[PD] Crossfade between 4 films moving a slider

[Nuno Godinho]

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