MeshGeometry.combine constructor Null safety

Implementation

factory MeshGeometry.combine(List<MeshGeometry> meshes) {
  if (meshes.length < 2) {
    throw Exception(
        'Must provide at least two MeshGeometry instances to combine.');
  }

  // When combining meshes they must all have a matching set of VertexAttribs
  final firstMesh = meshes[0];
  var totalVerts = firstMesh.length;
  var totalIndices =
      firstMesh.indices != null ? firstMesh.indices!.length : 0;
  for (var i = 1; i < meshes.length; ++i) {
    final srcMesh = meshes[i];
    if (!firstMesh.attribsAreCompatible(srcMesh)) {
      throw Exception(
          'All meshes must have identical attributes to combine.');
    }
    totalVerts += srcMesh.length;
    totalIndices += srcMesh.indices != null ? srcMesh.indices!.length : 0;
  }

  final mesh =
      MeshGeometry._internal(totalVerts, firstMesh.stride, firstMesh.attribs);

  if (totalIndices > 0) {
    mesh.indices = Uint16List(totalIndices);
  }

  // Copy over the buffer data:
  var bufferOffset = 0;
  var indexOffset = 0;
  var vertexOffset = 0;
  for (var i = 0; i < meshes.length; ++i) {
    final srcMesh = meshes[i];
    mesh.buffer.setAll(bufferOffset, srcMesh.buffer);

    if (totalIndices > 0) {
      for (var j = 0; j < srcMesh.indices!.length; ++j) {
        mesh.indices![j + indexOffset] = srcMesh.indices![j] + vertexOffset;
      }
      vertexOffset += srcMesh.length;
      indexOffset += srcMesh.indices!.length;
    }

    bufferOffset += srcMesh.buffer.length;
  }

  return mesh;
}