Implement textual hit testing

native/src/widget/text.rs

@@ -1,7 +1,7 @@
 //! Write some text for your users to read.
 use crate::{
-    layout, Color, Element, Hasher, HorizontalAlignment, Layout, Length, Point,
-    Rectangle, Size, VerticalAlignment, Widget,
+    layout, Color, Element, Hasher, HitTestResult, HorizontalAlignment, Layout,
+    Length, Point, Rectangle, Size, VerticalAlignment, Widget,
 };
 
 use std::hash::Hash;
@@ -179,6 +179,23 @@ pub trait Renderer: crate::Renderer {
         bounds: Size,
     ) -> (f32, f32);
 
+    /// Tests whether the provided point is within the boundaries of [`Text`]
+    /// laid out with the given parameters, returning information about
+    /// the nearest character.
+    ///
+    /// If nearest_only is true, the hit test does not consider whether the
+    /// the point is interior to any glyph bounds, returning only the character
+    /// with the nearest centeroid.
+    fn hit_test(
+        &self,
+        contents: &str,
+        size: f32,
+        font: Self::Font,
+        bounds: Size,
+        point: Point,
+        nearest_only: bool,
+    ) -> HitTestResult;
+
     /// Draws a [`Text`] fragment.
     ///
     /// It receives:

native/src/widget/text_input.rs

@@ -707,15 +707,15 @@ pub trait Renderer: text::Renderer + Sized {
 
         let offset = self.offset(text_bounds, font, size, &value, &state);
 
-        find_cursor_position(
-            self,
-            &value,
+        self.hit_test(
+            &value.to_string(),
+            size.into(),
             font,
-            size,
-            x + offset,
-            0,
-            value.len(),
+            Size::INFINITY,
+            Point::new(x + offset, text_bounds.height / 2.0),
+            true,
         )
+        .cursor()
     }
 }
 
@@ -803,62 +803,6 @@ impl State {
     }
 }
 
-// TODO: Reduce allocations
-fn find_cursor_position<Renderer: self::Renderer>(
-    renderer: &Renderer,
-    value: &Value,
-    font: Renderer::Font,
-    size: u16,
-    target: f32,
-    start: usize,
-    end: usize,
-) -> usize {
-    if start >= end {
-        if start == 0 {
-            return 0;
-        }
-
-        let prev = value.until(start - 1);
-        let next = value.until(start);
-
-        let prev_width = renderer.measure_value(&prev.to_string(), size, font);
-        let next_width = renderer.measure_value(&next.to_string(), size, font);
-
-        if next_width - target > target - prev_width {
-            return start - 1;
-        } else {
-            return start;
-        }
-    }
-
-    let index = (end - start) / 2;
-    let subvalue = value.until(start + index);
-
-    let width = renderer.measure_value(&subvalue.to_string(), size, font);
-
-    if width > target {
-        find_cursor_position(
-            renderer,
-            value,
-            font,
-            size,
-            target,
-            start,
-            start + index,
-        )
-    } else {
-        find_cursor_position(
-            renderer,
-            value,
-            font,
-            size,
-            target,
-            start + index + 1,
-            end,
-        )
-    }
-}
-
 mod platform {
     use crate::keyboard;