This is a personal project for ice halo simulation. It is inspired by HaloPoint 2.0 and HaloSim 3.0. Unfortunately the author of HaloPoint seems have stopped developing.

For a start this program is written in matlab though matlab is often poured scorn on for its slow performance. It is a prototype, on which I test my algorithms. Later developing and latest updates will be on C++ codes. Also, matlab codes contain some small tools for visualization.

Details including how to build and run can be found on following pages. NOTE: I've stopped developing on matlab codes. These are just legacy codes remained here for reference.

• C++ codes
• Matlab codes

• High speed.
  The simulation program is 50~100 times faster than HaloPoint. On general cases this program runs at a speed of 140k~200k rays per second. On multi-scattering cases it runs as faster as 50k~80k rays per second. On the contrary, HaloPoint may cost minutes to render 100k rays, and even hours on multi-scattering cases.

• Natural and vivid color.
  Based on my another project Spectrum Renderer, a matlab tool to render colors with given spectrum, this simulation program can render very natural and vivid color.
  

• Full multi-scattering support.
  This program is designed to handle multi-scattering cases. As a reference, HaloPoint handles multi-scattering via a very tricky workaround, thus it is hard to simulate 44-degree parhelia. And my program allows you to simulate any multi-scattering scenario freely. Following multi-scattering display is generated in 14 minutes on my Macbook pro, with totally 72 million starting rays traced.
  

• Customized crystal model. This program has a simple built-in parser for .obj file and users can thus simulate with any complex crystal models, e.g. hollow hex-cylinder, created via 3D modeling software.

1. HaloPoint 2.0 & HaloSim 3.0
2. Rapidjson

本项目是一个个人项目, 受到 HaloPoint 2.0 和 HaloSim 3.0 的启发. 但不幸的是 HaloPoint 原作者似乎停止更新了.

最开始我是从 matlab 代码开始的, 虽然 matlab 经常被人吐槽很慢, 但其实用于开发原型和验证算法来说足够了. 这个项目涉及大量的矩阵和向量计算, 恰恰是 matlab 擅长的.

在 matlab 代码上验证了算法后, 后续开发都将在 C++ 代码上进行. 此外 matlab 代码还包括了几个小工具, 用于一些可视化的任务.

关于构建和运行的细节, 请参见下面的页面. 注意: matlab 代码我已不再开发, 这里保留仅作为参考.

• C++ 代码
• Matlab 代码

• 速度快
  本模拟程序追踪光线效率非常优秀, 比 HaloPoint 快 50~100 倍. 在多晶模拟的情况下, 比 HaloPoint 优势更大. 对于一般情况, 本模拟程序模拟的速度约为每秒 14~20 万光线, 在多晶的情况下约为 5~8 万每秒. 相对的, HaloPoint 模拟 10 万光线常常需要分钟级别的时间, 而多晶情况下更是需要好几个小时.

• 自然而鲜艳的色彩表现
  本模拟程序的色彩模拟是基于我的另一个个人项目 Spectrum Renderer, 那是一个 matlab 小工具, 可以对任意光谱所表现出来的颜色进行模拟.
  

• 对多晶模拟的完整支持
  本模拟程序可以完整地模拟多晶场景, 与普通单晶场景的操作没有区别, 不需特殊对待. 作为对比, HaloPoint 采用了一种非常绕的方式来勉强模拟多晶场景, 并且难以模拟 44 度幻日. 而本模拟程序可以让用户自由模拟任意的多晶场景. 下图所示场景只需要不到 14 分钟即可模拟渲染完. 总计追踪约 7200 万条初始光线.
  

• 用户自定义的冰晶形状
  本模拟程序实现了一个简单的 .obj 文件 解析器, 因此支持用户通过 3D 建模软件自定义复杂形状的冰晶, 比如镂空的柱晶.

1. HaloPoint 2.0 & HaloSim 3.0
2. Rapidjson