Implement vertical movement (for text editing)

Author: cmyr

CHANGELOG.md

@@ -46,6 +46,7 @@ You can find its changes [documented below](#060---2020-06-01).
 - 'Tabs' widget allowing static and dynamic tabbed layouts. ([#1160] by [@rjwittams])
 - `RichText` and `Attribute` types for creating rich text ([#1255] by [@cmyr])
 - `request_timer` can now be called from `LayoutCtx` ([#1278] by [@Majora320])
+- TextBox supports vertical movement ([#1280] by [@cmyr])
 
 ### Changed
 
@@ -490,6 +491,7 @@ Last release without a changelog :(
 [#1255]: https://github.com/linebender/druid/pull/1255
 [#1276]: https://github.com/linebender/druid/pull/1276
 [#1278]: https://github.com/linebender/druid/pull/1278
+[#1280]: https://github.com/linebender/druid/pull/1280
 
 [Unreleased]: https://github.com/linebender/druid/compare/v0.6.0...master
 [0.6.0]: https://github.com/linebender/druid/compare/v0.5.0...v0.6.0

druid/src/text/editor.rs

@@ -173,16 +173,18 @@ impl<T: TextStorage + EditableText> Editor<T> {
             EditAction::Delete => self.delete_forward(data),
             EditAction::JumpDelete(mvmt) | EditAction::JumpBackspace(mvmt) => {
                 let to_delete = if self.selection.is_caret() {
-                    movement(mvmt, self.selection, data, true)
+                    movement(mvmt, self.selection, &self.layout, true)
                 } else {
                     self.selection
                 };
                 data.edit(to_delete.range(), "");
                 self.selection = Selection::caret(to_delete.min());
             }
-            EditAction::Move(mvmt) => self.selection = movement(mvmt, self.selection, data, false),
+            EditAction::Move(mvmt) => {
+                self.selection = movement(mvmt, self.selection, &self.layout, false)
+            }
             EditAction::ModifySelection(mvmt) => {
-                self.selection = movement(mvmt, self.selection, data, true)
+                self.selection = movement(mvmt, self.selection, &self.layout, true)
             }
             EditAction::Click(action) => {
                 if action.mods.shift() {
@@ -240,7 +242,7 @@ impl<T: TextStorage + EditableText> Editor<T> {
 
     fn delete_forward(&mut self, data: &mut T) {
         let to_delete = if self.selection.is_caret() {
-            movement(Movement::Right, self.selection, data, true)
+            movement(Movement::Right, self.selection, &self.layout, true)
         } else {
             self.selection
         };

druid/src/text/layout.rs

@@ -174,6 +174,13 @@ impl<T: TextStorage> TextLayout<T> {
         self.text.as_ref()
     }
 
+    /// Returns the inner Piet [`TextLayout`] type.
+    ///
+    /// [`TextLayout`]: ./piet/trait.TextLayout.html
+    pub fn layout(&self) -> Option<&PietTextLayout> {
+        self.layout.as_ref()
+    }
+
     /// The size of the laid-out text.
     ///
     /// This is not meaningful until [`rebuild_if_needed`] has been called.

druid/src/text/movement.rs

@@ -14,7 +14,9 @@
 
 //! Text editing movements.
 
-use crate::text::{EditableText, Selection};
+use crate::kurbo::Point;
+use crate::piet::TextLayout as _;
+use crate::text::{EditableText, Selection, TextLayout, TextStorage};
 
 /// The specification of a movement.
 #[derive(Debug, PartialEq, Clone, Copy)]
@@ -23,6 +25,10 @@ pub enum Movement {
     Left,
     /// Move to the right by one grapheme cluster.
     Right,
+    /// Move up one visible line.
+    Up,
+    /// Move down one visible line.
+    Down,
     /// Move to the left by one word.
     LeftWord,
     /// Move to the right by one word.
@@ -37,44 +43,98 @@ pub enum Movement {
     EndOfDocument,
 }
 
-/// Compute the result of movement on a selection .
-pub fn movement(m: Movement, s: Selection, text: &impl EditableText, modify: bool) -> Selection {
-    let offset = match m {
+/// Compute the result of movement on a selection.
+///
+/// returns a new selection representing the state after the movement.
+///
+/// If `modify` is true, only the 'active' edge (the `end`) of the selection
+/// should be changed; this is the case when the user moves with the shift
+/// key pressed.
+pub fn movement<T: EditableText + TextStorage>(
+    m: Movement,
+    s: Selection,
+    layout: &TextLayout<T>,
+    modify: bool,
+) -> Selection {
+    let (text, layout) = match (layout.text(), layout.layout()) {
+        (Some(text), Some(layout)) => (text, layout),
+        _ => {
+            debug_assert!(false, "movement() called before layout rebuild");
+            return s;
+        }
+    };
+
+    let (offset, h_pos) = match m {
         Movement::Left => {
             if s.is_caret() || modify {
-                text.prev_grapheme_offset(s.end).unwrap_or(0)
+                text.prev_grapheme_offset(s.end)
+                    .map(|off| (off, None))
+                    .unwrap_or((0, s.h_pos))
             } else {
-                s.min()
+                (s.min(), None)
             }
         }
         Movement::Right => {
             if s.is_caret() || modify {
-                text.next_grapheme_offset(s.end).unwrap_or(s.end)
+                text.next_grapheme_offset(s.end)
+                    .map(|off| (off, None))
+                    .unwrap_or((s.end, s.h_pos))
             } else {
-                s.max()
+                (s.max(), None)
             }
         }
 
-        Movement::PrecedingLineBreak => text.preceding_line_break(s.end),
-        Movement::NextLineBreak => text.next_line_break(s.end),
+        Movement::Up => {
+            let cur_pos = layout.hit_test_text_position(s.end);
+            let h_pos = s.h_pos.unwrap_or(cur_pos.point.x);
+            if cur_pos.line == 0 {
+                (0, Some(h_pos))
+            } else {
+                let lm = layout.line_metric(cur_pos.line).unwrap();
+                let point_above = Point::new(h_pos, cur_pos.point.y - lm.height);
+                let up_pos = layout.hit_test_point(point_above);
+                (up_pos.idx, Some(point_above.x))
+            }
+        }
+        Movement::Down => {
+            let cur_pos = layout.hit_test_text_position(s.end);
+            let h_pos = s.h_pos.unwrap_or(cur_pos.point.x);
+            if cur_pos.line == layout.line_count() - 1 {
+                (text.len(), Some(h_pos))
+            } else {
+                let lm = layout.line_metric(cur_pos.line).unwrap();
+                // may not work correctly for point sizes below 1.0
+                let y_below = lm.y_offset + lm.height + 1.0;
+                let point_below = Point::new(h_pos, y_below);
+                let up_pos = layout.hit_test_point(point_below);
+                (up_pos.idx, Some(point_below.x))
+            }
+        }
 
-        Movement::StartOfDocument => 0,
-        Movement::EndOfDocument => text.len(),
+        Movement::PrecedingLineBreak => (text.preceding_line_break(s.end), None),
+        Movement::NextLineBreak => (text.next_line_break(s.end), None),
+
+        Movement::StartOfDocument => (0, None),
+        Movement::EndOfDocument => (text.len(), None),
 
         Movement::LeftWord => {
-            if s.is_caret() || modify {
+            let offset = if s.is_caret() || modify {
                 text.prev_word_offset(s.end).unwrap_or(0)
             } else {
                 s.min()
-            }
+            };
+            (offset, None)
         }
         Movement::RightWord => {
-            if s.is_caret() || modify {
+            let offset = if s.is_caret() || modify {
                 text.next_word_offset(s.end).unwrap_or(s.end)
             } else {
                 s.max()
-            }
+            };
+            (offset, None)
         }
     };
-    Selection::new(if modify { s.start } else { offset }, offset)
+
+    let start = if modify { s.start } else { offset };
+    Selection::new(start, offset).with_h_pos(h_pos)
 }

druid/src/text/selection.rs

@@ -28,13 +28,20 @@ pub struct Selection {
 
     /// The active edge of a selection, as a byte offset.
     pub end: usize,
+
+    /// The saved horizontal position, during vertical movement.
+    pub h_pos: Option<f64>,
 }
 
 impl Selection {
     /// Create a selection that begins at start and goes to end.
     /// Like dragging a mouse from start to end.
     pub fn new(start: usize, end: usize) -> Self {
-        Selection { start, end }
+        Selection {
+            start,
+            end,
+            h_pos: None,
+        }
     }
 
     /// Create a selection that starts at the beginning and ends at text length.
@@ -49,9 +56,16 @@ impl Selection {
         Selection {
             start: pos,
             end: pos,
+            h_pos: None,
         }
     }
 
+    /// Construct a new selection from this selection, with the provided h_pos.
+    pub fn with_h_pos(mut self, h_pos: Option<f64>) -> Self {
+        self.h_pos = h_pos;
+        self
+    }
+
     /// If start == end, it's a caret
     pub fn is_caret(self) -> bool {
         self.start == self.end

druid/src/text/text_input.rs

@@ -112,6 +112,18 @@ impl TextInput for BasicTextInput {
             k_e if (HotKey::new(None, KbKey::ArrowRight)).matches(k_e) => {
                 EditAction::Move(Movement::Right)
             }
+            k_e if (HotKey::new(None, KbKey::ArrowUp)).matches(k_e) => {
+                EditAction::Move(Movement::Up)
+            }
+            k_e if (HotKey::new(None, KbKey::ArrowDown)).matches(k_e) => {
+                EditAction::Move(Movement::Down)
+            }
+            k_e if (HotKey::new(SysMods::Shift, KbKey::ArrowUp)).matches(k_e) => {
+                EditAction::ModifySelection(Movement::Up)
+            }
+            k_e if (HotKey::new(SysMods::Shift, KbKey::ArrowDown)).matches(k_e) => {
+                EditAction::ModifySelection(Movement::Down)
+            }
             // Delete left word
             k_e if (HotKey::new(SysMods::Cmd, KbKey::Backspace)).matches(k_e) => {
                 EditAction::JumpBackspace(Movement::LeftWord)