CircleGeometry constructor

CircleGeometry({ double radius = 1, int segments = 8, double thetaStart = 0, double thetaLength = pi * 2, })

radius — Radius of the circle, default = 1.

segments — Number of segments (triangles), minimum = 3, default = 32.

thetaStart — Start angle for first segment, default = 0 (three o'clock position).

thetaLength — The central angle, often called theta, of the circular sector. The default is 2*pi, which makes for a complete circle.

Implementation

CircleGeometry({
  double radius = 1,
  int segments = 8,
  double thetaStart = 0,
  double thetaLength = pi * 2
}):super() {
  parameters = {
    "radius": radius,
    "segments": segments,
    "thetaStart": thetaStart,
    "thetaLength": thetaLength
  };

  segments = max(3, segments);

  // buffers

  List<int> indices = [];
  List<double> vertices = [];
  List<double> normals = [];
  List<double> uvs = [];

  // helper variables

  final vertex = Vector3.zero();
  final uv = Vector2.zero();

  // center point

  vertices.addAll([0, 0, 0]);
  normals.addAll([0, 0, 1]);
  uvs.addAll([0.5, 0.5]);

  for (int s = 0, i = 3; s <= segments; s++, i += 3) {
    final segment = thetaStart + s / segments * thetaLength;

    // vertex

    vertex.x = radius * cos(segment);
    vertex.y = radius * sin(segment);

    vertices.addAll([vertex.x.toDouble(), vertex.y.toDouble(), vertex.z.toDouble()]);

    // normal

    normals.addAll([0.0, 0.0, 1.0]);

    // uvs

    uv.x = (vertices[i] / radius + 1) / 2;
    uv.y = (vertices[i + 1] / radius + 1) / 2;

    uvs.addAll([uv.x.toDouble(), uv.y.toDouble()]);
  }

  // indices

  for (int i = 1; i <= segments; i++) {
    indices.addAll([i, i + 1, 0]);
  }

  // build geometry

  setIndex(indices);
  setAttribute(Attribute.position,Float32BufferAttribute.fromList(vertices, 3, false));
  setAttribute(Attribute.normal,Float32BufferAttribute.fromList(normals, 3, false));
  setAttribute(Attribute.uv, Float32BufferAttribute.fromList(uvs, 2, false));
}