I'm in charge of making the crowd butterflies and the tree.
Dorothy made one tree before she left for exchange, but we find that the result is not very well, so I remade one.
The technique for making the crowd animation is quiet new for me. Eddie helped a lot by giving me the tutorials and the expression codes.
But even though, I have watched lots of tutorials and have the pdf Eddie gave me, I still encounter some problems. Oh, it's not some, it's a LOT...
What I used to made the final butterfly crowd is not based on one tutorial, but based on numbers of different tutorials. For each one of them, it works very well, but when I tried to combine those together, problems come out.
Finally, I came up with these conclusions:
1. Particle grid can have the random rotation, random size, random position, random start-time, but it's difficult to move them smoothly.
2. Particle emitted from object cannot bare the creation expression for random size and scale.
3. Flow particle is a good way to animate the particle moving curve, but not work well in random size.