diff --git a/src/render/context.rs b/src/render/context.rs
index 74eb7bb..d2864fd 100644
--- a/src/render/context.rs
+++ b/src/render/context.rs
@@ -43,11 +43,6 @@ impl Context {
         &self.state.font_desc
     }
 
-    #[inline]
-    pub fn ascent(&self) -> f64 {
-        self.state.cell_metrics.ascent
-    }
-
     #[inline]
     pub fn cell_metrics(&self) -> &CellMetrics {
         &self.state.cell_metrics
diff --git a/src/render/mod.rs b/src/render/mod.rs
index 21e6416..1b1797a 100644
--- a/src/render/mod.rs
+++ b/src/render/mod.rs
@@ -33,10 +33,10 @@ pub fn render(
         char_width,
         underline_position,
         underline_thickness,
+        ascent,
         ..
     } = font_ctx.cell_metrics();
     let mut line_y = 0.0;
-    let ascent = font_ctx.ascent();
     let (cursor_row, cursor_col) = ui_model.get_cursor();
 
     for (row, line) in ui_model.model().iter().enumerate() {
@@ -78,21 +78,20 @@ pub fn render(
 
             if cell.attrs.underline || cell.attrs.undercurl {
                 if cell.attrs.undercurl {
-                    // TODO: properly draw undercurl
+                    //FIXME: don't repaint all lines on changes
                     let sp = color_model.actual_cell_sp(cell);
                     ctx.set_source_rgba(sp.0, sp.1, sp.2, 0.7);
+
+                    let max_undercurl_height = (line_height - underline_position) * 2.0;
+                    let undercurl_height = (underline_thickness * 4.0).min(max_undercurl_height);
+                    let undercurl_y = line_y + underline_position - undercurl_height / 2.0;
+
                     ctx.show_error_underline(
                         line_x,
-                        line_y + underline_position,
+                        undercurl_y,
                         char_width,
-                        underline_thickness * 5.0,
+                        undercurl_height
                     );
-                //ctx.set_dash(&[4.0, 2.0], 0.0);
-                //ctx.set_line_width(underline_thickness);
-                //ctx.move_to(line_x, line_y + underline_position);
-                //ctx.line_to(line_x + char_width, line_y + underline_position);
-                //ctx.stroke();
-                //ctx.set_dash(&[], 0.0);
                 } else if cell.attrs.underline {
                     ctx.set_source_rgb(fg.0, fg.1, fg.2);
                     ctx.set_line_width(underline_thickness);
diff --git a/src/ui_model/line.rs b/src/ui_model/line.rs
index 3f2b449..587895c 100644
--- a/src/ui_model/line.rs
+++ b/src/ui_model/line.rs
@@ -158,10 +158,6 @@ impl Line {
         self.item_line[start_cell] = Some(Item::new(new_item.clone(), end_cell - start_cell + 1));
     }
 
-    pub fn mark_dirty_cell(&mut self, idx: usize) {
-        self.line[idx].dirty = true;
-    }
-
     pub fn get_item_mut(&mut self, cell_idx: usize) -> Option<&mut Item> {
         let item_idx = self.cell_to_item(cell_idx);
         if item_idx >= 0 {
diff --git a/src/ui_model/mod.rs b/src/ui_model/mod.rs
index 006f3bc..26e20d2 100644
--- a/src/ui_model/mod.rs
+++ b/src/ui_model/mod.rs
@@ -74,13 +74,13 @@ impl UiModel {
         let mut changed_region = self.cur_point();
         let line = &mut self.model[self.cur_row];
         line.dirty_line = true;
-        line.mark_dirty_cell(self.cur_col);
 
         let cell = &mut line[self.cur_col];
 
         cell.ch = text.chars().last().unwrap_or(' ');
         cell.attrs = attrs.map(Attrs::clone).unwrap_or_else(Attrs::new);
         cell.attrs.double_width = text.is_empty();
+        cell.dirty = true;
         self.cur_col += 1;
         if self.cur_col >= self.columns {
             self.cur_col -= 1;