I use Blender 2.68 and also 2.69 both have a problem using a vertex group to influence particle sizes. The blendfile is attached.
I created an icosphere, then a cylinder. I sized down the cylinder and applied rotation and size. It should act as particle. The origin of the cylinder is the center of the bottom circle.
Then I weight painted the upper part of the icosphere with value 1 the rest keeps at zero, vertex group is standard called ‘Group’.
I added a particlesystem type emitter to the icosphere, under ‘Render’ I selected ‘Object’ and entered my cylinder as particle.
Under ‘vertex groups’ I choosed ‘Length’ and picked ‘Group’ as vertex group which should influence the size of the particles.
Immediately all particles rotate to the right as shown in the first picture.
If I hit tab to enter edit mode and tab again to enter object mode again, the particles switch to their original position but the vertex group does not effect the size. All particles still have same size.
If I hit ‘Negativ’ (on the right side of vertex group setting for ‘Length’) then all particles rotate to the right again.
If I hit tab and tab again, they rotate back but no influence on the size / length.
Another weird thing:
If I switch the ‘Negativ’ box to enabled or dispabled and immediately after that I open the ‘Display’ option of the particlesystem settings and move the slider from 100% down to 0% and back to 100% sometimes a few particles keep out of the sphere. It seems that there are some problems inside particle system?
Same happens in Blender 2.69.
What I am missing?
ParticleSize.blend (717 KB)