Need a little help with a grass technique

Hey everyone,

I Need a bit of help finding a way to implement a technique in blender that I originally developed in max.

The context is wanting to put grass on a large terrain mesh. In max I used particle flow to scatter little grass billboards over the terrain automatically. The problem I ran into (predictably) was that the amount of grass that was required to give nice coverage when applied to the entire terrain was too much for a non supercomputer.

The solution I developed in max (without out getting into the gory details) was to put - and link - a large invisible sphere in front of my camera. Then I did a few tricky things to tell particle flow to only put grass billboards on the terrain where the sphere was intersecting. So grass was only spawned within a certain range of the camera (determined by the size of the sphere).

Now the blender bit. First of all, the new hair stuff is UTTERLY amazing, I couldn’t express enough thanks to the guys who have made this happen. You’ve set me free man :o)

So the thing with the new particle stuff is that it also does great looking grass, but runs into the same issues max did. When I saw a page at the blender site talking about texture based emission of particles, I remembered a tute by theeth about doing decals (using an empty to control the placement of an image on another objects surface) and got all excited about using an empty linked to a camera to control a blend (sphere) texture on my terrain that would control the emission of my grass. Alas, texture based emission appears to not be implemented for static particles.

So, how to make it work? Either it will be somehow making blender make a vertex group in an object based on one of it’s textures, or it will be making blender update an objects vertex group based on how much another object is intersecting it. But I don’t know enough about blender yet to figure this out, can anyone offer any suggestions?

P.S. If someone can help me figure this out, I’ll be more than happy to do a big tutorial showing everyone how to do it.

Thanks,
Simon O

Alas, texture based emission appears to not be implemented for static particles.

http://tinypic.com/i7955s.jpg

What’s this thing then?

Edit: Hmm… wait, it doesn’t appear to work.
I am the wrong person to try to solve your problems about static particles. I never should have spoken.

Hey,

thanks, but I’ve already tried that …

(https://blenderartists.org/forum/viewtopic.php?t=55922)

It doesn’t seem to work for static particles.

Here’s a link to my blend file again, maybe it’s just me doing something wrong?

http://www.ultramedia.com.au/hair_texture_emission.blend

Thanks,
Simon O

btw, here’s a sample shot of my cat mech in blender grass…

(the tail is sticking straight out because the mech is not rigged yet)

http://www.ultramedia.com.au/blenders/mech_08_01.jpg

Link is dead.

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Hey Fligh,

Hmmm… I can see it in the post at my end…

Have you got a dead link on the image and the blend file?
Also are you able to access my website at http://www.ultramedia.com.au ?

(I had a friend in france who couldn’t access my site from home, but could from work)

Your server must have been dead 10 min ago cuz I couldn’t see your pic either, now I can.

Just add the texture to the 8th slot in F6. Play around with different (monochrome) procedurals to see different effects (clouds marble etc)

http://blender.isoserv.com/uploads/hair_texture_emission1.blend

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try searching this forum for grass fibre/fiber duplivert

there is a method of making grass with a fiber script i dont know if i have it now.

and there is also a method using dupliverts.

ouch… damn, I’m such an idiot, it’s been right in front of me all the time…

just use a single curve guide set to additive. That way ‘grass grows’ inside the maxdist of the curve guide, and outside it doesn’t - allowing you to focus your particle count in a specific area (i.e. around the camera)

will try and get some sort of tute done on the weekend

One thing though, and this might be a bug/feature of the particle system, if I put a value in random under particle motion, I get scrappy bits of particle ‘grass’ over my entire mesh outside of the maxdist on the curve guide… any ideas?

Thanks,
Simon O

if I put a value in random under particle motion, I get scrappy bits of particle ‘grass’ over my entire mesh outside of the maxdist on the curve guide

What’s your definition of Random them, Gov?

allowing you to focus your particle count in a specific area

You can also use WeightPainting and Vertex Groups.

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I’m trying to create a system where you can have a camera flying over a large terrain mesh, and the particle system creates a nice looking area of grass only on the parts of the mesh that are near the camera.

Here’s my blend so far:
http://www.ultramedia.com.au/blenders/canyon_01.blend

You can see that blender can’t do enough particles to give dense coverage over the entire mesh, and it would be overkill anyway, I’ve put a curve guide in near the cat, in my previous post I hoped that would cause the particle count to be clustered in that area. Unfortunately as you can see in the file, the count is still spread over the whole mesh, it’s just the growth that is clustered around the curve guide :o(

Also I don’t think vertex painting is the answer because I don’t know how to make it follow the camera.

Sorry about not explaining it very well, hopefully seeing the file will make it easier to see what I’m trying to achieve…

Simon O

If I were you I’d learn to use the Sequence Editor. Bite the bullet and render the topography with all the grass to a sequence of .png’s thru the camera. Then do the same, using the same camera to render the object(s) and animation. Put them together in the SE.

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