Black is less dense, white is dense. Or vice versa it doesn’t matter. Particle just need to follow a guide from cycles node editor
And you are 100% sure that you want to use the node editor and color ramps to adjust vegetation distribution? Whats the point of the addon in that case?
The best way of doing this would be to have your addon calculate all these parameters per vertex in a separate thread and just give the artist sliders to play with the settings. Visually you would just update the contrast of vertex colors and copy values to vertex group weight.
Something that works like vue would be great & they can use the node editor for the distribution off the vegetation etc… 
The best way of doing this would be to have your addon calculate all these parameters per vertex in a separate thread and just give the artist sliders to play with the settings. Visually you would just update the contrast of vertex colors and copy values to vertex group weight.
This is a ton of work. it need sliders for Occlusion/slope/elevation/pointiness…ect and all of this can be done with a material set up. it’s already inside of blender.
that’s why i’m asking this question.
If terrain can be fully unwrapped from top view, you can just add UV slot, then apply UV project modifier and do f12 render from top view. Thus avoid edit mode and setting image for default baking
You got really god answers… and still this can’t be done the way you want it to work, directly with blender native tools, no matter how much you want it. For non destructive workflow you would want to have it done in python, and recreate that setup from cycles. If you don’t want to expose parameters for artist via addon you could maybe read positions of the colorRamp sliders and mix factor (if its even possible i know you can set the values through api), which looks like nightmare to me… what if you want to change the setup and add more nodes to affect the mask…
Sorry i don’t really understood what you said
For now i only had one answer to my question and it’s not non destructive. It’s the automatic UV unwrapping, automatic baking and auto set up to texture and vertex group.
i doubt that it’s a good solution for an addon but i will try this at some point and if i use it because it’s actually working i will for sure give @Serge_L his 20$
Well IMO, a good answer is not necessarily one that solves the problem, i meant in general there were some good points especially from @ambi “Plus Cycles is a rendering engine, not a data transformation tool”
For an addon solution you would pretty much want what @Serge_L did with AN
Sorry but i understood your response as “Why don’t You don’t give the reward you had perfect response” Is this what you meant ?
No, ofc not. What i meant with that is - you can’t transfer shading data to particles the way you imagined it, in a direct non destructive way, without baking or doing something else. I got impression that you don’t want to get over that part. Sorry if I caused any confusion
even with python ?
no indeed i really don’t. it seems so simple to do its only but black and white colors 
how could this be so hard to transfer
Because, node editor is not designed for that -> "Cycles is a rendering engine, not a data transformation tool”. Node editor has only one output and that is a shader program.
I can see how what you want can be useful but unfortunetlly its not currently possible.
As for python? Yes its doable and its not that hard, but it has nothing to do with cycles.
You can compute all the masks and bake them to vertex colors using python and it should work fast. Then you can display that in cycles and there’s your non destructive workflow.
is it even possible to do a bmesh analysis of a terrain if he only exist because of the displacement modifier ?
Yes, you can check out my work on Illuminato that does that on any mesh.
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