Hi guys. I've just started using Houdini a week ago and I'm playing with the pyroFX Flame system. But the flames and smoke i've gotten so far are a bit blurry and vague.

can anyone tell me what's going on???

Hey,

you referring to the render quality or the overall look of the flames?

eitht.

overall look of the flame.

Lainne

You may want to increase the resolution of your fluid container it will help a lot

Nothing to do with the resolution of the fluid container. Since the volume is well defined and continuous throughout the volume, you should be able to get a fairly crisp outline on any volume, period. Actually to the point where aliasing becomes the issue and then back off on the sharpness.

It's all in the Pyro shader and it being set up to basic defaults to give you something decent given all the variables that exist in a pyro combustion simulation.

What is causing the most amount of softness is the fire color ramp on the Pyro shader set up for you from the shelf. The first key is set to 0,0,0 (black) and then ramps up to the first color somewhere in the middle of the color ramp along with the minimum fire index value set to 0. This soft ramp -in is what is causing the softness.

If you change the color ramp's first key in the Color tab to say a red from the default black while running an ipr render, you will see the fire render gets a lot larger as you are now rendering the entire temperature Source Range. Then go to the Density tab and change the Source Range min value to say 0.9 to clamp out the temperature field start in range.
There's your sharp edge.
Now you have a sharper leading edge to your fire. The closer those two first keys are, the sharper the edge. Careful as if they get too close together, you may get aliasing on the edge.
Next set the Source Range maximum value to 6.5 to render the ramp against the full temperature range.

You can also enable the Contour option in the Fire > Density tab to add further sharpening to the edge. Again watch out for aliasing.

Finally you can manipulate the fire density ramp so that you create almost a box filter over the first part of the ramp. That is two keys to begin, one at 0.0001 in and the second at 0.01 in, then another couple keys fairly close together starting at say 0.15 and 0.05 units apart and then slide the two last keys around until you get the fire folds you want in your render.


Because every pyro simulation can have wildly varying temperature ranges, the default is to pick up temperature from 0-1 and do the remapping in the color ramp in order to give you a decent result no matter what you feed it.



What's the Temperature Range?
Why this? Because by default the Pyro shader uses the temperature field range to map in to the density ramp and the color ramp for the fire. This defaults to 0-1 but if your temperature field goes from 0-6, you are clipping a lot of the temperature field to 1. That's fine in itself but not if you don't understand “why” you want it set at 1.

The first thing to do is to figure out what the temperature range is in your simulation. You can use the visualization min and max range values on the Smoke Object DOP to see what temperatures you are dealing with while watching the temperature Visualization guide geometry in the viewport.

In your simulation, using using the XCF ladder on the temperature Guide Range max parameter while visualizing temperature visualization (temporarily turning off the Multi Field display), I increase the value until the white is just about to disappear. This allows you to see the ramp spread across the entire temperature field. I get a max value of around 6.5. I like doing this visually as opposed to using the two hscript functions volumemin() and volumemax() (the more techy guys will quip on this but it doesn't matter) because you can see where the more interesting values are as you use the XCF ladder handle.

Once you have your temperature range, go to the Pyro shader and follow the steps in the answer above. Now you know why you want to set the color range to have color all the way across and why you want to remap the temperature coming in from 0.9 to 6.5 to 0-1 to feed the density ramp and color ramp accordingly. Control.

With this you have complete control over what folds in the fire you want to bring out and how bright those folds are by manipulating the temperature in min-max ranges, the density ramp and the color ramp.


In practice it takes longer to add the keys in the Pyro shader's color ramp than it does to figure out what the temperature range is and fine tune the Pyro shader.

i'll test that out. thanks jeff!

hey Jeff.sorry.need to ask another question.

so the correct workflow is adjust behavior of fire in the pyrosolver then the temperature range and finally the colour ramp?

Exactly.

The first goal is to create an interesting simulation with the character you want. The min and max ranges of many of the fields may not be where all the interesting stuff happens. Just take a look at the temperature field. The interesting folds in that field are generally inside and not at 0.

Velocity is everything so I always have the visualization for vel on when running pyro sims along with other fields in the viewport. I always pop a floating pane on the Smoke Object DOP with the toggles for turning on-off various visualization options to see what's going on. Great for debugging things.

Once the sim is looking interesting, you go to either the Visualization settings or the Pyro shader and start messing with the min and max ranges on the fields you are using as control fields. For Pyro flames, it's temperature for the fire.

Then you go to the color ramp and start working on what colours you want within the narrow band of temperature for flames.

sorry.need a little more help ops: .

i'm tryin to get the fire more streaky n separated(i've place collision for my firewood but the fire just covered them n blob up again) instead of a big fire in the middle.I've seen other ppl's flames and they've got the streaky effect.

I've up the buoyancy level to 20 so it'll burn faster and turned the gas released down till 2 so tat it wouldn't blow side ways. I'm currently working only on dissipation disturbance and shredding.

Is there an extreme value that I shouldn't bypass because my fire will just break apart n blow everywhere. And in my viewport, it's all blobs!What's goin on?!

I'm thinking maybe my source object is too big to burn that's why I can't get the streak effect because all the fire is gluing itself to the source object?

oh and. How did you render out the smoke?all I've got are white pixels.

Too much questions in my head.

My memory tells me “Shredding” on the pyrosolver would help get the streaky look, I have not worked on flames often so I could be wrong… ><

edit: Also recently read that scene/object scales plays a part when performing POP/DOP simulations, I would try scaling up the source to see if it helps.

Good luck!

eitht.

I used shredding but it separated my flames into bits to flow up.hence I dare not put in too much of a value because I want it to be a continuous flow.


or should I be using pyro cluster instead to get the fire so it'll come out streaky and single?