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Comment by Notatheist | Hacker News Reader

Making a realistic CG fire isn't hard. I can (and do) do it by myself on my home desktop. Making a realistic CG fire for a complex hollywood production is practically impossible because:

>Friedlander notes that the fire scene in No Hard Feelings was part of reshoots that took place just a month and change before the film hit theaters — giving the effects team only a couple of weeks to work.

Literally the only reason. I'll bet you anything that team didn't have a few weeks. More like hours. A set has to be built, cameras transported, crew flown in. That overhead is accounted for. CG is considered a bunch 1s and 0s we can conjure from thin air with a few clicks. Bad directors expect miracles, don't get them, then scream "CG BAD!".

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A lot of times you will not do the fire in 3D, but you just in compositing by adding fire from one of your thousand movie libraries. The problem of course is that you can do that and it might even look good if you match the angle, but you will have a hard time lighting the scene probably, and faking all reflections in.

As someone who worked as a camera person I want to emphasize another aspect: Shooting the real thing (fire) is itself not without its challenges. You really need to match light levels well or else you won't even notice fire in the picture. Fire doesn't always burn in visually pleasing ways, and especially outside wind can make or break how it will look.

You’re right the VFX is often rushed and under budgeted. However realistic fire IS really hard and frankly I’m sceptical you can do it yourself on your desktop. On its own on a plain background, maybe. The moment you comp it in to a live plate our uncanny valley spidey senses kick in — to take it beyond “looks good” to “oh, I didn’t notice that was a VFX element” is still REALLY tough in many situations.

sceptical

(skeptical)

Fire is a fluid simulation and this has been in consumer tools like houdini for a long time now. Even in avatar from 14 years ago there were plenty of CG explosions that people didn't think about.

The moment you comp it in to a live plate our uncanny valley spidey senses kick in

I haven't seen this be the case if the scale is right and the resolution is good. After that it is a matter of compositing. There is actually a decent amount of cg fire out there now. I found this after 10 seconds of searching on youtube:

https://www.youtube.com/watch?v=1Ec3hrkwh8Q

Doing live action integration is tough in general, but fire is additive and that helps quite a bit. LEDs that can be add lighting to the photography helps too.

Sceptical (I’m English).

And, I realise. I first learned Houdini c. 2004 so I’m aware of the technology.

Your YouTube link is a perfect example. It looks good but certainly doesn’t pass the bar for mistake-it-for-the-real-thing realism.

It's easy to say when it's a full resolution demo on a black background and you know it's fake, but sprinkled into a live action shot and I don't think people notice. This is already something that is being done all the time.

Also houdini in 2004 didn't have anything like the fluid simulations it has now.

> Making a realistic CG fire isn't hard. I can (and do) do it by myself on my home desktop.

Can you really? On the clothing of a human body that's in motion in a strong wind? That accurately illuminates that human and the environment around them? And the fire and illuminated objects are all properly reflected on adjacent shiny surfaces like car window and car hood?

Because that's the scenario presented at the very top of the article. And it does indeed sound dastardly difficult. Or while it's maybe possible with enough painstaking work, it's difficult enough that no movie would ever have a large enough budget for it. (Although I really do wonder if we have accurate enough physics models of the igniting gases to truly realistically show the way licks of flames ignite in a strong wind -- as opposed to a more bog-standard campfire type.)

I disagree for the need for complete physical accuracy. The illusion of accuracy can be equally as strong in film. Film has always been about creating successful illusions. But figuring out how to create the illusion for a specific shot takes an experienced artist time. Time they are rarely given these days and aren't being paid enough to do.

I think OP is saying he has that freedom and time to do exactly that on his desktop.

But the article is about so many examples of unsuccessful illusions. So that's what I'm questioning: do we really have the technical ability to create realistic-enough fire in these types of complex scenarios? Even given a reasonable but realistic timeframe?

Just because we can easily make realistic-enough fire in some scenarios doesn't mean we can in all. And clothing on fire on a human body in motion in the wind sounds like one of the hardest scenarios of all.

Yes, but you won't see it often because VFX artists aren't paid what they're worth, are given unrealistic timeframes, and are even given sloppy direction that is counter to what a realistic effect should look like.

Sorry I'm late.

I wasn't saying all they needed to do to get perfectly realistic fire in all scenarios is hire one guy with a 1950x. Our pipeline still ends on a supercomputer. I'm saying if you see a garbage fire in a film you don't need to write an article about "why fire hard". The answer is "they were unwilling to pay for a realistic fire". We're not talking billions of dollars here. Not everything is Avatar. But like I said, studios often expect miracles for little to no money. Fire isn't like skin/faces which is actually genuinely ridiculously hard to pull off.

>Although I really do wonder if we have accurate enough physics models of the igniting gases to truly realistically show the way licks of flames ignite in a strong wind -- as opposed to a more bog-standard campfire type

That would make an excellent article because you don't actually want a "realistic" fire. Don't forget we're doing entertainment, not science. Turbulence in media is just a noise function. I want a pretty vector field visual to indicate where and how my sim will move. Pyrotechnics is the same. We want control. Realism is undesirable. It's like asking for realistic silencers. John Wick is amazing because the silencers aren't realistic. The explosions and fires you see in film/tv aren't functionally realistic (though manipulated to appear so) and that's a good thing.

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