diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index ec39222a4..8ecaf9ac2 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -46,7 +46,7 @@ use lightcraft_catalog::{Catalog, Filter, Op, PhotoId, Sort};
 use lightcraft_develop::DevelopSettings;
 pub use media::{RenderJob, SourceLevel};
 use serde_json::Value;
-pub use view::{Browse, FilterChip, LibrarySource, Selection, filter_chips};
+pub use view::{Browse, FilterChip, LibrarySource, Selection, SelectionState, filter_chips};
 pub use {lightcraft_catalog as catalog, lightcraft_develop as develop, lightcraft_gpu as gpu, lightcraft_pipeline as pipeline};
 
 #[derive(Debug, thiserror::Error)]
diff --git a/crates/engine/src/view.rs b/crates/engine/src/view.rs
index 757adfe94..49d7462b3 100644
--- a/crates/engine/src/view.rs
+++ b/crates/engine/src/view.rs
@@ -74,7 +74,27 @@ pub struct Selection {
     pub active: Option<PhotoId>,
 }
 
+/// How a photo relates to the selection: what every view draws (grid cell, filmstrip cell…).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum SelectionState {
+    NotSelected,
+    /// Selected, but not the photo the loupe and panels act on.
+    Selected,
+    /// The most-selected photo.
+    Active,
+}
+
 impl Selection {
+    /// What views draw for `id`: active, selected or neither (one answer for grid, filmstrip, …).
+    pub fn state_of(&self, id: PhotoId) -> SelectionState {
+        if self.active == Some(id) {
+            SelectionState::Active
+        } else if self.contains(id) {
+            SelectionState::Selected
+        } else {
+            SelectionState::NotSelected
+        }
+    }
     pub fn single(id: PhotoId) -> Selection {
         Selection { ids: vec![id], active: Some(id) }
     }
@@ -203,3 +223,18 @@ fn date_label(d: &str) -> String {
         _ => d.to_string(),
     }
 }
+
+#[cfg(test)]
+mod selection_state_tests {
+    use super::*;
+    use lightcraft_catalog::PhotoId;
+
+    #[test]
+    fn select_all_marks_the_others_selected_and_one_active() {
+        let ids: Vec<PhotoId> = (1..=3).map(PhotoId).collect();
+        let s = Selection { ids: ids.clone(), active: Some(ids[0]) };
+        assert_eq!(s.state_of(ids[0]), SelectionState::Active);
+        assert_eq!(s.state_of(ids[1]), SelectionState::Selected);
+        assert_eq!(s.state_of(PhotoId(9)), SelectionState::NotSelected);
+    }
+}