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lava flow question

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hi,

i need to fill a street with lava that is moving in one direction (plz see attached). To make the lava flow across the road and given the street is level, how should I do that? One solution is to adjust particles velocity in each frame (i.e. blend v such that on each frame 10% desired velocity, 90% existing velocity), would that work? if not, any other idea? I thought making the floor inclined or changing the gravity direction, but that would cause possible issues ....

 

thx

lava_question.png

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Hi!

 If you don't want to change gravity direction, I think an inclined plane can work, or you can try to use POP force or POP wind to push your Flip.

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also a force node would work good here .... thx :)

force_node.png

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Another question regarding Lava, in the attached image below, the volume shape of the fluid indicates its high viscosity. Now my question: I have a large pool of Lava with many shots, and each shot is like 1 or 2 seconds, if I want to produce these viscous shapes, then I need to have super long preroll to make the sim naturally produce this viscous shapes per shot...Is this is the right way to go? Are there any cheats where I can give this viscous volume illusion without simming for so many frames?

Thx

lava_shape1.png

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What if you constructed a single longer lava flow to generate surfaced .bgeo files? Then grab a surfaced frame from that lava flow as the mesh populator for the shorter shots.

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17 hours ago, Atom said:

What if you constructed a single longer lava flow to generate surfaced .bgeo files

Thx :) My question here is : is there any other way to generate an initial (e.g. one frame only) convincing lava flow shape other than simming a heavy viscous fluid for so many frames? I am talking only about the first frame? this way each shot can have its own preroll and just sim for couple frames for that shot. 

Thank you ...

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I guess my point is that lava doesn't have to be a heavy sim. The example file on Houdini Blue print simulates fairly quickly.

https://hdbp.io/fK0FtieT

The detail in a lava shot is going to lean more on the materials rather than the surface generation.

Edited by Atom
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Thx Atom :) Yup, I was able to generate the sim easily as you mentioned, thx a lot. 

On 9/28/2021 at 10:45 AM, Atom said:

The detail in a lava shot is going to lean more on the materials rather than the surface generation.

We are using an external renderer, so we develop the shader ourselves. I would need to enable rest/rest2 to get UVs  on the Lava, right? If there is an article or a tutorial that discusses the general concept plz share it :) thx again :)

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Posted (edited)

Yes, you'd want to enable rest coordinates in order to have your texture coordinates stick to the lava for shader use; there is likely an example of using it somewhere onodforce, (I recall @Atom had one with a melting phone screen awhile back) and you can check out @toadstorm's overview of the overall concept on his blog  https://www.toadstorm.com/blog/?p=312 

In the case of lava, I don't believe you'd need full dual rest since the texture stretches by nature (someone please jump in and correct me if I'm mistaken) but worst-case you could have both enabled for safety and delete unwanted data in post.

Edit: With regards to previous conversation about generating initial frames without sim; remember the FLIP sim in the end is merely a large point cloud which can be generated from any geometry input; given that the surface and shading of lava is at its simplest a lot of overlapped noise functions, you should be able to model the shapes you want and apply an appropriate texture prior to their input into the FLIP solver.

Edited by ryew
other info
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8 hours ago, ryew said:

I don't believe you'd need full dual rest since the texture stretches by nature (someone please jump in and correct me if I'm mistaken)

I would say dual rest is quite useful. as stated previously by Atom a lot of the details you want will come from good shading and texturing. Dual rest will help you maintain a crisp look of your bump/ displacement on the surface

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Thanks for the tip, @Jesper Rahlff - do you have any recent simple examples of this you could post to demonstrate?  The H15 example mentioned in Houdini Blueprints is not using any rest coordinates and I've only used dual rest for Pyro texturing with single rest for melting/stretching FLIP so am unaware of the typical use there. 

I did find an old post by @toadstorm again here https://www.toadstorm.com/blog/?p=312 but it's 7 years back and a lot has changed since then so perhaps there is a more direct way to implement it now. 

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FLIP comes with built-in options for dual rest fields now... they've been there for a few years. My post is really old, but the concept behind dual rest fields hasn't changed... it's actually pretty similar to how flow map shaders work, if you're into shaders. You can find the options under Particle Motion > Rest on the FLIP Solver DOP.

Edited by toadstorm
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It's not much different from using single rest fields, just in addition of that you have to consider the interpolation between the two rest fields and their resets. To interpolate two details attribute are created by the solver. They are called rest_ratio and rest2_ratio, which are basically values that describe how much the noise advected by rest1 and the noise advected by rest2 should be visible at a certain frame.

 

About that, I think it's better you use higher values on "Frames between resets" on the Rest tab of the flip solver. Since usually it has to move slowly, you don't want to see any fast changing noise on the shader.

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attached is an example of how it could be done. Keep in mind this is intended to be used with lower contrast images, for bump mapping etc and not a fully blown high contrast brick image. but it gets the point across I think.

restratio_flipblend.hiplcblendRest.thumb.gif.50c309fb35064109d5363186cb9158a9.gif

Edited by Jesper Rahlff
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WOW, thaaaaaaaaaaanks everyone and special thanks Jesper :)

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Fantasic, thank you for providing some educational reference, Jesper!  I really appreciate it, looking forward to checking this out :)

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On 2021/10/12 at PM5点45分, Jesper Rahlff said:

附件是如何做到的一个例子。请记住,这旨在与低对比度图像、凹凸贴图等一起使用,而不是完全高对比度的砖块图像。但我认为这很重要。

restratio_flipblend.hiplcblendRest.thumb.gif.50c309fb35064109d5363186cb9158a9.gif

How to give mesh a correct UV use this method. Thank

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