Chart background on dark theme

lib/ui/chart_painter.dart

@@ -11,11 +11,15 @@ class ChartPainter extends CustomPainter {
     required this.channel,
     required this.session,
     required this.layout,
+    required this.isDark,
+    this.hoverLocalPos,
   });
 
   final int channel;
   final SessionController session;
   final LayoutController layout;
+  final bool isDark;
+  final Offset? hoverLocalPos;
 
   @override
   void paint(Canvas canvas, Size size) {
@@ -24,8 +28,19 @@ class ChartPainter extends CustomPainter {
     final plotH = size.height - padTop - padBottom;
     if (plotW <= 0 || plotH <= 0) return;
 
+    // Theme-dependent palette.
+    final bgColor = isDark ? const Color(0xFF1E1F22) : const Color(0xFFF7F7F4);
+    final lineColor =
+        isDark ? const Color(0xFF5EA8FF) : const Color(0xFF185FA5);
+    final hatchColor =
+        isDark ? const Color(0x66D17050) : const Color(0x55993C1D);
+    final markerColor =
+        isDark ? const Color(0xCCD17050) : const Color(0xAA993C1D);
+    final cursorColor =
+        isDark ? const Color(0xCCBBBBBB) : const Color(0xAA444444);
+
     // Background.
-    final bgPaint = Paint()..color = const Color(0xFFF7F7F4);
+    final bgPaint = Paint()..color = bgColor;
     canvas.drawRect(
       Rect.fromLTWH(padLeft, padTop, plotW, plotH),
       bgPaint,
@@ -86,7 +101,7 @@ class ChartPainter extends CustomPainter {
 
     // Hatched gap rectangles.
     final hatchPaint = Paint()
-      ..color = const Color(0x55993C1D)
+      ..color = hatchColor
       ..style = PaintingStyle.fill;
     for (final g in gaps.hatchedRanges) {
       final x0 = xForCol(g.startPx);
@@ -99,7 +114,7 @@ class ChartPainter extends CustomPainter {
 
     // Polyline.
     final linePaint = Paint()
-      ..color = const Color(0xFF185FA5)
+      ..color = lineColor
       ..strokeWidth = 1.2
       ..style = PaintingStyle.stroke;
     final path = Path();
@@ -132,7 +147,7 @@ class ChartPainter extends CustomPainter {
 
     // Sub-pixel marker lines.
     final markerPaint = Paint()
-      ..color = const Color(0xAA993C1D)
+      ..color = markerColor
       ..strokeWidth = 1;
     for (final px in gaps.markerPixels) {
       final x = xForCol(px);
@@ -143,8 +158,56 @@ class ChartPainter extends CustomPainter {
       );
     }
 
+    // Cursor crosshair + data dot (still inside the plot clip).
+    int? hoverCol;
+    double? hoverY;
+    int? hoverTsUs;
+    if (hoverLocalPos != null) {
+      final hx = hoverLocalPos!.dx;
+      final hy = hoverLocalPos!.dy;
+      if (hx >= padLeft &&
+          hx <= padLeft + plotW &&
+          hy >= padTop &&
+          hy <= padTop + plotH) {
+        final col = (hx - padLeft).floor().clamp(0, cols.length - 1);
+        hoverCol = col;
+        hoverTsUs = win.startUs +
+            (((col + 0.5) / plotW) * (win.endUs - win.startUs)).round();
+        final cursorPaint = Paint()
+          ..color = cursorColor
+          ..strokeWidth = 1;
+        canvas.drawLine(
+          Offset(xForCol(col), padTop),
+          Offset(xForCol(col), padTop + plotH),
+          cursorPaint,
+        );
+        if (cols[col].hasData) {
+          hoverY = (cols[col].min + cols[col].max) / 2;
+          final yPx = yForVal(hoverY);
+          canvas.drawLine(
+            Offset(padLeft, yPx),
+            Offset(padLeft + plotW, yPx),
+            cursorPaint,
+          );
+          canvas.drawCircle(
+            Offset(xForCol(col), yPx),
+            3,
+            Paint()..color = lineColor,
+          );
+        }
+      }
+    }
+
     canvas.restore();
 
+    // Cursor readout box (outside the clip so it can overlay labels).
+    if (hoverCol != null) {
+      final tStr = hoverTsUs != null ? _fmtTime(hoverTsUs) : '—';
+      final yStr = hoverY != null ? hoverY.toStringAsFixed(3) : '—';
+      _drawReadout(canvas, 'x=$tStr  y=$yStr',
+          Offset(padLeft + 4, padTop + 2));
+    }
+
     // Axes labels.
     _drawText(canvas, '${yMax.toStringAsFixed(2)}',
         Offset(padLeft - 4, padTop), align: TextAlign.right);
@@ -157,6 +220,44 @@ class ChartPainter extends CustomPainter {
         align: TextAlign.right);
   }
 
+  void _drawReadout(Canvas c, String s, Offset where) {
+    final textColor =
+        isDark ? const Color(0xFFEEEEEE) : const Color(0xFF222222);
+    final bgColor =
+        isDark ? const Color(0xCC2A2B2E) : const Color(0xCCFFFFFF);
+    final borderColor =
+        isDark ? const Color(0x66FFFFFF) : const Color(0x44000000);
+    final tp = TextPainter(
+      text: TextSpan(
+        text: s,
+        style: TextStyle(
+          fontFamily: 'monospace',
+          fontSize: 10,
+          color: textColor,
+        ),
+      ),
+      textDirection: TextDirection.ltr,
+    )..layout();
+    final bgRect = Rect.fromLTWH(
+      where.dx,
+      where.dy,
+      tp.width + 8,
+      tp.height + 4,
+    );
+    c.drawRRect(
+      RRect.fromRectAndRadius(bgRect, const Radius.circular(3)),
+      Paint()..color = bgColor,
+    );
+    c.drawRRect(
+      RRect.fromRectAndRadius(bgRect, const Radius.circular(3)),
+      Paint()
+        ..color = borderColor
+        ..style = PaintingStyle.stroke
+        ..strokeWidth = 0.5,
+    );
+    tp.paint(c, Offset(where.dx + 4, where.dy + 2));
+  }
+
   void _drawText(Canvas c, String s, Offset where,
       {TextAlign align = TextAlign.left}) {
     final tp = TextPainter(