View Full Version : Animation : Gras blowing in the wind

04 April 2003, 08:46 PM
Hi guys

Im workin with a model where there are some plants (grass) that must be moved by the wind. Well, the way I made that was:
I used soft selection to select the upper part of the grass, and then applied a flex modifier to that.
Then I linked to a wind space warp but nothing happens... I need some irregular effect for the grass movement (turbulent), and I cannot achieve the effect I need.

What could be happening? is it wrong?

Thanks guys. :wavey:

04 April 2003, 09:31 PM
Have you tried it without the flex mod?

I'm not familier with wind (legal R3 user), but suspect that the flex modifier is not working and that noise and wave types would work.

Let us know,



04 April 2003, 09:56 PM
The problem is that noise modify a lot the geometry, and some plants get distorted, and wave produces a very regular effect, not like in real world...

...that's the point. I've red in MAX help that wind can do that, but there's no explanation over there...

04 April 2003, 10:07 PM
Just try it without FLEX and let me know...



04 April 2003, 10:16 PM
if I don't use flex, what I have to use for the grass motion?
I've tried wave and noise, but I told you that is not the effect I need to get...

04 April 2003, 10:18 PM
Is there a way to achieve this with wind?

I animate
04 April 2003, 10:27 PM
Hi there, :wavey:

Would you mind posting your file and let me have a go at it? I think I know how to fix this but want to make sure before sticking my foot in my mouth

04 April 2003, 10:36 PM
Flex is for secondary motion,...

I don't want to piss you off but are you sure you have examined all the options with wave and noise space warps? Use wave to set the general amplitude of the effect and use noise to randomize it. Subtle phase settings etc...

Maybe you just need FLEX above the other warps?



04 April 2003, 10:57 PM
It should work with wind spacewarp, but is very uniform(althoug has turbulence control). I would instead use a better "windlike" spacewarp force, like blur's - BlurWind and RandomWalk - that you can get here.

And example of flex with wind ...

04 April 2003, 11:10 PM
Another thing worth trying is the free 'grass-o-matic' plugin, which comes with 'druid' (a tree generater which is not free).. The plugin can be downloaded from
Direct link : (

it is quite easy to set up and it has built-in wind dynamics.

good luck!

04 April 2003, 11:11 PM
Hey guys...

I animate: Im sorry but I don't have the file right here. It's in a machine I've got at home, so I cannot upload right now...

Ls3D: Maybe you're right. Of course Flex is for secondary motion, and I'll try combining the two modifiers. Maybe this way I can achieve a random look... thanks.

Reality 3D: Thanks a lot for your time pal.

And thanks all of you people.


04 April 2003, 05:55 AM
careful mixing of two ripple spacewarps (or wave), bound through a soft selection as you already have, and a weak animated noise space warp can give you completely realistic grass blowing in the wind which you can tweak as you like to perfection.

You want to eliminate most but not all of the curvature in the ripple space warps, so move their centers far from the area under the camera's scrutiny. Another good tip is to tip them at an angle to the surface of the hill that the grass rests on.

A good mix of these spacewarps will give you that wavefront of grass blowing one might see on a windy day, a dark line seeming to flow through the grass. It's quite nice.

also, if you want cheap grass geometry, make tufts of grass by cutting a single face into the sillouette of many blades of grass, duplicate this sillouette a few times, modifying each copy to be unique, this way you will fill up a lot of space with very few objects (each blade of grass might fill only a pixel or two, requiring hundreds of thousands of blades to give convincing results - too many objects, slow render time, etc). If you array these in a smart fashion, the effect can be as convincing as if you had hundreds of thousands of blades without the cost of all that geometry.

04 April 2003, 11:16 AM
Thanks Johnny. It works really good. Your tips are great. I achieve random movement mixing two space warps as you said with a little noise. :thumbsup:

:shrug: finally, it means that it is no possible combine flex with sub-object soft selections...

04 April 2003, 12:22 PM
As far as I know the flex-thing should work. Yes Flex is for secondary motion, but since it now supports spacewarps as well it should be able to take the wind-thing and apply that to the geometry.

Why specifically it doesn't work for you I don't know, I guess it could be possible that there's something technical preventing it from working like I think it would.. in any event, it would be a computationally heavy process, calculating Flex on a whole field of grass.. better off, imo, faking it like you've ended up doing.

If you really love an actual dynamic solution you could also give SimCloth a try. Again, I can't see why one would want do that in most cases involving motion of grass, but.. to each his own?

Oh and Reactor might be of help as well, it's FFD softbody technique could probably speed things up somewhat.

04 April 2003, 12:26 PM
Hi guys!
Im very interested to see your output johnny or fabrizzio! I had the same problem days before but I gave up because of sucking output quality or loooong render times for shaqhair plugin:thumbsdow

Could you post some max file or small avi, please? Iīm only interested in large scale scenes (grass field over hill, not "Bugīs Life" like close ups of grass blades).

Thank you for any effort in advance!


04 April 2003, 12:28 PM
Originally posted by gaggle
As far as I know the flex-thing should work. Yes Flex is for secondary motion, but since it now supports spacewarps as well it should be able to take the wind-thing and apply that to the geometry.

Originally posted by fabrizzzio

finally, it means that it is no possible combine flex with sub-object soft selections...

And example of flex with wind ...

04 April 2003, 12:30 PM
Gaggle: yep, I ve tried these methods with cloth sims but I couldnīt make it work! I know they write (ChaosGroup) its possible to make grass with SimCloth but nobody wrote how!?:thumbsdow One thing which I have discovered you have to use negative gravity so grass is not laying down...

04 April 2003, 04:59 PM
I wouldn't think you'd have to use negative gravity? I understand how one could come to that conclusion, but I would guesstimate that you can make the grass-objects stiff enough not to bend to the gravity? Or, specifically, not bend too much, as some wind coupled with gravity and a nice springiness of the grass should make for some nice movement.

That's all theory. I just.. don't see why it shouldn't be possible.

We are talking about something very computationally expensive though, egads.. maybe if you wanted the grass to react physically correct to, say, the foot of a character, or the likes?.. but even then there are ways to cheat ones way to such a result that I still say SimCloth and the likes has no place in large-fields-of-grass scenarios :)

04 April 2003, 10:46 PM
The problem with that kind of solution is that the grass is modified in its geometry level. When it is no grass, and what we need to animate are a little bit complex plants, it transforms in a chaos of geometry, and the plants loss the features that make us recognize like what they are: plants.

I don't know what kinda solution use the big companys for this kinda problem... :surprised

04 April 2003, 02:54 AM
For large scale scenes just use a level of detail solution, more grasslike geometry the closer you get to the camera and less grasslike geometry the farther away you get (perhaps using the contour of a hill with a green noise map or just a flat plane representing a hill with an image map of little green dots). From more than a hundred yards, one's eyes can't resolve the motion of even clumps of grass anyways, maybe -- if anything -- the larger wavefronts of wind on an entire hill surface might be resolved.

Use different motion solutions for different distances, if your camera is set on a rock surrounded by tall stalks or reeds, animate these plants individually as their individual motions will be apparant at such a small distance, probably using a list rotation controlling that has at least one noise controller. You probably will have to give a few bones to very close up objects to represent true bending of stalks and leaves. Save your group motion solutions for the groups of plants that are far enough away that you cannot possibley notice the motion of individual plants.

Also, most outdoor scenes involve overlapping planes of geography (ie: hills) so this allows you to split a scene up into fore, middle, and background layers and only work on one at a time, perhaps xrefing in for setup purposes simpler copies of the other layers. For close up scenes, there really is no way to get around using individual plant/grass geometry.

I don't see the need for a dynamics solution to the problem - isn't the amount of geometry necessary to represent an entire meadow computationally heavy enough? Besides, if you think about the motion of grass in the wind is it really logical (of course when it comes to the infinity of interactions in a physically acurate representation it is logical) but to your eye, it really just seems kind of random. Remember: KISS (Keep - It - Simple - Stupid).

If you wanted to use a dynamics system you'd have to have some accurate turbulence and twisting of wind forces in a fractal type of way (large waves make overall blowing, smaller ones cause random-like blowing of different clumps). I don't think max has accurate turbulence anyways and you wouldn't need it if you had it (above).

If you really want to make it convincing, stop posting, leave your computer, and go look at a real grassy hill undergoing real wind. Take good notes and pictures or video, recording what the waving grass looks like from 3 meters, 100 meters, and 100+ meters. Ask yourself if you notice how the wind affects the grass from far away and if you do, how apparant is it? Do you see individual blades and clumps blowing around or is what you see more reminiscent of patches of light green color changing to dark green randomly. Also take note of how much the grass moves in it's bending and how quickly changes take place. Make notes on small scall movements (random-like motion of small areas) and larger scall movements (waves of energy moving through the field- these are usually very rhythmic and wave-like).

my two cent.

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