Limiting populations to specific surface shaders?

[mrwho]

I want to place a forest population, but limited to one surface layer. It's (the surface layer) is green, and is elevation and surface angle controlled. How would I have a population show up only on that surface layer?

[duff]

You can use the output of the surface layer to be the density shader in the population distribution.

[mrwho]

I tried that earlier, but it didn't cover the entire surface layer, no matter how large I made the population

[bigben]

OK this is a basic approach (not the only way), and it can get a little complicated (or simplified) depending on your surface settings.

Create a duplicate white surface layer using the same coverage, fractal density and other restrictions as your reference surface. Plug the fractal breakup from your reference surface into your duplicate surface. Use the duplicate surface as the density shader for your population.

[attachthumb=#2]

If you use your green surface, the max pixel value in the channel used for masking (probably blue) will be lower than what your are requiring.

As an extra level of control, I'd also run your duplicate shader through a colour adjust shader (just noticed the English spelling of colour... excellent ) to tweak the actual density of objects to what you want.

[mrwho]

thanks ben, I'll try that

[Aenea]

Hi BigBen!

A wonderful question from mrwho. I tried your tip too, but haven´t succeeded so far....

I´m at the moment not quite sure if you need the area distriction too and/or if I made a mistake in my node networking (based on your example. Currently without the colour adjust shader....cause I really don´t know why/how to use it...maybe you can explain that a little bit more? Would be so kind....)

And also it would be interesting to get behind the secret of getting this population on the surface....

In my case I have a grass layer where I want to put gras clumps to....allover it....
So it´s an interesting question how to do that...without getting gras into my little river and the river bank...think this can be normally done with a distribution shader...but can´t I just use this second gras layer as density shader OR the dsitribution shader? Dunno....
I hope someone understands my little problem....the tgd is in the attachment....just in case

thanks

Aenea

[bigben]

You have a few fractal breakups that don't actually do anything because the coverage of the layers they're connected to = 1.

Assuming you want to replace the image-mapped grass surface with an object population, then all you need is a white surface shader with the same altitude constraints as the grass surface as the density shader of the population. (attached clip file)

[Aenea]

hmmmmm

I tried it but it doesn´t work yet....dunno why.....no population appears

Aenea

[Aenea]

I succeeded by using a distribution shader with the population....

but it would be still interesting this other way....

Aenea