Improve performance by reducing repaints

Author: h65wang

lib/chart_painter.dart

@@ -273,7 +273,8 @@ class ChartPainter extends CustomPainter {
   }
 
   @override
-  bool shouldRepaint(ChartPainter oldDelegate) => true;
+  bool shouldRepaint(ChartPainter oldDelegate) =>
+      params.shouldRepaint(oldDelegate.params);
 }
 
 extension ElementAtOrNull<E> on List<E> {

lib/interactive_chart.dart

@@ -141,13 +141,15 @@ class _InteractiveChartState extends State<InteractiveChart> {
             duration: Duration(milliseconds: 300),
             curve: Curves.easeOut,
             builder: (_, PainterParams params, __) {
-              return CustomPaint(
-                size: size,
-                painter: ChartPainter(
-                  params: params,
-                  getTimeLabel: widget.timeLabel ?? defaultTimeLabel,
-                  getPriceLabel: widget.priceLabel ?? defaultPriceLabel,
-                  getOverlayInfo: widget.overlayInfo ?? defaultOverlayInfo,
+              return RepaintBoundary(
+                child: CustomPaint(
+                  size: size,
+                  painter: ChartPainter(
+                    params: params,
+                    getTimeLabel: widget.timeLabel ?? defaultTimeLabel,
+                    getPriceLabel: widget.priceLabel ?? defaultPriceLabel,
+                    getOverlayInfo: widget.overlayInfo ?? defaultOverlayInfo,
+                  ),
                 ),
               );
             },

lib/painter_params.dart

@@ -83,6 +83,29 @@ class PainterParams {
       trailingTrend: b.trailingTrend,
     );
   }
+
+  bool shouldRepaint(PainterParams other) {
+    if (candles.length != other.candles.length) return true;
+
+    if (size != other.size ||
+        candleWidth != other.candleWidth ||
+        startOffset != other.startOffset ||
+        xShift != other.xShift) return true;
+
+    if (maxPrice != other.maxPrice ||
+        minPrice != other.minPrice ||
+        maxVol != other.maxVol ||
+        minVol != other.minVol) return true;
+
+    if (tapPosition != other.tapPosition) return true;
+
+    if (leadingTrend != other.leadingTrend ||
+        trailingTrend != other.trailingTrend) return true;
+
+    if (style != other.style) return true;
+
+    return false;
+  }
 }
 
 class PainterParamsTween extends Tween<PainterParams> {