View Full Version : particles as grass

11-11-2004, 03:10 PM
hi, ive tried hair- theres a prob with shadowing and the effect looks toon rendered which mings.
so ive used an instanced group of grass blade with particles to cover a field. now i want to animate the field- apply a force to it- and its not working.
is there anyway i can animate it?


11-12-2004, 01:08 AM
Instances probably aren't the way to go if you want to animate the blades - they don't really have geometry to deform - they're always going to copy the master's shape.

In terms of the hair, were you using the regular hair shader or the geometry hair shader? What was the problem with the shadows... and what's a ming anyways?

11-12-2004, 09:59 AM
ming is short for minging, which means 'looks bad'. a minging girl is an ugly one.
i used the regular shader and also tried the muh hair shader, and both seem to render the grass in either one tone or two tone colour. i want the look of shaded geometry (im using fgs too), but with the ability to be animated gently in the wind.

heres a couple of images...

hair... minging!


if i can get the geometry look for hair then ill use that...

11-12-2004, 07:32 PM
Hmmm... Played around with this awhile today. Tried the Geometry Hair Shader with transparency off and it can get close, but it's not easy to get an even lighting feel. Tried playing around with Scalar State nodes set to hair lengthwise and crosswise but didn't get anything too promising. And if you plug a blinn or lambert into the hair, it loses the illusion of roundness (maybe I should have spent more time with a scalar set to crosswise to get that roundness...)

Anyways, I'm guessing that the camera shot you showed is one of the more forgiving in your piece. Because from that angle, it wouldn't be too heavy to do it with straight geometry... maybe some low rez poly meshes deformed along 4 points curves, then a few overlapping wave deformers on the splines to create the wind. But naturally, I'm sure the camera's going to pan up over a sea of grass... :P

Someday soon I hope we'll be able to use hair guides as deformers with relative ease... it's annoying having dynamics right there for us to use, but you have to go through a lot of hoops (nulls to clusters mostly) to get those guides to work for anything other than hair.

Hmmm... not much help there, maybe someone else has an idea.

11-12-2004, 09:40 PM
I did a test maybe it fits your needs. When using hair for closeups don't use geometry since it uses flat "polys" as hair primitives, so you lose the ilussion of a 3d shape. It is indeed geometry but planar geometry. So volume works better in this case. The trick is to turn off transparency as Ablefish suggested, but I also turned the normal blend to 1, the shading is completly different that way, it looks more 3d and respects ambient/diffuse ratio much better. The only bad thing about volume is that steps are much more noticeable than geometry hair, so I had to increase steps way up.
Here is a pic.

Hope this helps. ( not perfect though )
P.S. the placement of my hairs looks "minging" :) but i was just testing shading so many hairs overlap.

EDIT: one thing to remember when using volume hair is that you can't use shadow maps nor dirtmap shader, or any other shader wich computes from geometry boundaries since volumes will throw a bounding box to the calculation and will mess the illusion. But you can use raytraced shadows or even area lights if you need soft shadows ( or even better render your shadows in another pass so you can blur them in post and get faster rendertimes)

11-14-2004, 12:09 PM
ah yeah. thats very close, ill give it a try.
its a shame you cant freeze the particles then apply cloned geometry to the particles from the original model. then you could apply a force...
but the hair looks good.
thanks guys.

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