Measure the line grid with the strut the lines are laid out with

example/pubspec.lock

@@ -13,18 +13,18 @@ packages:
     dependency: transitive
     description:
       name: characters
-      sha256: "04a925763edad70e8443c99234dc3328f442e811f1d8fd1a72f1c8ad0f69a605"
+      sha256: faf38497bda5ead2a8c7615f4f7939df04333478bf32e4173fcb06d428b5716b
       url: "https://pub.dev"
     source: hosted
-    version: "1.3.0"
+    version: "1.4.1"
   collection:
     dependency: "direct main"
     description:
       name: collection
-      sha256: ee67cb0715911d28db6bf4af1026078bd6f0128b07a5f66fb2ed94ec6783c09a
+      sha256: "2f5709ae4d3d59dd8f7cd309b4e023046b57d8a6c82130785d2b0e5868084e76"
       url: "https://pub.dev"
     source: hosted
-    version: "1.18.0"
+    version: "1.19.1"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -66,18 +66,18 @@ packages:
     dependency: transitive
     description:
       name: material_color_utilities
-      sha256: "0e0a020085b65b6083975e499759762399b4475f766c21668c4ecca34ea74e5a"
+      sha256: "9c337007e82b1889149c82ed242ed1cb24a66044e30979c44912381e9be4c48b"
       url: "https://pub.dev"
     source: hosted
-    version: "0.8.0"
+    version: "0.13.0"
   meta:
     dependency: transitive
     description:
       name: meta
-      sha256: d584fa6707a52763a52446f02cc621b077888fb63b93bbcb1143a7be5a0c0c04
+      sha256: "1741988757a65eb6b36abe716829688cf01910bbf91c34354ff7ec1c3de2b349"
       url: "https://pub.dev"
     source: hosted
-    version: "1.11.0"
+    version: "1.18.0"
   path:
     dependency: transitive
     description:
@@ -92,7 +92,7 @@ packages:
       path: ".."
       relative: true
     source: path
-    version: "0.9.0"
+    version: "0.10.0"
   re_highlight:
     dependency: "direct main"
     description:
@@ -105,7 +105,7 @@ packages:
     dependency: transitive
     description: flutter
     source: sdk
-    version: "0.0.99"
+    version: "0.0.0"
   stream_channel:
     dependency: transitive
     description:
@@ -118,10 +118,10 @@ packages:
     dependency: transitive
     description:
       name: vector_math
-      sha256: "80b3257d1492ce4d091729e3a67a60407d227c27241d6927be0130c98e741803"
+      sha256: d530bd74fea330e6e364cda7a85019c434070188383e1cd8d9777ee586914c5b
       url: "https://pub.dev"
     source: hosted
-    version: "2.1.4"
+    version: "2.2.0"
 sdks:
-  dart: ">=3.2.0-0 <4.0.0"
+  dart: ">=3.10.0-0 <4.0.0"
   flutter: ">=1.17.0"

lib/src/_code_field.dart

@@ -1183,8 +1183,23 @@ class _CodeFieldRender extends RenderBox implements MouseTrackerAnnotation {
   }
 
   void _calculatePreferredLineHeight() {
+    // Measured with the same strut the paragraphs are laid out with, see
+    // `_CodeParagraphProvider.updateBaseStyle`.
+    //
+    // This number is the grid the editor places lines on, so it has to be the
+    // height a line actually gets. Measured without the strut it was three
+    // points taller here, and every line scrolled past added that much to the
+    // correction the layout applies to the scroll offset. Scrolling up by a
+    // page then pushed the offset above the top of the document and the
+    // physics sprang it back — a bounce nobody asked for.
     final TextPainter painter = TextPainter(
       textDirection: TextDirection.ltr,
+      strutStyle: StrutStyle(
+        fontSize: _textStyle.fontSize,
+        fontFamily: _textStyle.fontFamily,
+        height: _textStyle.height,
+        forceStrutHeight: true,
+      ),
     );
     painter.text = TextSpan(
       text: '0',

lib/src/_code_paragraph.dart

@@ -128,7 +128,20 @@ class _ParagraphImpl extends IParagraph {
     if (range.isCollapsed) {
       return const [];
     }
-    return paragraph.getBoxesForRange(range.start, range.end, boxHeightStyle: ui.BoxHeightStyle.max).map((e) => e.toRect()).toList();
+    // Selection boxes span the whole line of the grid rather than the ascent
+    // and descent of the glyphs.
+    //
+    // `BoxHeightStyle.max` measures the runs, and a run is shorter than the
+    // line it sits on, so adjacent boxes did not touch and a selection dragged
+    // over several lines looked striped. An empty line made it obvious: the
+    // branch above returns a box of a full `preferredLineHeight` for it, so
+    // the gap changed depending on whether a line had any text on it.
+    return paragraph.getBoxesForRange(range.start, range.end, boxHeightStyle: ui.BoxHeightStyle.max).map((e) {
+      final Rect rect = e.toRect();
+      final int line = max(0, (rect.center.dy / _preferredLineHeight).floor());
+      final double top = line * _preferredLineHeight;
+      return Rect.fromLTRB(rect.left, top, rect.right, top + _preferredLineHeight);
+    }).toList();
   }
 
   Offset? _getOffsetDownstream(int position) {
@@ -210,19 +223,26 @@ class _CodeParagraphProvider {
     if (uiStyle == _style) {
       return;
     }
+    // One strut for both the paragraph layout and the line height measured
+    // below. Measured without the strut, `_preferredLineHeight` is a different
+    // number than the height a line is actually given: for Consolas 13.09 it
+    // is 21 against 18. Lines are then placed on a grid that is taller than
+    // they are, which shows up as a stripe of background between them.
+    final StrutStyle strutStyle = StrutStyle(
+      fontSize: style.fontSize,
+      fontFamily: style.fontFamily,
+      height: style.height,
+      forceStrutHeight: true,
+    );
     _paragraphStyle = style.getParagraphStyle(
       textAlign: TextAlign.left,
       textDirection: TextDirection.ltr,
-      strutStyle: StrutStyle(
-        fontSize: style.fontSize,
-        fontFamily: style.fontFamily,
-        height: style.height,
-        forceStrutHeight: true,
-      )
+      strutStyle: strutStyle
     );
     _style = uiStyle;
     final TextPainter painter = TextPainter(
       textDirection: TextDirection.ltr,
+      strutStyle: strutStyle,
     );
     painter.text = TextSpan(
       text: '0',