SlimDx绘制点图元的问题

问题：点图元在自己创建的三维环境里渲染不出来，代码如下：

GMCustomVertex.PositionNormalColored wellPart = new GMCustomVertex.PositionNormalColored[wellsCount];
wellPart[i].X = (wells[i].X - point.X) * 10;
wellPart[i].Y = (wells[i].Y - point.Y) * 10;
wellPart[i].Z = 600f * 5;
wellPart[i].Color = Color.White.ToArgb();
drawArgs.device.SetTransform(TransformState.Projection, drawArgs.WorldCamera.projectionMatrix);
drawArgs.device.SetTransform(TransformState.View, drawArgs.WorldCamera.viewMatrix);
drawArgs.device.SetTransform(TransformState.World, drawArgs.WorldCamera.worldMatrix);
drawArgs.device.VertexFormat = GMCustomVertex.PositionNormalColored.Format;
drawArgs.device.DrawUserPrimitives(PrimitiveType.PointList, wellsCount, wellPart);

解决办法：缺少顶点法线。

wellPart[i].Normal = new Vector3(0, 0, 1);