Wild fire spread

[sant0s81]

Hello,

I wanna create a Wild Fire.

On youtube I found a video, that shows a nice animation (01:30):

I wonder, what would be a good technique, to get that kinda shape of the burning movement.

In Softimage I would use a weightmap that starts at a point and than spreads with a turbulence to get these soft edges on the fire front.

Is there something similar I could do in Houdini to control the burning?

Thx alot!

 

Edited March 2, 2020 by sant0s81

[konstantin magnus]

Hi Salomon,

@pclaes explains a sophisticated way of spreading based on a shortest path map that can take in weights: https://www.youtube.com/watch?v=pTfzxTod7n4

Have a look at minute 24:42 to get a preview.

 

[sant0s81]

@konstantin magnus

Thx, thats perfekt! Even with the fading out...

[Atom]

Yeah, that one is a nice setup.

[sant0s81]

Love that effect, works almost like a charme

I have another question.
Is there a way, to multiply the speed into one distance to kinda simulate wind?
 

Here is an example (only with a cheap shader and glow, no fire and smoke yet.
And there are still some jumps and strange flickering areas - but that I guess I can fix.

Cool would be to have a faster spreading to the right side.

Thx alot

 

[konstantin magnus]

You could fit range the dot product of the normalized wind direction and the spreading direction as a multiplier.

float angle = dot(dir_wind, dir_spread);
float angle_mod = fit(angle, -1.0, 1.0, speed_min, speed_max);

 

[sant0s81]

@konstantin magnus

I guess I asked wrong

At the moment, its spreading in all directions with the same speed.

But since wild fires often get pushed harder into one direction, I thought I could modify the spreading in Z+ quicker, than in Z- and X+ / X-.

I already got something that comes close. I multiplyed Z.
But of course it spreads quicker in both Z+ and Z- .

Is there a way, to spread in Z+ only but leave Z- the same speed than X+ / X- ?

 

[Howitzer99]

Magnus had a good idea with using dot products.  The dot product will give you a scalar to use as a multiplier for your wind.  If you take the positive value of the dot product, then this will only increase the spread in the direction of the wind, where the spread angle and the wind angle are in a similar direction.  Hopefully that makes sense.

[konstantin magnus]

@sant0s81 Use a compare node to check if Z is above 0.

Direction-wise you are more flexible with a dot product and a ramp, though.

wind.hipnc

[sant0s81]

Thx @konstantin magnus

gonna try that!

Really have to get into JoyOfVEX to understand more of its magic...
So cool stuff you can do.

[Atom]

Do you have any tips on how to adapt the point wind to the findshortestpath expansion from the tutorial?

Basically push the white color of the points in the wind direction, not the actual points themselves?

ap_find_shortest_path_wildfire_spread.hiplc

[konstantin magnus]

16 hours ago, Atom said:

Do you have any tips on how to adapt the point wind to the findshortestpath expansion from the tutorial?

You could feed the cost attribute into a measure node to calculate gradient vectors. Multiply the fit-ranged dot product on those vectors and subtract their length to the cost attribute.

Edited March 5, 2020 by konstantin magnus

[sant0s81]

Since I also dont get it to run with the findshortespath yet, I used a super cheap trick to get the spreading grow quicker in one direction...

In the group I used "Keep in Boundin Regions" and just animated the scale of the Bounding Box into the direction I need it to grow quicker

Cheap, but it does actually an amazing job, hehhe.

[pclaes]

Have you checked out the new Houdini 18 spreading fire setup? 
That thing kicks *ss! It is a solver so a little harder to control than shortest path and a little slower, but beautiful results for spreading fire. Worth checking out!
 

In sops -> from the tab menu -> Pyro -> Pyro Configure Spreading Fire

 

Shortest path requires connectivity, the Pyro Spreading fire can be configured to not require connectivity. -- It will jump gaps if the gaps are small enough.

Good luck!