I created a mesh that has only vertices and converted it to a particle system representing the stars of the Hipparcos catalog.
I used image textures to control the colors and brightnesses of the stars, with each pixel of the textures encoding the color of each star by vertex index. I accessed these indices using a Particle Info node in the material for the dupli object (a simple sphere). This seems to have worked.
I want also to control the sizes of the individual stars, but for that I can't use nodes (or at least it doesn't look like it). All the posts I came across suggest that I should either weight-paint the mesh or generate an image texture and assign it to the particle system. I did the latter, partly because I don't know if I can weight-paint a mesh that has no faces or edges.
But it seems that I need to mind the mapping between the texture and the mesh. I suspect this is the reason I haven't succeeded at controlling particle size with image textures. I don't know how to go about doing the mapping, because it's just vertices, so I'm now considering weight-painting as an option.
So my question is... can I weight-paint a mesh that has only vertices and use those weights to control the sizes of 119,617 dupli objects in my particle system?
I know the challenge is the same—it's just vertices and how do I assign each a weight or a spot in an image texture to control particle size... I guess I'm just putting one foot in the weight-painting option in case it turns out to be doable.
Many thanks in advance for helping if you can!