From 01568acef2be24d7a7a5e8062307f30daa9a5014 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emilernerfeldt@gmail.com>
Date: Sat, 16 May 2020 20:54:01 +0200
Subject: [PATCH] TextEdit: click to move cursor

---
 emigui/src/font.rs              | 48 +++++++++++++++++++++++++++++++++
 emigui/src/widgets/text_edit.rs |  6 ++++-
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/emigui/src/font.rs b/emigui/src/font.rs
index 8999e8ad..4d8756be 100644
--- a/emigui/src/font.rs
+++ b/emigui/src/font.rs
@@ -39,6 +39,9 @@ pub struct Line {
     /// Bottom of the line, offset within the Galley.
     /// Unit: points.
     pub y_max: f32,
+
+    /// If true, the last char on this line is '\n'
+    pub ends_with_newline: bool,
 }
 
 impl Galley {
@@ -71,6 +74,31 @@ impl Galley {
             vec2(0.0, 0.0)
         }
     }
+
+    /// Character offset at the given position within the galley
+    pub fn char_at(&self, pos: Vec2) -> usize {
+        let mut best_y_dist = f32::INFINITY;
+        let mut char_idx = 0;
+
+        let mut char_count = 0;
+        for line in &self.lines {
+            let y_dist = (line.y_min - pos.y).abs().min((line.y_max - pos.y).abs());
+            if y_dist < best_y_dist {
+                best_y_dist = y_dist;
+                let line_offset = line.char_at(pos.x);
+                if line_offset == line.char_count() && line.ends_with_newline {
+                    // handle the case where line ends with a \n and we click after it.
+                    // We should return the position BEFORE the \n!
+                    char_idx = char_count + line_offset - 1;
+                } else {
+                    char_idx = char_count + line_offset;
+                }
+            }
+            char_count += line.char_count();
+        }
+        // eprintln!("char_at {:?}: {} (text: {:?})", pos, char_idx, self.text);
+        char_idx
+    }
 }
 
 impl Line {
@@ -90,6 +118,17 @@ impl Line {
     pub fn max_x(&self) -> f32 {
         *self.x_offsets.last().unwrap()
     }
+
+    /// Closest char at the desired x coordinate. return [0, char_count()]
+    pub fn char_at(&self, desired_x: f32) -> usize {
+        for (i, char_x_bounds) in self.x_offsets.windows(2).enumerate() {
+            let char_center_x = 0.5 * (char_x_bounds[0] + char_x_bounds[1]);
+            if desired_x < char_center_x {
+                return i;
+            }
+        }
+        self.char_count()
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -262,6 +301,7 @@ impl Font {
             x_offsets,
             y_min: 0.0,
             y_max: self.height(),
+            ends_with_newline: false,
         };
         let width = line.max_x();
         let size = vec2(width, self.height());
@@ -311,6 +351,7 @@ impl Font {
                 x_offsets: vec![0.0],
                 y_min: cursor_y,
                 y_max: cursor_y + line_spacing,
+                ends_with_newline: text.ends_with('\n'),
             });
         }
 
@@ -387,6 +428,7 @@ impl Font {
                                 .collect(),
                             y_min: cursor_y,
                             y_max: cursor_y + self.height(),
+                            ends_with_newline: false, // we'll fix this later
                         }
                     } else {
                         Line {
@@ -396,6 +438,7 @@ impl Font {
                                 .collect(),
                             y_min: cursor_y,
                             y_max: cursor_y + self.height(),
+                            ends_with_newline: false, // we'll fix this later
                         }
                     };
                     line.sanity_check();
@@ -423,11 +466,16 @@ impl Font {
                     .collect(),
                 y_min: cursor_y,
                 y_max: cursor_y + self.height(),
+                ends_with_newline: false, // we'll fix this later
             };
             line.sanity_check();
             out_lines.push(line);
         }
 
+        if text.ends_with('\n') {
+            out_lines.last_mut().unwrap().ends_with_newline = true;
+        }
+
         out_lines
     }
 }
diff --git a/emigui/src/widgets/text_edit.rs b/emigui/src/widgets/text_edit.rs
index 31e4feb5..0aaca9b6 100644
--- a/emigui/src/widgets/text_edit.rs
+++ b/emigui/src/widgets/text_edit.rs
@@ -2,7 +2,8 @@ use crate::*;
 
 #[derive(Clone, Copy, Debug, Default, serde_derive::Deserialize, serde_derive::Serialize)]
 pub(crate) struct State {
-    /// Charctaer based, NOT bytes
+    /// Charctaer based, NOT bytes.
+    /// TODO: store as line + row
     pub cursor: Option<usize>,
 }
 
@@ -62,6 +63,9 @@ impl<'t> Widget for TextEdit<'t> {
 
         if interact.clicked {
             ui.request_kb_focus(id);
+            if let Some(mouse_pos) = ui.input().mouse_pos {
+                state.cursor = Some(galley.char_at(mouse_pos - interact.rect.min));
+            }
         }
         if interact.hovered {
             ui.output().cursor_icon = CursorIcon::Text;