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Situation

I am working on a visualiser that sprays fire at the start of the drop

  1. In my Scene there is a 2D animated background, multiple thousand frames long
  2. I have two fire fountains which spray two times for about 80 frames within the former animation time
  3. This fire fountains takes about 2 hours to render each time these frames are hit, and the fountains are always the same
  4. The camera constantly shakes

The scene from the side (ignore the overlap of the fire with the other stuff, it doesn't matter) Side view From the camera (beware that it shakes, so it won't stay exactly the same) Cam view Rendered Rendered

Goal

I want to pre-render the fire and then somehow insert it to drastically reduce render time, and I can't simply layer it because the fire is 3D and the camera moves.
I have no idea how this can be achieved and would appreciate any suggestions :)

Progress

I now have this node setup, but I don't know how to get rid of the black background. Everything I found was for cycles. enter image description here

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You can pre-render only the particle effects, then add a frame of the animation using Add Images as Planes (enable the add-on).

Then parent the image plane to the backdrop and change the source from a still image to a video sequence.

You can separate them out into different layers and then composite them together in the Compositor.

If you render with alpha, use the Alpha Over node. If you render against a black background use a MixRGB node set to "add".

The Compositor will also allow you to add things like glow effects if you want by using a Blur node.

Probably worth testing your workflow on a small number of frames first to make sure everything's working before rendering the whole thing.

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  • $\begingroup$ I have never used nodes yet. Could you provide me with a screenshot and explain the purpose of "backdrop"? $\endgroup$ – Xerus Jun 30 '17 at 15:04
  • $\begingroup$ By "backdrop" I just meant your 2D animated background, as you call it. Whatever is to be separate from the fire. $\endgroup$ – Mentalist Jun 30 '17 at 15:08
  • $\begingroup$ OK, I made an edit, please help me to complete what I have. I rendered a video with black background and can't get that to be transparent. $\endgroup$ – Xerus Jun 30 '17 at 16:08
  • $\begingroup$ btw would it make sense to turn off anti-aliasing when rendering the fire itself? $\endgroup$ – Xerus Jun 30 '17 at 16:40
  • $\begingroup$ Don't worry about the anti-aliasing; you can leave it on for everything you're doing. There is a setting for background transparency in your Render context tab. The location and naming of the setting are different in Cycles and Blender Render, but you can look it up easily online. I don't have a computer in front of me now to check your .blend (only iPhone), but hopefully this helps. $\endgroup$ – Mentalist Jul 1 '17 at 23:43

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