Is there a way to control the population similar to terrain shaders? Specifically, I want to prevent my trees from growing on the mountain top or out of an 80° slope.
Couldn't find anything that does that, but I'm sure it's there, somewhere.
Plenty of different ways to do it, but the simplest to start with would be to create a surface layer, adjust the min/max height and slope you want and then plug that shader into the "use density shader" field in the population dialog box.
Ok, so I create a surface shader, but unlink it from actually affecting the surface rendering and instead plug it into the tree population?
Or, alternatively, could I just use some surface shader that already has the constraints I want (e.g. the grass shader) ?
Right - inside the population-node you can choose the planet and the shader, with which the populations is related to.
So any distribution-shader (itself) or surface-shader, etc. can be used the way RArcher was pointing to.
That's correct, Falcon. Distribution shaders need not be linked up in the main scene settings. An already existing surface works too, yes, so you could use your grass layer.
Just make sure the distribution node/shader is in the density input and that the 'blend by shader' box is also ticked in the population.
Ahh, Volker! You beat me by a few seconds. :)