I want to populate trees along a road with Particles using weight painting to control the density. My problem is that the particle system needs to know the final particles count - logically, I proceed from start to finish so with every newly painted areas, the tree density will more and more decrease as this number spreads to bigger area. This means I have to adjust and estimate the count every while, which is frustrating. So is there any option how to tell the particle system to produce maximum (based on a weight paint) of 5 instances on area of i.e. 10x10 meters so the number of instances / particles will grow progressively as I paint? enter image description here enter image description here enter image description here

  • $\begingroup$ If you use a Hair Particle System you can influence the Length instead of Density $\endgroup$
    – HenrikD
    Commented Jan 21, 2019 at 8:23
  • $\begingroup$ @HenrikD I tested this now and it doesn't look like this changes particles count. $\endgroup$ Commented Jan 21, 2019 at 11:35
  • $\begingroup$ No but you dont need to adjust it. You just need to have all the particles you dont want to be invisible (scaled down to 0) $\endgroup$
    – HenrikD
    Commented Jan 21, 2019 at 11:37
  • $\begingroup$ @HenrikD But this way milions of trees / particles will be hidden and only those in weight painted areas will be shown...? $\endgroup$ Commented Jan 21, 2019 at 11:42
  • $\begingroup$ yes! I dont know how much it affects the performance, you have to test it. $\endgroup$
    – HenrikD
    Commented Jan 21, 2019 at 11:43

1 Answer 1


As I haven't found any solution so far and this fixed-count workflow limits my daily work a lot, I have refreshed my "so-so programming skills" and I ended up with creating a Blender (2.79) addon which does this job for me.

With the addon, you set the Density parameter and the Emmission Number is adjusted accordingly:

enter image description here

I have placed the addon to Github and would be very happy is someone can test it and report any bugs. https://github.com/jendabek/blender-particles-density

  • $\begingroup$ Ah, a great addon! Can surely use it if not recommend it to my friends! It has a similar function as the density in Graswald $\endgroup$ Commented Apr 26, 2019 at 18:10
  • $\begingroup$ Thanks, first I would like anyone to test it properly as I am not very skilled Python programmer and even it works for me flawlessly, there can be some bugs when i.e. using some different workflows... $\endgroup$ Commented Apr 26, 2019 at 18:23
  • $\begingroup$ OK, can I rewrite it to work with 2.8 or do you want to do that yourself? Asking since I want to get better at coding too $\endgroup$ Commented Apr 26, 2019 at 20:32
  • $\begingroup$ @DrachenSeele Of course, just create a branch or something like that :) $\endgroup$ Commented Apr 27, 2019 at 8:55

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