[kdenlive] Transitions Wipe Dissolve Slide: Reverse Parameter

[Harald Albrecht]

Dear Kdenlivers,

in the on-going discussion of Kdenlive transitions I also came across 
the "dirty three" of wipe, dissolve, and slide. To me, these are the 
perfect examples of crossfade transitions.

What I still find difficult to get right is the "reverse" checkbox in 
the transition properties for the "dirty three". Playing around with it 
I actually see that the reverse parameter is controlling whether the 
transition starts with the upper track clip or lower track clip. So 
instead of the "reverse" checkbox which is probably one of the bad UI 
things in Kdenlive, what about having a selection box that has exactly 
these two items: "from upper to lower clip" and "from lower to upper clip"?

In the future, Kdenlive might even guess the correct setting for the 
reverse parameter by looking at how the transition is placed with 
respect to the two clips involved. Of course, there are still situations 
where Kdenlive can't correctly guess, but this wouldn't be an issue as 
this would be only an initial guess and users can change it later at any 
time. So, if the upper clip starts earlier than the lower clip, set 
reverse to "from upper to lower clip". If the lower clip starts earlier 
than the upper clip, set reverse instead to "from lower to upper clip".

In the long run, adding in-track crossfade transitions could hide this 
ugly reverse parameter from users completely. An in-track crossfade 
avoids the ambiguities possible with two-track crossfades. Please note 
that I don't think of removing two-track crossfades, though!

Comments on this idea? Suggestions?

Best regards,
Harald