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Thread: particles take longer as scene ends?

  1. #1

    particles take longer as scene ends?

    I have a scene with smoke particles, and despite that there's less and less smoke being rendered right now, the final frames are taking longer and longer!

    I thought 1'30" was going to be the longest frame, but over the weekend, it got to 2'30" and now I see one that rendered this morning at just over 3 hours!

    the amount of smoke visible to the eye right now is prbly less than 1/10th that of the most "smoke-filled" frame.

    I had a thought last night, that maybe LW is carrying all the calculations FOR that smoke, beginning with the very first frame containing smoke, and that all successive smoke is based on those calcs...

    So, that (my theory goes) after 100 frames' worth of smoke, you've got 100 frames' worth of previous smoke calculation, not just the one rendered in THAT frame.

    is that how it works, and is that why my less-smoke, later frames are taking longer than my more-smoke, earlier frames?

    and, what's the solution? I hope my very last frames don't ramp up to some unspeakable per-frame render times...


    thank you!


    J
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    Discuss sustainability at www.ThinkPlan.org

  2. #2
    Super Member SplineGod's Avatar
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    If youre increasing the HV size as time goes on and the HVs are not dying off very quickly the time for calculations will take longer.
    Render times for HVs are going to take much longer when the HVs are larger.

  3. #3
    OK...IIRC, my particle size is constant, but I did give them a pretty long life span...


    yet, I don't see lots of lingering smoke..in the frames rendering now, it's just a whisp compared to mid-way thru the sequence, when the smoke more or less filled the room.

    J
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    Discuss sustainability at www.ThinkPlan.org

  4. #4
    Super Member
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    I had a similar problem a few weeks ago. I ended up using smaller HVs and playing with the density/opacity and quantity of particles. Also started the particle generation sooner and ended it later to take advantage of the optimal look during the frame range I wanted.

  5. #5
    Quote Originally Posted by medicalart View Post
    I had a similar problem a few weeks ago. I ended up using smaller HVs and playing with the density/opacity and quantity of particles. Also started the particle generation sooner and ended it later to take advantage of the optimal look during the frame range I wanted.
    those are good ideas...... I'm going to take one step related to getting the best particles to coincide with the desired frame range: for various angles, I will render *just* a select range of frames...

    I'm assuming the closer the cam is to the particle source, the higher the times, so I may be in for some glacial frame production rates here..

    J
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    Discuss sustainability at www.ThinkPlan.org

  6. #6
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    Camera distance didn't seem to make much difference, but multiple overlapping hypervoxels slowed things down. There's a little box to check to "view particles" which should give you an idea of how much they overlap. Because I was using very delicate sprites, I had to use a lot of them and make them larger. When I upped the density I could use fewer and rendering times improved.

  7. #7
    Quote Originally Posted by medicalart View Post
    Camera distance didn't seem to make much difference, but multiple overlapping hypervoxels slowed things down. There's a little box to check to "view particles" which should give you an idea of how much they overlap. Because I was using very delicate sprites, I had to use a lot of them and make them larger. When I upped the density I could use fewer and rendering times improved.
    excellent information..thank you for passing it along. I'll play with that, too!

    J
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    Discuss sustainability at www.ThinkPlan.org

  8. #8
    Do you happen to be using the thickness parameter? If that gets too low, your render times can skyrocket, too.
    Are you able to provide the scene? It would be understandable if you didn't want to give it out
    Also, if ray trace shadows is on, try disabling it and seeing if your render time improves.

  9. #9
    thickness? not sure if I did or not...

    you mean the opacity of the particles?

    this render has been going for about 2 weeks and will prbly last another week yet..been awhile since I actually worked with that scene!

    ;-)


    J
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    Discuss sustainability at www.ThinkPlan.org

  10. #10
    Hmmm, my mistake! I thought you were using Volume voxels, but now I think they might be Sprites. Sprites don't have a Thickness parameter

  11. #11
    right..you are right I am using sprites. I don't have their size or opacity change over time.

    the only thing that changes is their color, over their lifespan, and they do have a fairly long lifespan...

    I might have played with that more, but the test renders looked so dang good I really didn't want to tinker too much.


    J
    _______________________________________
    Discuss sustainability at www.ThinkPlan.org

  12. #12
    I find it odd that sprites would take so long to render, unless you have an old comp. What settings do you have for antialiasing and motion blur?

  13. #13
    motion blur: none

    anti-aliasing: enhanced low

    I'm using a couple of 1.42Ghz PPC Mac Minis here, each with 1-gig sticks.

    yes...they're practically horse 'n' buggy compared to what others are using these days...

    J
    _______________________________________
    Discuss sustainability at www.ThinkPlan.org

  14. #14
    Hmmmm... I think I'm out of ideas besides the disable-ray-trace-shadows one From my experience, it can make your render times 10x longer and make little difference to the rendered image.

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