When I finished the plants tutorial, I was wondering what I could animate in this scene. But when I thought about 7 minutes render time per frame, I realized that I would likely not finish a 3 seconds animation.
A relative of mine posted a comment on my light streaks and he pointed out that the fog creating the light streaks is very homogenous. So I went into the Compositor and fixed it by mixing in a cloud texture on the fog. Meanwhile it’s pretty deprecated to explain, because Andrew uses the same approach in the lakes tutorial as well, but for the sake of completeness, here’s the node setup for it:
With this setting made, I got the following result (it has antialias effects because I didn’t know one needs to rerender; Andrew explained it now in the lakes tutorial):
While doing this, an idea came into my mind. If it would be possible to animate the texture, I could render an animation of it and the fog looked like in motion. The only thing I didn’t want to do is rerendering the scene for every image. That’s why I saved intermediate results from the Compositor using File Output nodes. I can’t go too much into detail here, but just save the direct output of the streaks and then the scene including background into separate files (I used EXR files).
Next, open up a new blender file, delete the cube. In the render settings uncheck all passes and all includes (like sky, solid, halo) and simply setup Compositor nodes like this:
One odd thing I found is that Blender does not support vector input nodes, only value input nodes. While a value node holds only one value, a vector holds X, Y and Z values. To fake this, I am using an RGB node. Somehow the RGB values map to XYZ with the limitation that the range is from 0.0 through 1.0 only. This doesn’t matter for this scene as we need very low values anyway.
Now, extend your scene to have 1000 frames and go to frame 0. Make the color of the RGB node which is connected to Offset pure white (1,1,1), then hit the I key to insert a keyframe on it. Do the same for the RGB node which is connected to the scale input. Move over to frame 1000 and set the offset color to pink (1,0,1) and the scale color to bright pink (1, 0.7, 1). Make sure to set keyframes on both of them again.
Jump over to the video editor and make sure that the paths are linear. Press the Home button to view all and make things linear using Shift+E. Now render a single frame (F12) and it should not take longer than 3 seconds.
Ok, so if this is set up, render the animation into single pictures (full HD PNG will need 2 GB hard disk) and later combine it into a video as described by Blenderguru before. With this, I’m getting a full HD video in less than one hour which looks similar to this (note that this early version has non-linear keyframes which looks strange):
Download fog animation in full HD (26 MB) (please right click and save. Bandwidth is probably too low for streaming directly from my server)
I’m sorry I could not provide a video tutorial about it, but I’m going into holidays and wanted to share this with you before I leave. Please post any suggestions or improvements in the comments.