Fix text selection of centered and right-aligned text (#8076)

* Fixes https://github.com/emilk/egui/issues/8049
* Bug introduced in https://github.com/emilk/egui/pull/7831

crates/egui_demo_lib/src/demo/text_layout.rs

@@ -7,17 +7,21 @@ pub struct TextLayoutDemo {
     overflow_character: Option<char>,
     extra_letter_spacing: f32,
     line_height_pixels: u32,
+    halign: egui::Align,
+    justify: bool,
     lorem_ipsum: bool,
 }
 
 impl Default for TextLayoutDemo {
     fn default() -> Self {
         Self {
-            max_rows: 6,
-            break_anywhere: true,
+            max_rows: 1000,
+            break_anywhere: false,
             overflow_character: Some('…'),
             extra_letter_spacing: 0.0,
             line_height_pixels: 0,
+            halign: egui::Align::LEFT,
+            justify: false,
             lorem_ipsum: true,
         }
     }
@@ -48,6 +52,8 @@ impl crate::View for TextLayoutDemo {
             overflow_character,
             extra_letter_spacing,
             line_height_pixels,
+            halign,
+            justify,
             lorem_ipsum,
         } = self;
 
@@ -109,6 +115,18 @@ impl crate::View for TextLayoutDemo {
                 });
                 ui.end_row();
 
+                ui.label("Horizontal align:");
+                ui.horizontal(|ui| {
+                    ui.selectable_value(halign, egui::Align::LEFT, "Left");
+                    ui.selectable_value(halign, egui::Align::Center, "Center");
+                    ui.selectable_value(halign, egui::Align::RIGHT, "Right");
+                });
+                ui.end_row();
+
+                ui.label("Justify:");
+                ui.checkbox(justify, "Fill row width");
+                ui.end_row();
+
                 ui.label("Text:");
                 ui.horizontal(|ui| {
                     ui.selectable_value(lorem_ipsum, true, "Lorem Ipsum");
@@ -145,8 +163,14 @@ impl crate::View for TextLayoutDemo {
                     ..Default::default()
                 };
 
-                // NOTE: `Label` overrides some of the wrapping settings, e.g. wrap width
-                ui.label(job);
+                // NOTE: `Label` overrides some of the wrapping settings,
+                // e.g. wrap width, halign, and justify.
+                ui.with_layout(
+                    egui::Layout::top_down(*halign).with_cross_justify(*justify),
+                    |ui| {
+                        ui.label(job);
+                    },
+                );
             });
     }
 }

crates/egui_demo_lib/tests/misc.rs

@@ -62,21 +62,25 @@ fn test_italics() {
 fn test_text_selection() {
     let mut results = egui_kittest::SnapshotResults::new();
 
-    for (test_idx, drag_start_x) in [0.2_f32, 0.9].into_iter().enumerate() {
-        let mut harness = Harness::builder().build_ui(|ui| {
-            let visuals = ui.visuals_mut();
-            visuals.selection.bg_fill = Color32::LIGHT_GREEN;
-            visuals.selection.stroke.color = Color32::RED;
+    for (test_idx, drag_start_x) in [0.2_f32, 0.95].into_iter().enumerate() {
+        let mut harness = Harness::builder()
+            .with_pixels_per_point(1.0) // TODO(emilk): why does this test fail with 2.0?
+            .build_ui(|ui| {
+                let visuals = ui.visuals_mut();
+                visuals.selection.bg_fill = Color32::LIGHT_GREEN;
+                visuals.selection.stroke.color = Color32::RED;
 
-            ui.label("Some varied ☺ text :)\nAnd it has a second line!");
-        });
+                ui.vertical_centered(|ui| {
+                    ui.label("Some varied ☺ text :)\nAnd it has a second line!\nAnd a third!");
+                });
+            });
         harness.run();
         harness.fit_contents();
 
         // Drag to select text:
         let label = harness.get_by_role(Role::Label);
         harness.drag_at(label.rect().lerp_inside([drag_start_x, 0.25]));
-        harness.drop_at(label.rect().lerp_inside([0.6, 0.75]));
+        harness.drop_at(label.rect().lerp_inside([0.5, 0.75]));
         harness.run();
 
         harness.snapshot(format!("text_selection_{test_idx}"));

crates/egui_demo_lib/tests/snapshots/demos/Text Layout.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:4c47faa75a002577220a92efceab5c0ccee1ddaa17c2d2f3d6d1429dbf8fe718
-size 60887
+oid sha256:661570ed4bdf24d52ab049e7d3cf22ef4d50542ee5486d133e0a618a6146da42
+size 98582

crates/egui_demo_lib/tests/snapshots/text_selection_0.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:ce1e16fa09588ec5351d031408657137f42ff40eb7cf6dd00b8c65a4f51ec680
-size 5332
+oid sha256:d7d8578b55ed8fdaf2062cb53d7320555e490289ff9efb30f39ebb697d2e252e
+size 6529

crates/egui_demo_lib/tests/snapshots/text_selection_1.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:79676693e9f1804c7e0a32ffa9bec3bde281446ffc184b55a1a3fcf34074ac34
-size 5304
+oid sha256:5e09ec77bd473ad6695557b78d4967ade09b12100f04bc66d0e29779dfb0d551
+size 6495

crates/epaint/src/text/text_layout_types.rs

@@ -1047,7 +1047,7 @@ impl Galley {
             return self.end_pos();
         };
 
-        let x = row.x_offset(layout_cursor.column) + row.pos.x - self.rect.left();
+        let x = row.x_offset(layout_cursor.column) + row.pos.x;
         Rect::from_min_max(pos2(x, row.min_y()), pos2(x, row.max_y()))
     }
 
@@ -1092,7 +1092,7 @@ impl Galley {
             if is_pos_within_row || y_dist < best_y_dist {
                 best_y_dist = y_dist;
                 // char_at is `Row` not `PlacedRow` relative which means we have to subtract the pos.
-                let column = row.char_at(pos.x - row.pos.x + self.rect.left());
+                let column = row.char_at(pos.x - row.pos.x);
                 let prefer_next_row = column < row.char_count_excluding_newline();
                 cursor = CCursor {
                     index: ccursor_index + column,