[PD] Crossfade between 4 films moving a slider

Hi there,

Using a MIDI slider (0-127) I have to crossfade between 4 films separated by regions. When the slider is between 0-30 film A is displayed, when it moves from 30 to 31 it quickly crossfades to film B, then at 60/61 crossfades to film C and finally at 90/91 crossfades to film D.

I was building this making use of three cascading pix_mix. But then I figured if it wouldn't be simpler to, instead of cascading, play with pix_alpha on each picture independently and thus creating my own crossfade. This way I would get more control over each film and build something more modular. The idea is: when the fader moves from 30 to 31 I use pix_alpha to make film A disappear at the same time making film B appear. Do you think this is a good approach?

How is crossfade built anyway? How is pix_mix implemented? By using alpha channel, right?

Any better ideas?

Thanks in advance, Nuno