feat: Add Line3D mesh component [flame_3d]

packages/flame_3d/lib/src/components/line_3d.dart

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+import 'dart:math' as math;
+import 'dart:ui';
+
+import 'package:flame_3d/components.dart';
+import 'package:flame_3d/game.dart';
+import 'package:flame_3d/resources.dart';
+
+class Line3D extends MeshComponent {
+  Line3D._({
+    required double radius,
+    required double height,
+    required Color color,
+  }) : super(
+          mesh: CylinderMesh(
+            radius: radius,
+            height: height,
+            material: SpatialMaterial()..albedoColor = color,
+          ),
+        );
+
+  factory Line3D.generate({
+    required Vector3 start,
+    required Vector3 end,
+    required Color color,
+    double radius = 0.01,
+  }) {
+    final line = Line3D._(
+      radius: radius,
+      height: start.distanceTo(end),
+      color: color,
+    );
+    line.transform.setFrom(_calculateTransform(start, end));
+    return line;
+  }
+
+  static Transform3D _calculateTransform(
+    Vector3 start,
+    Vector3 end,
+  ) {
+    final direction = end - start;
+    final length = direction.length;
+
+    final bottomCenter = Vector3(0, -length / 2, 0);
+    final topCenter = Vector3(0, length / 2, 0);
+
+    final translation = start - bottomCenter;
+
+    final rotation = _calculateRotationMatrix(
+      bottomCenter: translation + bottomCenter,
+      topCenter: translation + topCenter,
+      target: end,
+    );
+
+    final translationMatrix = Matrix4.translation(translation);
+    final rotationMatrix = _rotateAroundPoint(rotation, start);
+    final transform = rotationMatrix.multiplied(translationMatrix);
+
+    return Transform3D.fromMatrix4(transform);
+  }
+
+  static Matrix4 _calculateRotationMatrix({
+    required Vector3 bottomCenter,
+    required Vector3 topCenter,
+    required Vector3 target,
+  }) {
+    final origin = (topCenter - bottomCenter).normalized();
+    final dest = (target - bottomCenter).normalized();
+
+    final normal = origin.cross(dest);
+    if (normal.length == 0) {
+      return Matrix4.identity();
+    }
+
+    final dotProduct = origin.dot(dest);
+    final angle = math.acos(dotProduct);
+
+    return Matrix4.identity()..rotate(normal, angle);
+  }
+
+  static Matrix4 _rotateAroundPoint(Matrix4 rotation, Vector3 point) {
+    return Matrix4.translation(point)
+        .multiplied(rotation)
+        .multiplied(Matrix4.translation(-point));
+  }
+}

packages/flame_3d/test/components/line_3d_test.dart

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+import 'dart:ui';
+
+import 'package:flame_3d/core.dart';
+import 'package:flame_3d/src/components/line_3d.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('Line 3D Mesh Component', () {
+    test('can create line', () {
+      final line = Line3D.generate(
+        start: Vector3(0, -1, 0),
+        end: Vector3(0, 1, 0),
+        color: const Color(0xFFFFFFFF),
+      );
+
+      expect(
+        line.transform.transformMatrix,
+        equals(Matrix4.identity()),
+      );
+    });
+  });
+}