fix: select graphemes with multi codepoints properly

- We continue to use the graphemes index for the selection ends, however
  when calculating the selection rectangles we now check if the visual
  line had any glyph with `start` and `end` index bigger than 1 before
  or within the range and update the range accordingly. This way all the
  code that checks for word boundaries when selecting by words still
  functions properly.

1 files changed, 24 insertions, 14 deletions

diff --git a/src/text.rs b/src/text.rs
index ffd5ea2..9c132ad 100644
--- a/src/text.rs
+++ b/src/text.rs
@@ -830,7 +830,7 @@ fn highlight_line(
             .map(|glyph| glyph.end)
             .unwrap_or(0);
 
-        let range = start.max(from)..end.min(to);
+        let mut range = start.max(from)..end.min(to);
 
         let x_offset = visual_line
             .glyphs
@@ -843,21 +843,31 @@ fn highlight_line(
         } else if range.start == start && range.end == end {
             (x_offset, visual_line.w)
         } else {
-            let first_glyph = visual_line
-                .glyphs
-                .iter()
-                .position(|glyph| range.start <= glyph.start)
-                .unwrap_or(0);
-
-            let mut glyphs = visual_line.glyphs.iter();
+            let mut x = 0.0;
+            let mut width = 0.0;
+            for glyph in &visual_line.glyphs {
+                let glyph_count = glyph.start.abs_diff(glyph.end);
+
+                // Check for multi codepoint glyphs before or within the range
+                if glyph_count > 1 {
+                    if range.start > glyph.start {
+                        range.start += glyph_count - 1;
+                        range.end += glyph_count - 1;
+                    } else if range.end > glyph.start {
+                        range.end += glyph_count - 1;
+                    }
+                }
 
-            let x: f32 =
-                glyphs.by_ref().take(first_glyph).map(|glyph| glyph.w).sum();
+                if range.start > glyph.start {
+                    x += glyph.w;
+                }
 
-            let width: f32 = glyphs
-                .take_while(|glyph| range.end > glyph.start)
-                .map(|glyph| glyph.w)
-                .sum();
+                if range.start <= glyph.start && range.end > glyph.start {
+                    width += glyph.w;
+                } else if range.end <= glyph.start {
+                    break;
+                }
+            }
 
             (x_offset + x, width)
         }