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Parenting nulls to trigonometry-controlled objects
I want to build a digram with arrows between some boxes, where the arrows are connected to the edges of the boxes. So if I move the boxes around, the arrows with change length and angle.
I’ve read tutorials about how to connect lines to other objects dynamically, using the Beam effect, but I want arrows!
Using this post – https://forums.creativecow.net/thread/227/6984 I was able to build an arrow that is controlled by two nulls (at the start and end).
But when I try to parent one of the start or end nulls to another null or object, the parent object doesn’t move the child object.. What am I missing?
video example here.
Below are some snippets of my dodgy code:
arrowlength controlled by<code>CellTower = thisComp.layer("startpoint").transform.position;
Target = thisComp.layer("endpoint").transform.position;
sizefactor = 100/(effect("ArrowSize")("Slider"));
BeamLength = (length(CellTower, Target)*sizefactor)-150;
[BeamLength]
</code>rotation of the arrow controlled by
<code>CellTower=thisComp.layer("startpoint").transform.position;
Target=thisComp.layer("endpoint").transform.position;// Find the length of side a
SideA = sub(CellTower, Target)[1];// Find the length of side b
SideB = sub(CellTower, Target)[0];//Find the Angle between them
-1*(270-(radiansToDegrees(Math.atan2(SideA, SideB))+180));</code> -
5 Replies
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Hi,
Thanks for the suggestion… I thought about using puppet pins, but I really wanted to keep the geometry of the arrows just right – they seem to look fine though, unless they’re really short.Having said that, I still can’t get the two nulls to parent to other objects without everything breaking.
I really need to be able to dynamically move some boxes attached to the arrows.Here are my steps:
* Load your .aep project
* Make a shape – a rounded rect box
* Change it’s anchor point (using, but could just as easily be a manual adjustment)
* Duplicate the shape
* Change shape two’s anchor point
* Reposition the arrow nulls into the right places
* Parent Null 1 (the base of the arrow) to Shape 1See video here:
https://www.youtube.com/watch?v=bed23MzoUUUImmediately the arrow shape jumps off to the side. Why?
Many thanks again for the suggestion.
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I’ve just realised, if I re-write the expression on the puppet pin to point to the shape layer it solves my problem!
Many thanks-
I’m still stumped as to why I can’t parent a null to another null successfully though…
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Also, by adding a Layer Selector to the expression, I can choose which object the arrow starts and ends from:
Based on the excellent tutorial by Felt Tips here: https://vimeo.com/104381026
try {
L = effect("Arrow Base")("Layer");
} catch(e) { // catch an error in case layer is set to None. Stops expression crashing
L = false;
}
if(L)
fromWorld(L.position);
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Parenting messes up the coordinate transformation, and it can get complex. I often end up using “value +” (or a specific value) to change the position. You can get it to work with expressions as well, but I don’t personally find figuring out the right combination of fromComp/toComp/fromWorld/toWorld very easy with a more complex setup, so I just take the easier way.
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