        .global::<Library>()
-        .set_library_scroll_to(anchor as i32);
-    window
-        .global::<Library>()
-        .set_library_scroll_token(window.global::<Library>().get_library_scroll_token() + 1);
+    seek_to(window, ctl, anchor);
 
     if let Some(at) = focus {
         coll.set_cursor(Some(at));
-        window.global::<Library>().set_library_cursor(at as i32);
+        show_cursor(window, ctl, at);
     }
 
     // The view has moved, so the capture-time marker has to move with it.