It's an impressive effect for sure. When I first saw it, my first inclination was that it was bullshot footage, prerendered to wow the audience. But as soon as other footage cropped up I understood exactly how they did it.
The entire explosion is one big 2D facade. A flat plane with an animation rendered out from a fluid simulation program. It's more or less a high res version of the explosion sprites from Duke Nukem.
Now I typically wouldn't have too much of a problem with this. Several other games have used similar techniques to achieve impressive visuals for cheap.
However, my issue with BF4's usage of the technique is the fact that if you get too close to it, you start to see the man behind the curtain. If it were something off in the background, or something that you could only ever look at from one perspective, then it'd work great. But like I showed in that video above, if you walk right up to it the effect is completely ruined. They are attempting to use prerendered simulations in places where traditional particle systems should normally be used.
With the rise of fluid simulators, and the ability to render out spectacular looking effects, it feels like people are trying to use these animations to do all the work for them.
For those who don't know, a fluid simulator is a program like FumeFX, Maya Fluids, or PhoenixFD, that is able to create a 3D simulation of fluid dynamics, meaning that you can use them to create fairly accurate simulations of fire, smoke, and water. You typically see 3D simulated effects in movies, where doing the effect practically would be too expensive.
Plenty of fluid sim action in this reel.
So the question is, now that we have fluid sim technology, why should you bother creating a complex particle system when you can render out a 2D animation of something and have that be the entire effect?
Because relying on a fluid sim means that you're taking away a lot of your own style from your effects. When you have to come up with your own way to animated fire, smoke, dust, debris, you inject a lot of your own personal vision into how it looks. But if you let the computer simulate it all for you, it winds up feeling soulless and homogenized.
Compare the fire graphics of Far Cry 2 and Far Cry 3. FC3 used fluid simmed textures for the majority of it's effects. Personally I preferred FC2's fire, as it feels like the the action is more in the way the particles were actually moving, rather than just relying on the animation of the texture.
My other issue with fluid sims is that they tend to feel the same, and they never look quite right.
Two different reels by two different people, but since they both used the same fluid sim, it all winds up looking samey.
Fluid sim FX have a certain look to them. A look that we've come to learn through their usage in movies. When we see CGI in movies, it typically sticks out like a sore thumb, so our brain associates the look of it with 'fakeness'. This carries over to when we see that same look in videogames. Even though the rest of the game environment is fake as well, seeing the familiar look of fluid simmed effects triggers the same fakeness vibe we get when seeing them in movies.
So I know I've been harping on fluid simulators this entire post, so I must think they're awful things that shouldn't ever be used.
Well not exactly. Fluid simulators CAN be very useful tools, if used in moderation. If you can mix together fluid simmed textures along with more traditiona techniques, you can give your effects much more naturalistic motion.
My only concern for the future is if we ever make fluid simulations that run in real time. If that becomes mainstream it may mean the phasing out of traditional sprite-based particle effects. What makes VFX so varied and unique in games is the limitations imposed on the FX artists. If we remove those limitations and replace it with systems that create the art for you, we could lose a lot of what makes VFX so great.