Emit particles depending on slope of terrain

[richard-stevenson--3]

this could be used to emit instances from a terrain and cull the particles that emit from steep slopes.

What I'm thinking is that

1:     at particle birth position, sample the normal direction of the terrain surface.

2:     if the angle of the normal direction is greater than the angle threshhold then lifespanPP of particle  = 0

I'm still a novice at Mel scripting but I think that this could be really useful for large terrains.
any help would be much appreciated!
Cheers

edit:

I've tried using the sampler info node to generate a black and white mask and plugging that into the particle emission but can't get the sampler node's facingRatio to link to the top camera to generate the mask

[joojaa]

Theres is a per vertex/texture emission rate available so you donbt actually need any of the steps you describe.

[peter-hunt--2]

This is in python, but I did something fairly similar before for my uni assignement. It doesn't emit particles based on the slope, but it can figure out which particles are on the slope

Basically, it fires particles out, looks at the speed, and can figure out the slope based on the Y direction speed. I did it so it could generate forests and that lot, but it seems similar to what you're after so just have a look and figure out what I've done if you think it could be useful
http://peterhuntvfx.co.uk/gallery/script/instance/code

Look at the part after it says '#duplicate object to work on'

Only downside is the code is horrendously slow

[joojaa]

I thought there must be another way to do this either with procedural textures generated from the slopes of the terrain or by using Mel. >> It would be a lot quicker for look development to just tweak a few values rather than repainting the

Procedurals can be baed to textures/vertex attributes. Does the same thing.

slopes of the terrain or by using Mel.

Doing things in mel do not change the toolset. So if you can do it manually you can record the manual steps and viola you have mel. So the essence of being able to do a script is being able to do it manually without mel. So being able to do it manually is a prerequisite to mel.

So in this lightt didn't say anything about not doing it in mel i just pointed out that the steps are superflous. You donbt need to cull based on anything the toolset is allready there. Use it trough mel or not.

So i was talking of programming in mel. The setps you propose are extra steps as far as mayas concerned. But thenagain you can do this with expressions so no need for mel, python or api.

Only downside is the code is horrendously slow

oh dear oh dear o dear.

You huys should actullys top thinking of code and start thinking of nodes. Start by reading the node reference.

PS: anyway its far more trivial with paint objects (no you odnt need to paint you can floodbased on the texture), if for some reasin you dont really want to use instances (tough even that is a option.)