From ff2309c1581c025ba8b9f65e6619fe2fe2252827 Mon Sep 17 00:00:00 2001
From: Lev Kropp <lev.kropp@canonical.com>
Date: Wed, 16 Oct 2024 13:17:09 -0400
Subject: [PATCH] Implement line-height snapping and full line rendering

---
 lib/src/ui/render.dart | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/lib/src/ui/render.dart b/lib/src/ui/render.dart
index de2a2f7..3ebaa59 100644
--- a/lib/src/ui/render.dart
+++ b/lib/src/ui/render.dart
@@ -154,7 +154,8 @@ class RenderTerminal extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
   var _stickToBottom = true;
 
   void _onScroll() {
-    _stickToBottom = _scrollOffset >= _maxScrollExtent;
+    final lineHeight = _painter.cellSize.height;
+    _stickToBottom = (_maxScrollExtent - _offset.pixels).abs() < lineHeight / 2;
     markNeedsLayout();
     _notifyEditableRect();
   }
@@ -209,12 +210,13 @@ class RenderTerminal extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
     size = constraints.biggest;
 
     _updateViewportSize();
-
     _updateScrollOffset();
 
     if (_stickToBottom) {
-      _offset.correctBy(_maxScrollExtent - _scrollOffset);
+      _offset.correctBy(_maxScrollExtent - _offset.pixels);
     }
+
+    _notifyEditableRect();
   }
 
   /// Total height of the terminal in pixels. Includes scrollback buffer.
@@ -224,8 +226,9 @@ class RenderTerminal extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
   /// The distance from the top of the terminal to the top of the viewport.
   // double get _scrollOffset => _offset.pixels;
   double get _scrollOffset {
-    // return _offset.pixels ~/ _painter.cellSize.height * _painter.cellSize.height;
-    return _offset.pixels;
+    final lineHeight = _painter.cellSize.height;
+    // Snap the scroll offset to the nearest multiple of lineHeight
+    return (_offset.pixels ~/ lineHeight) * lineHeight;
   }
 
   /// The height of a terminal line in pixels. This includes the line spacing.
@@ -373,7 +376,15 @@ class RenderTerminal extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
   }
 
   double get _maxScrollExtent {
-    return max(_terminalHeight - _viewportHeight, 0.0);
+    final totalLines = _terminal.buffer.lines.length;
+    final totalHeight = totalLines * _painter.cellSize.height;
+    final viewportHeight = _viewportHeight;
+    final maxExtent = totalHeight - viewportHeight;
+
+    final lineHeight = _painter.cellSize.height;
+    final adjustedMaxExtent = (maxExtent / lineHeight).ceil() * lineHeight;
+
+    return max(0.0, adjustedMaxExtent);
   }
 
   double get _lineOffset {
@@ -400,15 +411,14 @@ class RenderTerminal extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
 
   void _paint(PaintingContext context, Offset offset) {
     final canvas = context.canvas;
-
     final lines = _terminal.buffer.lines;
     final charHeight = _painter.cellSize.height;
 
     final firstLineOffset = _scrollOffset - _padding.top;
-    final lastLineOffset = _scrollOffset + size.height + _padding.bottom;
+    final lastLineOffset = _scrollOffset + size.height - _padding.bottom;
 
-    final firstLine = firstLineOffset ~/ charHeight;
-    final lastLine = lastLineOffset ~/ charHeight;
+    final firstLine = (firstLineOffset / charHeight).ceil();
+    final lastLine = (lastLineOffset / charHeight).floor() - 1;
 
     final effectFirstLine = firstLine.clamp(0, lines.length - 1);
     final effectLastLine = lastLine.clamp(0, lines.length - 1);