Selecting start points in chop and create a line

[renklint]

Hi,

 

this is the input from a midi-in chop. 

 

 

I would like to get only the starting points, where the midi-file changes notes.

 

 

And then create a line between these points, I guess that can be done with the add sop.

 

 

But how to select only the start points. A trigger chop would give me the right time, but not the value at that position.

[Atom]

Checkout the function chops(opinputpath(".",0")). This should get you your starting value from there chop channel.

 

For instance, use a Shift node (in CHOPS context) and then place the expression -chops(opinputpath(".",0")) in the Start field. This will create a shifted chop whose start will always be at 0. Then you can use a Delete by pattern 0 (non-selected) to fetch that value.

 

chops gets you chop start.

chope gets you chop end.

Edited March 19, 2015 by Atom

[renklint]

Thank you Atom.
 
I'm doing something wrong, because everything but the first point gets deleted.

 

 

 

test_opinputpath.hipnc

 

Point the midi-in chop to this file: https://www.dropbox.com/s/vftlfa0vdwnx4v4/skala.mid?dl=0

 

 

 

[sadhu]

try this 

if (chopi("../math1/ty",$I)>chopi("../math1/ty",$I-1),$V,0)

in expression/expression1 chop.

[renklint]

Thank you sadhu!

 

That definitely catches some of the points:

 

I can't say that I understand what it does though.

Now I'm readign that the chopi expression function evaluates a channel at a given sample point.

Ok, so the expression compares the points and if the y-value is higher than the one before it is kept, otherwise it is set to 0.

Changing the > to a < produces the remaining points.

 

How does one rewrite the expression so that it matches points bigger than or smaller than the 

point before?

 

Then I can probably just use a delete and delete all points of value 0.

[renklint]

Found it.

 

if (chopi("../math1/ty",$I)!=chopi("../math1/ty",$I-1),$V,0)

 

Thanks again.

[sadhu]

ohh.. I didn't realize that its not selecting all the desired points. Good ! You got it working.

[renklint]

Just have to figure out how to include the very first point...

[sadhu]

if($I==0,$V,if (chopi("../math1/ty",$I)!=chopi("../math1/ty",$I-1),$V,0))

[renklint]

Thank you!

So there's no else if in Houdini, good to know.