feat: 파이 차트 생성하는 CustomPainter 구현 (#21)

* feat: 파이 차트 생성하는 CustomPainter 구현

* fix: 리스트 비교 오류 수정

Author: Neibce

frontend/ongi/lib/widgets/custom_chart_painter.dart

@@ -0,0 +1,261 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/foundation.dart';
+import 'dart:math';
+
+class CustomChartPainter extends CustomPainter {
+  final List<double> percentages;
+
+  CustomChartPainter({required this.percentages});
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    final Offset center = Offset(size.width / 2, size.height / 2);
+    final double outerRadius = size.width / 2;
+    final double innerRadius = outerRadius * 0.65;
+
+    final int segmentCount = percentages.length;
+    final double totalAngle = 2 * pi;
+    final double gapAngle = 0.185;
+    final double totalGaps = gapAngle * segmentCount;
+
+    final double totalPercentage = percentages.reduce((a, b) => a + b);
+    final List<double> normalizedPercentages = percentages
+        .map((p) => p / totalPercentage)
+        .toList();
+
+    final List<double> segmentAngles = normalizedPercentages
+        .map((p) => p * (totalAngle - totalGaps))
+        .toList();
+
+    final LinearGradient gradient = LinearGradient(
+      begin: Alignment.topRight,
+      end: Alignment.bottomLeft,
+      colors: [Color(0xFFFD6C01), Color(0xFFBFECFF)],
+      stops: [0.1, 0.9],
+    );
+
+    final shader = gradient.createShader(
+      Rect.fromCircle(center: center, radius: outerRadius),
+    );
+    final double outerCornerRadius = 10.0;
+    final double innerCornerRadius = outerCornerRadius * 0.65;
+
+    Paint shadowPaint = Paint()
+      ..color = Colors.black26
+      ..strokeWidth = outerRadius - innerRadius + 35
+      ..style = PaintingStyle.stroke
+      ..maskFilter = MaskFilter.blur(BlurStyle.normal, 4.0);
+
+    Paint whitePaint = Paint()
+      ..color = Colors.white
+      ..strokeWidth = outerRadius - innerRadius + 35
+      ..style = PaintingStyle.stroke;
+
+    Offset shadowOffset = Offset(center.dx, center.dy + 2);
+    canvas.drawArc(
+      Rect.fromCircle(
+        center: shadowOffset,
+        radius: (outerRadius + innerRadius) / 2,
+      ),
+      0,
+      2 * pi,
+      false,
+      shadowPaint,
+    );
+
+    canvas.drawArc(
+      Rect.fromCircle(center: center, radius: (outerRadius + innerRadius) / 2),
+      0,
+      2 * pi,
+      false,
+      whitePaint,
+    );
+
+    double currentAngle = -pi / 2 + gapAngle / 2;
+
+    for (int i = 0; i < segmentCount; i++) {
+      final double startAngle = currentAngle;
+      final double endAngle = startAngle + segmentAngles[i];
+      currentAngle = endAngle + gapAngle;
+
+      Path path = Path();
+
+      path.arcTo(
+        Rect.fromCircle(center: center, radius: outerRadius),
+        startAngle,
+        segmentAngles[i],
+        false,
+      );
+
+      path.arcTo(
+        Rect.fromCircle(center: center, radius: innerRadius),
+        endAngle,
+        -segmentAngles[i],
+        false,
+      );
+
+      final Offset startInner = Offset(
+        center.dx + innerRadius * cos(startAngle),
+        center.dy + innerRadius * sin(startAngle),
+      );
+      final Offset startOuter = Offset(
+        center.dx + outerRadius * cos(startAngle),
+        center.dy + outerRadius * sin(startAngle),
+      );
+
+      final Offset endInner = Offset(
+        center.dx + innerRadius * cos(endAngle),
+        center.dy + innerRadius * sin(endAngle),
+      );
+      final Offset endOuter = Offset(
+        center.dx + outerRadius * cos(endAngle),
+        center.dy + outerRadius * sin(endAngle),
+      );
+
+      path.moveTo(endOuter.dx, endOuter.dy);
+      path.addOval(
+        Rect.fromCircle(
+          center: getPointAtDistance(endOuter, endInner, outerCornerRadius),
+          radius: outerCornerRadius,
+        ),
+      );
+      path.addOval(
+        Rect.fromCircle(
+          center: getPointAtDistance(endInner, endOuter, innerCornerRadius),
+          radius: innerCornerRadius,
+        ),
+      );
+
+      path.addOval(
+        Rect.fromCircle(
+          center: getPointAtDistance(startOuter, startInner, outerCornerRadius),
+          radius: outerCornerRadius,
+        ),
+      );
+      path.addOval(
+        Rect.fromCircle(
+          center: getPointAtDistance(startInner, startOuter, innerCornerRadius),
+          radius: innerCornerRadius,
+        ),
+      );
+
+      Offset ovalEndOuter = moveAlongCircle(
+        center: center,
+        radius: outerRadius - outerCornerRadius,
+        startAngle: endAngle,
+        distance: outerCornerRadius,
+      );
+      Offset ovalEndInner = moveAlongCircle(
+        center: center,
+        radius: innerRadius + innerCornerRadius,
+        startAngle: endAngle,
+        distance: innerCornerRadius,
+      );
+
+      Offset ovalStartOuter = moveAlongCircle(
+        center: center,
+        radius: outerRadius - outerCornerRadius,
+        startAngle: startAngle,
+        distance: 0,
+      );
+      Offset ovalStartInner = moveAlongCircle(
+        center: center,
+        radius: innerRadius + innerCornerRadius,
+        startAngle: startAngle,
+        distance: 0,
+      );
+
+      path.addPath(
+        buildSkewedRect(
+          ovalEndOuter,
+          ovalEndInner,
+          outerCornerRadius,
+          innerCornerRadius,
+        ),
+        Offset.zero,
+      );
+
+      path.addPath(
+        buildSkewedRect(
+          ovalStartOuter,
+          ovalStartInner,
+          outerCornerRadius,
+          innerCornerRadius,
+        ),
+        Offset.zero,
+      );
+      path.close();
+
+      final Paint segmentPaint = Paint()
+        ..shader = shader
+        ..style = PaintingStyle.fill;
+
+      canvas.drawPath(path, segmentPaint);
+    }
+  }
+
+  Offset getPointAtDistance(Offset p1, Offset p2, double distance) {
+    final dx = p2.dx - p1.dx;
+    final dy = p2.dy - p1.dy;
+    final len = sqrt(dx * dx + dy * dy);
+
+    if (len == 0) return p1; // 두 점이 같을 경우
+
+    final ratio = distance / len;
+    return Offset(p1.dx + dx * ratio, p1.dy + dy * ratio);
+  }
+
+  Path buildSkewedRect(
+    Offset topLeft,
+    Offset bottomLeft,
+    double outerWidth,
+    double innerWidth,
+  ) {
+    final dx = bottomLeft.dx - topLeft.dx;
+    final dy = bottomLeft.dy - topLeft.dy;
+    final length = sqrt(dx * dx + dy * dy);
+
+    final nx = -dy / length;
+    final ny = dx / length;
+
+    final topRight = Offset(
+      topLeft.dx + nx * outerWidth,
+      topLeft.dy + ny * outerWidth,
+    );
+    final bottomRight = Offset(
+      bottomLeft.dx + nx * innerWidth,
+      bottomLeft.dy + ny * innerWidth,
+    );
+
+    final path = Path()
+      ..moveTo(topLeft.dx, topLeft.dy)
+      ..lineTo(bottomLeft.dx, bottomLeft.dy)
+      ..lineTo(bottomRight.dx, bottomRight.dy)
+      ..lineTo(topRight.dx, topRight.dy)
+      ..close();
+
+    return path;
+  }
+
+  Offset moveAlongCircle({
+    required Offset center,
+    required double radius,
+    required double startAngle,
+    required double distance,
+  }) {
+    if (radius == 0) return center;
+
+    final double deltaAngle = distance / radius;
+    final double newAngle = startAngle + deltaAngle;
+
+    return Offset(
+      center.dx + radius * cos(newAngle),
+      center.dy + radius * sin(newAngle),
+    );
+  }
+
+  @override
+  bool shouldRepaint(covariant CustomChartPainter oldDelegate) {
+    return !listEquals(percentages, oldDelegate.percentages);
+  }
+}