path resolution / interpolation

hi all, back after some time…

probably not the best topic name, but the proper name would be the description itself.

here’s the situation: i have a 1-vertex particle emitter that follows a curved, wavy path. the emitter has all emission velocity settings at zero, thus leaves a halo trail behind (exactly the effect i want, and that works so far). time length was set to default 100 frames and everything looked perfect when rendered.

then i needed to change the length to 50 frames, and unfortunately the trail looked now as if it was made of a few linear segments. i raised the default resolution of the path, but that didn’t help either.
now it appears to me that blender only takes into consideration transformation values at full frames - which works perfectly for most purposes. but using the halo trail there is important information between frames, which is obviously dropped.

so the main question is if this is a limitation of blender or not. not sure if i should consider it a bug. just wanted to share the info while looking for a workaround (in postpro)



Interesting. What happens if you increase the Keys which I think is just another word for frames?


forgot to mention that: no effect.

w00t, my first dip into the blender code…

In answer to your question: yes, this is a limitation in blender.

The problem is in /blender/source/blender/blenkernel/intern/effect.c in build_particle_system, about 2/3 of the way through - it specifically does a linear interpolation between the two frames to find the position to create the next particle.

However, I’ve found a workaround:
Double the pathlength and the particle start and end times, halve the particle velocities and forces (if any) and add a 2:1 time ipo speedup on the particle system. Makes there be twice as many little linear segments in the particle path. Of course you could triple or quadruple the numbers to get even better results.

ah good to know. … i’ll have a look there. would it invole a major mathematical magic to fix that? i have little experience with the code and am particulary bad in maths :wink:

thanks for the hint anyways. right now i’ll stick with the static version (no animation).



i know this is off topic, but is there a tut somewhere for making trails like this? i would like to add a small trail to the ufo i’ve created in an animation.
sorry to break your topic.

well as i said in the first post (here just some more details, step by step):

  • create an emitter of 1 vertex (=make a plane and delete 3 vertices. place the last vertex at the obejct center if you want). give a meaningful name (easy to select afterwards in outliner by name)
  • go to F7 >> effects and activate particles. for a “motion trail” (one that describes exactly the motion of your vehicle) leave all settings that deal with the particle velocity at their default values - zero! what you’ll need to tweak is maybe the particle count.
  • move the emitter to your vehicle and parent it to it
  • move your vehicle around, make keyframes for your animation (if you didn’t already)
  • select the emitter and hit “Recalc All” in the particles tab. or simlply press TAB twice to enter and exit edit mode. this forces the particles to be recalculated, too.
  • the rest is tweaking material values for the emitter (F5). switch to halo (particles are rendered as halos automatically, but you also want control of all settings)
  • make material IPOs (for the halo material of the emitter) for halo size, transparency and such to make it fade out nicely before the particles disappear suddenly (defined by “Life” in particles tab)

have fun