Implement line numbers

src/line_number.rs

@@ -0,0 +1,49 @@
+use cosmic_text::{
+    Align, Attrs, AttrsList, BufferLine, Family, FontSystem, LayoutLine, ShapeBuffer, Shaping, Wrap,
+};
+use std::collections::HashMap;
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub struct LineNumberKey {
+    pub number: usize,
+    pub width: usize,
+}
+
+#[derive(Debug)]
+pub struct LineNumberCache {
+    cache: HashMap<LineNumberKey, Vec<LayoutLine>>,
+    scratch: ShapeBuffer,
+}
+
+impl LineNumberCache {
+    pub fn new() -> Self {
+        Self {
+            cache: HashMap::new(),
+            scratch: ShapeBuffer::default(),
+        }
+    }
+
+    pub fn clear(&mut self) {
+        self.cache.clear();
+    }
+
+    pub fn get(&mut self, font_system: &mut FontSystem, key: LineNumberKey) -> &Vec<LayoutLine> {
+        self.cache.entry(key).or_insert_with(|| {
+            //TODO: do not repeat, used in App::init
+            let attrs = Attrs::new().family(Family::Monospace);
+            let text = format!("{:width$}", key.number, width = key.width);
+            let mut buffer_line = BufferLine::new(text, AttrsList::new(attrs), Shaping::Advanced);
+            buffer_line.set_wrap(Wrap::None);
+            buffer_line.set_align(Some(Align::Left));
+            buffer_line
+                .layout_in_buffer(
+                    &mut self.scratch,
+                    font_system,
+                    1.0,    /* font size adjusted later */
+                    1000.0, /* dummy width */
+                    Wrap::None,
+                )
+                .to_vec()
+        })
+    }
+}