Fix #527: Shift+click extends the text selection (#560)

A plain click on a page cleared the text selection whatever modifiers were
held, so there was no way to extend a selection with Shift+click as in
Acrobat. Now, when Shift is held and there is a text selection on the
clicked page, the click moves the selection head to the nearest text
position and keeps the anchor. Without Shift, or with no selection on that
page, a click still clears the selection. Selections remain single-page:
cross-page selection (the issue's second request) is not part of this
change.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/canvas.rs

@@ -1758,7 +1758,14 @@ pub fn document_area(app: &mut PdfCraftApp, index: usize, ui: &mut egui::Ui) {
                             view.selection = Some(Selection { page: i, anchor: first, head: last });
                         }
                     } else if resp.clicked() && !over_link {
-                        view.selection = None;
+                        // ⇧-click extends a selection on this page to the click, keeping its
+                        // anchor (#527). Otherwise (no shift, or no selection on this page; a
+                        // selection cannot yet span pages) a click clears the selection.
+                        let shift = ui.input(|inp| inp.modifiers.shift);
+                        match (view.selection.as_mut().filter(|s| shift && s.page == i), text.nearest(vx, vy)) {
+                            (Some(sel), Some(h)) => sel.head = h,
+                            _ => view.selection = None,
+                        }
                     }
                 }
             }

crates/ui-egui/tests/text_select.rs

@@ -85,3 +85,57 @@ fn quick_clicks_with_the_highlighter_mark_only_the_word() {
     assert_eq!(marks, [("Highlight", 1)], "one highlight, on the double-clicked word");
     assert!(app.views[0].selected_text().is_none());
 }
+
+/// Press at `from`, move to `to` and release there.
+fn drag(h: &mut Harness<'static, PdfCraftApp>, from: Pos2, to: Pos2) {
+    h.event(Event::PointerButton { pos: from, button: PointerButton::Primary, pressed: true, modifiers: Modifiers::NONE });
+    h.run_steps(1);
+    for k in 1..=4 {
+        h.hover_at(from + (to - from) * (k as f32 / 4.0));
+        h.run_steps(1);
+    }
+    h.event(Event::PointerButton { pos: to, button: PointerButton::Primary, pressed: false, modifiers: Modifiers::NONE });
+    h.run_steps(1);
+}
+
+/// Click at `pos` with Shift held.
+fn shift_click(h: &mut Harness<'static, PdfCraftApp>, pos: Pos2) {
+    h.event(Event::ModifiersChanged(Modifiers::SHIFT));
+    h.hover_at(pos);
+    h.run_steps(1);
+    for pressed in [true, false] {
+        h.event(Event::PointerButton { pos, button: PointerButton::Primary, pressed, modifiers: Modifiers::SHIFT });
+    }
+    h.run_steps(1);
+    h.event(Event::ModifiersChanged(Modifiers::NONE));
+    h.run_steps(1);
+}
+
+/// Issue #527: ⇧-click extends the text selection to the click, keeping its anchor.
+#[test]
+fn shift_click_extends_the_selection_from_its_anchor() {
+    let (mut h, _) = harness(|_| {});
+    let glyph = |h: &Harness<'static, PdfCraftApp>, g: usize| h.state().views[0].glyph_screen_pos(0, g).expect("glyph on screen");
+    // Drag over "quick" (glyphs 4..=8).
+    let (q, k) = (glyph(&h, 4), glyph(&h, 8));
+    drag(&mut h, q, k);
+    assert_eq!(h.state().views[0].selected_text().as_deref(), Some("quick"));
+    h.run_steps(60);
+    // ⇧-click on the "n" of "brown": the selection runs from the anchor to it.
+    let n = glyph(&h, 14);
+    shift_click(&mut h, n);
+    assert_eq!(h.state().views[0].selected_text().as_deref(), Some("quick brown"));
+    h.run_steps(60);
+    // ⇧-click before the anchor: the anchor stays, the selection now runs back to the click.
+    let t = glyph(&h, 0);
+    shift_click(&mut h, t);
+    assert_eq!(h.state().views[0].selected_text().as_deref(), Some("The q"));
+    h.run_steps(60);
+    // A plain click still clears it.
+    click(&mut h, n);
+    assert_eq!(h.state().views[0].selected_text(), None);
+    h.run_steps(60);
+    // ⇧-click with nothing selected selects nothing.
+    shift_click(&mut h, n);
+    assert_eq!(h.state().views[0].selected_text(), None);
+}

parity/acrobat-features.toml

@@ -1478,8 +1478,8 @@ milestone = "M3"
 status = "shipped"
 commands = []
 tools = []
-evidence = ["crates/ui-egui/tests/ui.rs::drag_selects_text_and_copy_returns_it", "crates/ui-egui/tests/ui.rs::selection_works_in_every_view_rotation", "crates/ui-egui/tests/text_select.rs::quick_clicks_select_a_word_then_the_line_then_the_page", "crates/ui-egui/tests/text_select.rs::quick_clicks_with_the_highlighter_mark_only_the_word"]
-notes = "Drag to select; with the Select tool, quick clicks select a word (two), the line (three) or all the text on the page (four). The markup and Redact tools mark a double-clicked word and stop there. Missing: paragraph selection, and ⌘A across the whole document (it selects the current page)."
+evidence = ["crates/ui-egui/tests/ui.rs::drag_selects_text_and_copy_returns_it", "crates/ui-egui/tests/ui.rs::selection_works_in_every_view_rotation", "crates/ui-egui/tests/text_select.rs::quick_clicks_select_a_word_then_the_line_then_the_page", "crates/ui-egui/tests/text_select.rs::quick_clicks_with_the_highlighter_mark_only_the_word", "crates/ui-egui/tests/text_select.rs::shift_click_extends_the_selection_from_its_anchor"]
+notes = "Drag to select; ⇧-click extends the selection to the click, keeping its anchor (same page only); with the Select tool, quick clicks select a word (two), the line (three) or all the text on the page (four). The markup and Redact tools mark a double-clicked word and stop there. Missing: selection across pages (dragging or ⇧-clicking onto another page), paragraph selection, and ⌘A across the whole document (it selects the current page)."
 
 [[feature]]
 id = "view.copy-text"