Details on boiling water scene

[ben_hamburg]

Hi there,

I found another reason to squeeze in some phoenix into a shot, yay!
Beforehand: we are on nightly build revision 25960.
I want to use the boiling water scene as a starting point ( https://vimeo.com/78343279 ), but I could use some additional info:

1. In addition to using "foam" in the phoenix source as particle type, do I also have to enable the foam and/or mist/splashes in the simulator? Because I just simmed a couple of frames without foam enabled in the simulator and no foam seems to be created.
2. Am I correctly assuming that I also have to uncheck "solid" in the source objects phoenix properties and set the source to "inject" mode?
3. I´m not sure about the lifespan of the foam particles in the source helper. The default is something like 10000, is that supposed to be in seconds? That seems a bit excessive...Because in the video description you say you set the lifespan to something waaaay shorter (something like 0.01 sec). And also how does the lifespan variation work? Is the number you can punch in there a percentage or an absolute time?
4. I´m using the open boundaries option, but the liquid seems to react to the borders of the grid, as if they were jammed, am I doing something wrong here or is this a flip solver limitation right now? Because that doesn´t seem to happen in the video.
5. Also I noticed a new option there that says "confine geometry"? What exactly does that mean?
6. Does Phoenix "recognize" the scene scale? My scene is in meters (grid size is about 7x7x1m) and the default values seem to reflect that (0.3m for the foam size for example, also rise speed defaults to 10m).

Thats all I could think of right now, I would love to hear some input!

[Ivaylo Katev]

1. yes, you have to enable the foam
2. this is actually not important, you can use all type of sources
3. the lifespan of the source is ignored, the halflife of the foam is the important one.
4. better use the old core for this scene, because the "vary" option of the foam half life is not supported yet, and it is very very important for this scene
5. it's not a new, it's the old option called "gizmo", just renamed. the "gizmo" name was used by analogy with the atmosphere gizmo objects, but we decided that the word can be misleading
6. all the size parameters have constant initial values in scene units, this means they will change if the general scene scale is changed, but not if the container is changed

[ben_hamburg]

1. yes, you have to enable the foam

Yeah, I already got it working.

2. this is actually not important, you can use all type of sources

But doesn´t the "solid" option need to be unchecked, because otherwise the liquid would collide with the source object?

3. the lifespan of the source is ignored, the halflife of the foam is the important one.

Ok. Is the lifespan always ignored, or just for foam particles?

4. better use the old core for this scene, because the "vary" option of the foam half life is not supported yet, and it is very very important for this scene

I see, I didn´t know this, since the vary option was there with the flip solver aswell...

5. it's not a new, it's the old option called "gizmo", just renamed. the "gizmo" name was used by analogy with the atmosphere gizmo objects, but we decided that the word can be misleading

Ok. So it just acts as a rendering gizmo, right?
Thats a pity...I was hoping it was an easier way to simulate liquids inside an object (like a winebottle), that would let me skip the initial fillup process...(discharge at 100...and then wait 200 frames to settle)....

6. all the size parameters have constant initial values in scene units, this means they will change if the general scene scale is changed, but not if the container is changed

Ok, that s good to hear, makes total sense, otherwise one would have to adjust all values by hand, if simulating in another scene scale than the defaullt...

[Ivaylo Katev]

about question 2, the re is no difference between solid and non solid object with inject mode, in both the cases the liquid will be pushed out and beside the foam you will have liquid movement too. the non solid brush source mode will produce different effect, there will be no liquid movement, only the foam makes the trick. in this scene water is moving, so it's inject or solid source, can't remember which one

[ben_hamburg]

Alright, everything looks good so far, but while testrendering I noticed that the render times are going through the roof when I enable foam.
I usually rendered foam in point mode and could easily render it in an extra pass, but with bubbles I´m not sure that will work.
I´d think it would be fine, if the bubbles would only have specular highlights and not actually trace reflections, but there is no such option.
Also they would still be refractive, so that will add to render times anyways.
Any other advice on rendering the foam?

Does the disabling of liquid shadows have any significant impact?
And how would I go about rendering in passes- render one layer with everything visible , but only bubbles below water, then render an extra foam layer with only bubbles above water?

[Ivaylo Katev]

with closeup bubbles you have to render in one pass.
but they are not big in count are they? how many bubbles you have?
you can disable the reflection/ refraction by the option bounces, in this case the environment map slot will be used as fake reflection.

[ben_hamburg]

Ok, I´ll try disabling the bounces.
I have around 50.000 foam particles.
Might be better to reduce the foam brith rate and increase the size of the bubbles in my case, since they are not super close.