explosion particle effects

Ged

Ive seen some really nice particle effects lately and Ive been trying to break down how they are done in my head but I thought I would discuss this topic with a wider audience

how would the explosions in this trailer for the new C&C game be made
http://www.youtube.com/watch?feature=player_embedded&v=kjZEInQZA0c

will they really look like that in game seems like it may just be CG composits? if it is in game how would it be done? is it perhaps very nicely animated textures applied to the individual particles or something like that?

LoTekK

Those explosions (at least the growing fireballs) look like they're using the fancypants dx11 technique nvidia described in a paper a while back, using tessellation and displacement, pyroclastic noise, and raymarching.

Unity showed off the technique working in realtime in the realtime short movie they showcased at Unite 2012, as well as in their DX11 features video:

[ame="http://www.youtube.com/watch?v=hCCaUa6p5mo"]Unity 4 - DirectX 11 Support - YouTube[/ame]

Smoke looks like standard particle smoke, though.

Ged

I have seen those videos but i just assumed that such an expensive effect would not be used very often but c&c proves me wrong! What about the explosions in just cause 2 they look pretty good and solid but they arent using 3d tesselation are they? ...i cant find the vid of just cause 2 right now but theres a good one where they set off hundreds of explosives at once.

LoTekK

Just Cause 2 I'm pretty sure just used straight up particles for their explosions. Good-looking particles and whatnot, but particles nonetheless.

Ged

so this is just particles...


they must be animated particles(as in each particle has an animation going from white hot to a smoke and flames combo to full on smoke at the end etc)? but there are some nice glows and hot parts coming through the smoke, its very effective. Also how can the particle smoke in this screenshot above not be covering the white hot glow at the origin of the explosion? surely it would cover it if it was just alpha blended smoke but somehow they have kept the warm glow on top of the smoke?

tharle

its a nice bit of interesting tech but i dont think they're using it in this game - think it's just normal flipbooking sprites. if you download it with something like keepvid.com and then frame by frame though it with vlc you can see repeats in the sprites which i wouldn't have expected with the noise technique from the video.

imo it's a couple of different textures made using FumeFX and then using a premultiplied blend mode. this allows them to start off with a bright glowing texture and then fade in the darks as the explosion grows. There's no doubting they're nicely made but i don't think there's any clever tech going on here.

Ged

Hey your stuff is pretty cool tharle! do you often use a flipbook flame particle and a flipbook smoke particle to create an explosion and then add debris effects? Im unfamiliar to the usage of premultiplied blend mode, how and when would a person use premultiplied particles to good effect? Im primarily a 3d artist/modeller but I've also been doing particle effects when given the chance.

tharle

cheers Ged, basically yeah - i pretty much use flipbooks for everything at work since we can't use animated materials on sprites like you can in UDK but that doesnt mean it's the only way to do it.

there's an explanation of premultiplied here: which is a little technical. basically it allows you to change from an additive blend mode to a masked one by controlling the alpha and the colour of the sprite:

High colour + low alpha = glowing
High colour + high alpha = half way between normal and glowing
Low colour + high alpha = normal
Low colour + low alpha = transparent

it works really well for explosions because you want to go from glowing to bring out the darks as the explosion ages.

Ged

thank you so much for that explanation! Ive just made a fantastic glowy premultiplied explosion! haha its a really useful technique!

What would you polycount people use for making explosion sprites? fumefx? I recommend TimelineFX for making explosion sprites on a budget but the results are actually pretty cool with a bit of editing! http://www.rigzsoft.co.uk/

tharle

yeah i use fume at work - it expensive and there's a relatively steep learning curve, not to mention you'll need a powerful computer, but it's the best thing for fire and smoke i've found.

LoTekK

So to clear that C&C bit up, a quote from one of the FX artists on the game:

Its just flipbook seq of images, our lighting method for particles is however very awesome that it even lured nvidia to believe they are volumetric particles we render

Ged

ah awesome info there thanks, maybe the secrets all in the particle shader and nice flipbook sequences then!

LoTekK

A little more:

Standard Frostbite 2 particle lighting and a flipbook. Each emitter that resides within an effect has a built in point light with an array of parameters for timing/rgb values/etc etc. It works extremely well when your using a normal map with the flipbook, allowing you to get that internal glow from the dissipating fuel as it's enveloped by smoke.

I also tend to find that punching the rgb values of the flipbook really high works well too in certain cases.

kio

nice thread so far! way too less info on cool fx stuff out there.

Ged

Oooo Lotekk that sounds awesome but now Im a bit confused. Surely its extremely performance intensive to have a point light in every particle emitter and an animated normal map in every particle plus a fancy shader that lights the normal map correctly? Also do you think they mean the individual particles where animated flipbook style with normals and then put together to look like a big explosion... or do they mean they animated the whole explosion as a flipbook with normals(they could do this because thier camera doesnt rotate around the explosion does it?)

Ged

so has anyone here had a go at making normal mapped particles or a normal mapped particle shader? its this tech we are discussing right? http://www.gamerendering.com/2009/09/15/normal-mapped-billboards/

JohnnyRaptor

that looks like particles with camera facing planes with a sphere normalmap

also, i think they mean they have a flipbook animation on the particles. and several emitters per explosion, to combine smoke, fire, debri etc.

Ged

yeah sure, I was just giving an example of that tech as a starting point. Ive noticed that even a simple sphere normal map in a particle emitter doesn't work for me in unity3d. when I use it with a particle system the specular seems to get set when the particle spawns but stays there even when the particle rotates and also the lighting in unity doesn't seem to work correctly and creates some weird artifacts when the camera moves around the particles. I may have to get a custom shader made.

JohnnyRaptor

sounds like they take lighting info on creation and thats it? maybe a setting on the emitter to allow dynamic lighting?