『部分工程文件点我下载』
『知乎转载链接』
『有点相关的Unreal Circle演讲』
Summary
因为本文涉及到的内容比较广，关于Niagara最基础的一些部分比如怎么新建、怎样添加使用模块就不详细说明了，没用过的同学可以先看一下Epic官方文档的介绍：
Niagara核心概念
和贾越同学的系列教学直播：
https://www.bilibili.com/video/av73602807
本次工程效果：
为了实现海浪拍到岩石上激起千层浪的感觉，我们可以看到有几个表现上的关键点
- 在岩石附近生成水花
- 水花激起的时机和位置与海水的流动匹配
- 出射速度受到海水运动和石头表面的撞击情况影响
- 激起后水花的体积感
海面的模拟 – Gerstner Waves
游戏里模拟海水的途径是一门艰深的课题，本文就不多涉及了。这里为了制作需要，介绍一下相对直观实用的Gerstner Waves。
在流体动力学中，Gerstner Waves是周期表面重力波的欧拉方程方程的精确解。它计算机图形技术之前很久就出现了，用来描述不可压缩流体的表面波动。
单一Gerstner Wave材质应用在一个平面上的效果如图：
数学时间
我们可以看到每一个点不止有Z轴方向的运动，也有XY轴的运动。并且这不是一个简单的sin波而是带有‘浪尖’的波形，这些都是Gerstner Wave的重要特征。
因为篇幅原因这里就不具体说公式了，本节末尾提供了我做好的材质节点可以直接下载取用。详细算法可以参考：
Chapter 1. Effective Water Simulation from Physical Models
https://developer.download.nvidia.com/books/HTML/gpugems/gpugems_ch01.html
简单说来，定义一个波形的属性有：
[高度, 前进方向, 波长, 陡峭度]
我们定义相位φ
φ = 方向 ⋅ 位置 / 波长 + 频率 * 时间
其中
频率 = sqrt(重力 * 2π / 波长)
那么以
z轴偏移 = 高度 * sin(φ)
xy轴偏移 = 陡峭度 * 高度 * 方向 * cos(φ)
的形式去移动海面的顶点，顶点会沿着椭圆绕圈（左图），一系列的顶点组合在一起就会形成具有浪尖的波形。
引擎内实现
在引擎里的实现可以用HLSL写在Custom节点里，你也可以选择用节点连。执行效率上，节点连出来的公式和HLSL代码没有区别。
材质函数 MF_GerstnerWave
核心部分：
float3 d = float3(sin(DirectionInDegrees * 0.0174533), cos(DirectionInDegrees * 0.0174533), 0); // 为了控制方便，输入并不是一个向量而是角度，这里转换一下
float w = 6.2831854 / L;
float theta = sqrt(6.2831854 * Gravity / L); // 由波长算出频率
float q = Stiffness / (Amplitude * w); // q是控制浪尖陡峭度的系数
float phase = dot((w * d).xy, WorldPosition.xy) – theta * Time; // 喂给cos和sin的相位
float3 offset = float3(q * Amplitude * d.xy * cos(phase), Amplitude * sin(phase)); // 照抄上面公式
这部分我放在了BlueprintUE.com里，点下面链接直接把节点复制粘贴到UE材质编辑器里就可以得到图上的节点：
https://blueprintue.com/blueprint/tt5p124n/
波形叠加
显然，一条波并不能说非常炫酷，Gerstner Wave的典型做法是把多条波叠加在一起。上面提到每条波可以控制的变量有：[高度, 前进方向, 波长, 陡峭度]
要合并多个波形，首先考虑的是波长，因为能组合的波长数量有限（8个已经很多了），我们无法完全参照真实世界的海洋数据，只能尽可能利用能付出的资源。由于波长相似的wave在叠加时看起来更有错综复杂的动态表现，我们可以在输入参数里首先给一个波长的中值LengthMedian，然后让不同wave的波长围绕这个中值变化。这样只要保留所有wave的波长与LenghMedian的比例，就可以通过改变LengthMedian来调整整个海洋的波浪大小：
在定义一组waves的结构FGerstnerWavesParameters中，美术可以在海洋的蓝图Actor上直接填写LengthMedian。
接下来，美术可以手动填写各个wave和LengthMedian的比例，也可以像我一样偷懒，填一个LengthMultiplierRange然后随机选取范围内的比例，在场景里拖动Seed直到随出一个好看的组合。
类似的方法同样适用于高度, 前进方向, 陡峭度。要注意的是，wave的高度和波长存在正相关关系，简单的做法是定义一个常数比例，让每个wave高度和和波长的比例保持一致。而在定义前进方向时会类似的给出一个DirectionRange定义前进方向的范围。
Niagara GPU粒子的生成
匹配水面位移
上面说了这么多，海面Shader内的位移数据其实并不能被外界直接读取，为了让Niagara能获取到海面的位移数据从而实现位置的同步，我们需要额外做一些工作：
方块：Niagara GPU particles
因为Gerstner Wave算法是确定性的，即给定同样的 [ 高度 | 前进方向 | 波长 | 陡峭度 ] 这样一组参数，不管在哪算出来的波形都是一样一样的。所以我们只要把与海面同样的参数传入Niagara System，就可以让Niagara粒子去‘追踪‘海面的粒子。（如上图）
传参
Normal难度：
上面说到，海面的波形是由好几个不同的Gerstner Wave组成，这里我用了8个，那么需要匹配海面的形状，其实在生成浪花时我们不用考虑所有8个waves，只考虑最大的一或两级wave，视觉上就很难看出不完全吻合的细节差别了。
Hard难度:
这一块可选阅读，可以跳过，对下面内容的理解没有影响。
可是如果我觉得这样做身体不适，非想传所有数据达到完美同步呢？ 也不是没有办法。4个参数 x 8组 = 一共32个float变量，手动命名并且在蓝图里拉面条，再在Niagara模块上一个一个拖上去也不是不行.. 如果你想做得灵巧些，我发掘了一个输入数组的hack：
因为Niagara还在beta阶段，一些功能还在持续改进中，这个hack可能以后也不需要。我介绍一下的另一个原因是觉得对增加对Niagara的理解有所帮助。
开始我想把数据通过DrawToRenderTarget写到一张贴图上，让Niagara读，但因为操作太不友好并且不支持CPU粒子放弃了。后来发现Niagara里的Curve型变量是同时支持CPU和GPU的，读取也很方便。我在蓝图里把需要的变量写入到一个Curve asset里，Niagara内reimport更新就可以，很方便。
不过Curve key的格式是有讲究的，Niagara CPU sim在读curve时，直接就读对应位置的key value。但GPU sim上会首先把curve编码成一个1×128像素的Lookup table，然后再读对应位置的数据，这就导致如果key的time位置不是100%对到LUT的像素位置上，encode后会出现偏差，这个偏差在我们现在的应用中是无法容许的。
好在encode的逻辑非常直接，只是取第一个key和最后一个key的time看范围，normalize到[0.0, 1.0]之间：
所以要达到key和LUT的像素对齐，最简单的方式是让time = [0, 1, 2… 127]，这样不需要额外操作，在GPU sim上读取即可。
最后一个key的time是127.0
这样我们就实现了可以在一个curve里记录128个float值。剩下要做的就是再BP里根据一定规则把8个wave的一系列参数编码，再从Niagara模块里通过相同规则解码。这里4个参数*8个wave，规则就是很简单的按照一定间隔记录了32个值。
按照一定间隔，在整数Time上记录了每一组parameters
在Niagara module中通过类似方式解压
定义GPU粒子的碰撞行为
Distance Field Collision
系统提供的collision模块非常健全，包括CPU trace碰撞，GPU depth / distance field碰撞等分支可以在下拉菜单中选择使用。我们这里使用GPU distance field碰撞，depth碰撞比较适合比较粗犷的效果，比如下雨下雪，稍微有点问题也看不出来，但如果水浪使用depth碰撞，岩石背面屏幕看不到的地方就会出错。
我们想有一些比较细腻的控制逻辑，比如这里水花撞到石头上，如果用默认的collision碰撞，反弹是朝着下图绿色的反射向量方向飞出去的，而流体撞到刚体的行为并不是这样完美的反弹，我们更想让它偏向下图紫色的角度。
下面三个gif分别展示不同反射角度的视觉：
定义这样的碰撞行为需要自己写模块，幸运的是这种逻辑都可以用Niagara的节点实现。引擎提供的Collision模块本身是一个宝藏，里面有各种碰撞的实现方式和模块编辑的best practice。在Collision – CollisionQueryAndResponse模块中我们探索一下可以发现：
点进去最底层的模块是：
即给出world position获得global distance field的数值和gradient，和材质里的DistanceToNearestSurface / DistanceFieldGradient结果是一样的，都是GPU内的query。
知道了这些，我们就可以很方便的自己写一个简单的collision判断：
并且在后面接上上面说到的反射角和切线角的逻辑–如果发现水浪粒子进行了第一次和岩石碰撞，那么就沿着我们想要的角度给一个初速度：
距离优化
同时因为有了distance field信息，可以在particle spawn时判断水浪粒子是否在岩石附近，如果不在就直接删除。
Smear
水花的材质想做好也是一项涉及很广的任务，我这里就是用了一个比较简单的云的贴图，稍微加工了下。值得一提的是通过particle的速度可以在材质里实现速度拉伸效果，对表达浪花飞溅的夸张形态非常有帮助：
实现方式也很简单，因为粒子sprite是朝向camera的，我们只要以local position和移动速度的点积缩放sprite即可：
Easy to recommend, the content speaks for itself without needing additional praise from me, and a stop at timbertrailmerchantgallery only adds more reasons to send people this way, the kind of generous resource that benefits its readers without demanding anything in return is increasingly rare and worth recognising clearly today across the broader open internet.
Took longer than expected to finish because I kept stopping to think, and a stop at shorevolume did the same to me, content that provokes thought rather than just delivering information is in a different category and the team here is clearly working at that higher level rather than just cranking out posts.
A piece that exhibited the kind of patience that good writing requires, and a look at skiffvantage continued that patient quality, hurried writing is easy to spot and this site reads as having been written without time pressure which produces a different feel than the rushed content that dominates much of the modern blog space.
Solid little post, the kind that does not need to be flashy because the substance is doing the work, and a look at waveharbormerchantgallery kept that quiet confidence going across the site, this is what writing looks like when the writer trusts the content to land on its own without theatrics or unnecessary attention seeking behaviour.
A piece that suggested careful editing without showing the marks of the editing, and a look at daisyharborcommercegallery continued that invisible polish, the best editing disappears into the prose and this site reads as having been edited with skill that does not announce itself which is the highest compliment I can offer any blog content.
However many similar pages I have read this one taught me something new, and a stop at glyjay added more new material, content that contributes genuinely fresh information rather than recycling what is already widely available is content with real informational value and this site is providing that informational freshness at a notable rate.
Even across multiple posts the writers voice has remained consistent in a way I appreciate, and a stop at sloganturban continued that voice, sites that maintain editorial consistency across many pieces have something most sites lack and this one has clearly worked out how to keep its voice steady across what reads as a growing archive.
Worth recognising the absence of the usual blog tropes here, and a look at embermeadowmerchantgallery continued that fresh quality, sites that avoid the standard moves of the medium read as more original even when the content is on familiar topics and this one has clearly chosen its own path through the conventional terrain skilfully.
aviator игра мостбет https://mostbet91325.help/
During a reading session that included several other sources this one stood out, and a look at trumpetsixth continued the standout quality, the side by side comparison of sources during research is a useful exercise and this site has been winning those comparisons for me consistently across multiple research sessions during the last week.
Most of the time I bounce off similar pages within seconds, and a stop at vinylvessel held me longer than I would have predicted, the ability to convert a likely bouncing visitor into an engaged reader is a quality signal and this site has demonstrated that conversion ability across multiple visits where I expected to bounce.
Now noticing that the post did not mention the writer at all, focus stayed on the topic, and a look at fiabush continued that author absent quality, content that disappears the writer to focus on the substance is a particular kind of generosity and this site has clearly chosen the substance over the personality consistently.
кредит под залог недвижимости рефинансирование ипотеки
Honestly the simplicity of the explanation made the topic click for me in a way other writeups had not, and a look at mossharborcommercegallery continued that clarity into related areas, when a writer gets the level of explanation right the reader does the heavy lifting themselves and the post just enables it.
Народ всем привет Нужно сдвинуть санузел Мосжилинспекция завернёт любые работы Потратил кучу времени Короче, единственное что реально работает — перепланировка квартир с полным сопровождением И в инспекцию подадут В общем, сохраняйте себе — согласование переоборудования квартиры https://pereplanirovka-kvartir-ksd.ru Потом штраф и суды Перешлите тому кто затеял ремонт
Слушайте кто с ремонтом Нужно сдвинуть санузел Мосжилинспекция завернёт любые работы Нервов потратил — пипец Короче, единственное что реально работает — перепланировка квартиры в Москве с гарантией И в инспекцию подадут В общем, там и примеры и цены — перепланировка помещения https://pereplanirovka-kvartir-ksd.ru Потом штраф и суды Перешлите тому кто затеял ремонт
Слушайте кто с ремонтом Затеял ремонт в хрущёвке Мосжилинспекция завернёт любые работы Я уже намучился Короче, нормальные ребята которые делают всё под ключ — перепланировка квартир с полным сопровождением И чертежи сделают В общем, смотрите сами по ссылке — перепланировка москва https://pereplanirovka-kvartir-ksd.ru Без проекта даже не начинайте Перешлите тому кто затеял ремонт
Recommended without hesitation if you care about careful coverage of this topic, and a stop at saddleswamp reinforced the recommendation, the bar I set for unhesitating recommendations is fairly high and this site has cleared it through the cumulative weight of multiple consistently good pieces rather than through any single standout post which is meaningful.
Народ у кого дети А домашние задания — это вообще ад А знаний реальных ноль Короче, нашли отличный выход — школы дистанционного обучения с индивидуальным подходом Аттестат государственный В общем, смотрите сами по ссылке — онлайн школа в москве https://shkola-onlajn-vem.ru Не мучайте себя и детей Перешлите другим родителям
Good quality through and through, no rough edges and no signs of being rushed, and a quick look at hoxhem kept the same polish going, the kind of site that respects its own brand by maintaining consistency across pages which is something I always appreciate as a reader looking for trustworthy information online today.
Reading this fit naturally into my afternoon walk because I was reading on my phone, and a stop at timbertrailmerchantgallery continued well in that walking format, content that survives mobile reading without becoming awkward is content with format flexibility and this site has clearly thought about how it reads across different devices today.
Слушайте кто ремонт затеял Замучился я с перепланировкой Штрафы огромные если без согласования Я уже голову сломал Короче, единственные кто берётся за всё — перепланировка квартир с полным пакетом документов И техзаключение оформили В общем, смотрите сами по ссылке — перепланировка квартиры согласование https://pereplanirovka-kvartir-owy.ru Потом себе дороже выйдет Перешлите тому кто тоже ремонт затеял
A piece that handled the topic with appropriate weight without becoming portentous, and a look at solacevelour continued that calibrated seriousness, content that takes itself seriously without becoming pompous is something this site has clearly figured out and the balance shows up in every piece I have read across multiple sessions now.
Approaching this site through a casual link click and being surprised by what I found, and a look at tweedvolume extended the surprise, the rare experience of stumbling into excellent independent content rather than predictable mediocrity is one of the actual remaining pleasures of casual web browsing and this site provided it cleanly.
Reading this slowly and letting each paragraph land before moving on, and a stop at shorevolume earned the same patient approach, content that rewards slow reading rather than speed is content with real density and the writers here are clearly producing work that benefits from the careful eye rather than the rushed scan.
A nicely understated post that does not shout for attention, and a look at frostridgemerchantgallery maintained the same quiet quality, understatement is a stylistic choice that distinguishes serious writing from attention seeking writing and this site has clearly committed to the understated approach as a core editorial value rather than just a phase.
Now feeling confident that this site will continue producing work I will want to read, and a look at hiltgem extended that confidence into the future, projecting forward from current quality to expected future quality is something I do for sites I genuinely follow and this one has earned that forward looking trust clearly today.
1win autentificare cu telefon 1win autentificare cu telefon
Glad the writer kept this short rather than padding it out, the points stand on their own without needing extra context, and a look at velvetbrookmerchantgallery kept the same approach going, brevity is a sign of confidence in the substance and the team here clearly trusts their content to land without filler.
Speaking as someone who used to recommend blogs frequently and got out of the habit this site is rekindling that impulse, and a look at arobell extended the rekindling, the recovery of an old habit triggered by encountering work that justifies it is itself a small kind of pleasure and this site is providing that recovery experience.
A particular pleasure to read this with a fresh coffee, and a look at daisyharborcommercegallery extended the pleasure across more pages, content that pairs well with quiet morning rituals is something I have come to value highly and this site has the kind of energy that fits naturally into a calm reading routine.
Useful reading material, the kind I can hand off to someone newer to the topic without worrying about confusing them, and a quick look at kraftgroove confirmed the same beginner friendly tone runs throughout the site which is great for sharing with people just starting their learning journey on this particular topic.
High quality writing, no marketing speak and no buzzwords that mean nothing, and a stop at glyjay kept that going, simple direct content that actually communicates something is harder to find than it should be and this is one of the rare places that gets it right consistently across many different posts.
Found this through a search that was generic enough I did not expect quality results, and a look at waveharbormerchantgallery continued the surprisingly good experience, search engines occasionally still surface excellent independent content if you scroll past the obvious paid and high authority results which is reassuring to remember sometimes.
1win depunere instant https://1win15726.help/
Looking at this objectively the editorial quality is hard to deny even setting aside personal taste, and a stop at nyxsip maintained the same objective quality, the gap between what I personally enjoy and what is objectively well crafted exists and this site clears both bars simultaneously which is rarer than it sounds.
Now thinking I want more sites built on this kind of editorial foundation, and a stop at fribrag extended that wish into a broader hope, sites built on substance and care rather than on metrics and growth are the kind of sites I want to see more of and this one is a small example worth supporting.
Halfway through I knew I would finish the post, and a stop at heathfoam also held me through to the end, content that signals its quality early and then sustains it is content with real internal consistency and this site has clearly figured out how to maintain quality from opening sentence through to closing thought.
Well crafted post, the structure flows naturally from one point to the next without forcing transitions, and a stop at sweatertorso kept the same flow going, you can tell when a writer has thought about how their content reads rather than just what it contains and this is one of those examples.
Appreciated how the writer anticipated the questions a reader might have along the way, and a stop at skifftornado continued that thoughtful approach, you can tell when content has been edited with the reader in mind versus just published as a first draft and this is clearly the former approach across what I read.
Picked up several practical tips that I plan to try out this week, and a look at nightfallcommercegallery added a few more I will be testing alongside, content with practical hooks that connect to my actual life is the kind that earns my repeat attention rather than the merely interesting that I forget within a day.
mostbet ponowne otwarcie konta http://mostbet18361.online/
Народ у кого дети Каждое утро как на войну собираться Ребёнок к вечеру как выжатый лимон Короче, реально крутая система — школа онлайн без стресса и нервов Никаких сборов в 8 утра В общем, смотрите сами по ссылке — онлайн средняя школа https://shkola-onlajn-vem.ru Переходите на нормальное обучение Перешлите другим родителям
Слушайте кто ремонт затеял Хотел стену снести между комнатами Инспекция не пропускает ничего Потратил кучу времени впустую Короче, нашел наконец нормальных специалистов — узаконивание перепланировки без нервотрёпки И чертежи сделали В общем, смотрите сами по ссылке — перепланировка квартир перепланировка квартир Не начинайте без проекта Перешлите тому кто тоже ремонт затеял
Родители всем привет А домашние задания — это вообще ад А знаний реальных ноль Короче, нашли отличный выход — онлайн обучение для школьников в удобном режиме Аттестат государственный В общем, жмите чтобы не потерять — школы дистанционного обучения школы дистанционного обучения Переходите на нормальное обучение Перешлите другим родителям
Народ у кого дети в школе Вечные двойки и тройки в дневнике Никакого интереса к учёбе Короче, реально удобный формат — школа онлайн с лицензией и зачислением Преподаватели профи В общем, сохраняйте себе — московская онлайн школа https://shkola-onlajn-pqs.ru Хватит мучить себя и ребёнка Перешлите другим родителям
Люди помогите советом Хотел стену снести между комнатами А тут оказывается столько бумаг Нервов просто не осталось Короче, единственные кто берётся за всё — перепланировка квартир с полным пакетом документов И чертежи сделали В общем, там и примеры и расценки — перепланировка помещения https://pereplanirovka-kvartir-owy.ru Не начинайте без проекта Перешлите тому кто тоже ремонт затеял
Слушайте кто ремонт затеял Планировал объединить кухню с гостиной Инспекция не пропускает ничего Я уже голову сломал Короче, ребята реально толковые — услуги по перепланировке квартир под ключ И техзаключение оформили В общем, смотрите сами по ссылке — узаконивание перепланировки https://pereplanirovka-kvartir-owy.ru Потом себе дороже выйдет Перешлите тому кто тоже ремонт затеял
Мамы и папы всем привет Домашка на весь вечер Никакого интереса к знаниям Короче, нашли идеальное решение — школа онлайн с индивидуальным расписанием Ребёнок занимается с удовольствием В общем, смотрите сами по ссылке — московская онлайн школа https://shkola-onlajn-lzn.ru Хватит мучить себя и ребёнка Перешлите другим родителям
Народ у кого дети Дневники эти вечные Одни оценки и бесконечные поборы Короче, нашли отличный выход — школы дистанционного обучения с индивидуальным подходом Уроки в комфортное время В общем, там программа и условия — интернет-школа интернет-школа Переходите на нормальное обучение Перешлите другим родителям