Text selection: a drag after a double- or triple-click extends by whole words or lines (fixes #1685) (#1689)

Co-authored-by: Brandon Thomas <echelon@gmail.com>

crates/ui-egui/src/canvas.rs

@@ -266,6 +266,16 @@ impl Selection {
     }
 }
 
+/// The glyphs `clicks` quick clicks select around glyph `a`: two the word, three the line, more
+/// the page.
+fn click_unit(text: &PageText, clicks: u32, a: usize) -> Option<(usize, usize)> {
+    match clicks {
+        2 => text.word_at(a),
+        3 => text.line_at(a),
+        _ => text.glyphs.len().checked_sub(1).map(|last| (0, last)),
+    }
+}
+
 struct PageTex {
     tag: u64,
     tex: TextureHandle,
@@ -2840,11 +2850,7 @@ pub fn document_area(app: &mut PdfCraftApp, index: usize, ui: &mut egui::Ui) {
                         // Multi-click highlights immediately on pointer press instead of release (#1024).
                         let clicks = if view.clicks > 2 && tool != QuickTool::Select { 1 } else { view.clicks };
                         if clicks >= 2 && over_text {
-                            let span = text.nearest(vx, vy).and_then(|a| match clicks {
-                                2 => text.word_at(a),
-                                3 => text.line_at(a),
-                                _ => text.glyphs.len().checked_sub(1).map(|last| (0, last)),
-                            });
+                            let span = text.nearest(vx, vy).and_then(|a| click_unit(&text, clicks, a));
                             if let Some((first, last)) = span {
                                 view.selection = Some(Selection::run(i, first, last));
                             }
@@ -2862,10 +2868,22 @@ pub fn document_area(app: &mut PdfCraftApp, index: usize, ui: &mut egui::Ui) {
                             };
                         }
                     }
+                    let clicks = if view.clicks > 2 && tool != QuickTool::Select { 1 } else { view.clicks };
                     if resp.dragged()
                         && let Some(sel) = view.selection.as_mut().filter(|s| s.page == i)
                     {
                         match &mut sel.span {
+                            // After a multi-click the drag extends by its unit (#1685), as in
+                            // Acrobat and browsers: whole words or lines, always keeping the one
+                            // clicked, which holds the anchor whichever way the drag went.
+                            Span::Run { anchor, head } if clicks >= 2 => {
+                                if let Some(h) = text.nearest(vx, vy)
+                                    && let Some((first, last)) = click_unit(&text, clicks, *anchor)
+                                {
+                                    let (to_first, to_last) = click_unit(&text, clicks, h).unwrap_or((h, h));
+                                    (*anchor, *head) = if to_first < first { (last, to_first) } else { (first, to_last.max(last)) };
+                                }
+                            }
                             Span::Run { head, .. } => {
                                 if let Some(h) = text.nearest(vx, vy) {
                                     *head = h;
@@ -2901,11 +2919,7 @@ pub fn document_area(app: &mut PdfCraftApp, index: usize, ui: &mut egui::Ui) {
                     // (a highlight made by the double-click left its word selected).
                     if release_clicks > 0 && clicks >= 2 && over_text {
                         if view.selection.is_none() {
-                            let span = text.nearest(vx, vy).and_then(|a| match clicks {
-                                2 => text.word_at(a),
-                                3 => text.line_at(a),
-                                _ => text.glyphs.len().checked_sub(1).map(|last| (0, last)),
-                            });
+                            let span = text.nearest(vx, vy).and_then(|a| click_unit(&text, clicks, a));
                             if let Some((first, last)) = span {
                                 view.selection = Some(Selection::run(i, first, last));
                             }

crates/ui-egui/tests/ui_group/text_select.rs

@@ -314,3 +314,38 @@ fn a_selection_drag_held_at_the_bottom_edge_scrolls_the_view() {
     h.run_steps(2);
     assert_eq!(h.state().views[0].selected_text(), Some(held), "releasing keeps the selection");
 }
+
+/// Click at `at`, then press there again and drag to `to` before releasing: a double-click drag.
+fn double_click_drag(h: &mut Harness<'static, PdfCraftApp>, at: Pos2, to: Pos2) {
+    click(h, at);
+    press_and_move(h, at, to);
+    h.event(Event::PointerButton { pos: to, button: PointerButton::Primary, pressed: false, modifiers: Modifiers::NONE });
+    h.run_steps(1);
+}
+
+/// Issue #1685: dragging after a double-click extends the selection a word at a time, and the
+/// double-clicked word stays selected whichever way the drag goes.
+#[test]
+fn a_double_click_drag_extends_by_whole_words_both_ways() {
+    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");
+    // "The quick brown fox": the "u" of "quick" is glyph 5, the "o" of "brown" glyph 12.
+    let (u, o) = (glyph(&h, 5), glyph(&h, 12));
+    double_click_drag(&mut h, u, o);
+    let right = h.state().views[0].selected_text();
+    h.run_steps(60);
+    double_click_drag(&mut h, o, u);
+    let left = h.state().views[0].selected_text();
+    assert_eq!([right.as_deref(), left.as_deref()], [Some("quick brown"); 2], "dragging right, then left");
+}
+
+/// Issue #1685: after a triple-click the drag extends a whole line at a time.
+#[test]
+fn a_triple_click_drag_extends_by_whole_lines() {
+    let (mut h, at) = harness(|_| {});
+    // A glyph inside "jumps over the dog", on the second line.
+    let below = h.state().views[0].glyph_screen_pos(0, 23).expect("glyph on screen");
+    click(&mut h, at);
+    double_click_drag(&mut h, at, below);
+    assert_eq!(h.state().views[0].selected_text().as_deref(), Some("The quick brown fox\njumps over the dog"));
+}