The situation:
I have a particle system set up and applied a halo material to it. The particles have a lifespan of 300 frames.
Aim:
Animating the alpha of the particles, but based on how long they are already alive. More specific: I want the particles to have an alpha of 0.5 from the start till 200 frames of their lives and then gradually lower it to 0.0
Problem:
When I IPO-curve the alpha value of the material, all particles have an alpha of 0.0 at frame 300. Also the particles that were just born. What I want is that a particle that is born at frame 250 keeps an alpha of 0.5 till frame 450 and then lower to 0.0 at frame 550.
Of course I googled a bit and did a search on this forum, but it didn’t turn up a solution (pity you can’t search for ‘ipo’ here at blenderartists). So any suggestions are highly appreciated.
You need to animate your particles’ halo material over 100 frames. Blender applies the 100 frame animation over the lifetime of the particles, so if a particle lives only 10 frames the 100 frame material animation is compressed into 10 frames.
To get the effect you want, set alpha to 0.5 on frame 1, press I to set an alpha keyframe (make sure the mouse cursor is over the material settings), goto frame 66, press I and add another keyframe, then go to frame 100, change alpha to 0 and press I to add another alpha keyframe.
Short summary for future reference:
You have to set the keys for the IPO curve from within the materials window (with the I-key). What I did wrong was that I created the IPO curve manually inside the IPO curve editor with CTRL+LMB. Of course it’s also important to define the curve within 1 - 100 frames, not outside it.