Linking Null position to 3 other to Control Position with Checkbox Constraints

[Dan Ebberts]

In what way to the other nulls “influence” Null 1’s position? What does that mean, exactly?

[Dan Ebberts]

If you want Null 1 to move based on the relative movement of the other nulls, the other nulls need reference points. One way to do it is to keyframe their movement and Null 1 can take on movement of the other nulls that has occurred since time = 0. That would look something like this:

n2 = thisComp.layer("Null 2");
n3 = thisComp.layer("Null 3");
n4 = thisComp.layer("Null 4");
includeN2 = effect("Checkbox Control")("Checkbox") == 1;
d2 = n2.position - n2.position.valueAtTime(0);
d3 = n3.position - n3.position.valueAtTime(0);
d4 = n4.position - n4.position.valueAtTime(0);
val = value + d3 + d4;
if (includeN2) val += d2;
val

Null 2’s movement only gets included if the checkbox is on. If you want to animate the checkbox, that’s a much more complicated proposition…

[Sandro Maia]

Hi Dan,

What I mean is that all three nulls should be able to move Null1 as if it were a regular null. However, I want to add a checkbox that allows me to toggle whether Null2 can control Null1’s position. The checkbox doesn’t need to be keyframed, although that would be a plus if it could. But this should all work with no keyframes at all and if I want to keyframe the position of any given null I would want that possibility. Would this be possible?

Let me know if that makes sense!

[Dan Ebberts]

>as if it were a regular null.

I have to confess, that I have no idea what that means. Are you talking about parenting?

[Sandro Maia]

Sorry Dan, English is not my first language, so it might be difficult to translate ideas, if it helps this is what i tried:

It mostly works, if i uncheck the checkbox the layer stops following Null 1, the problem is that when i check the box for it to follow again, the layer has an offset and its moving more than it should.

var checkbox = effect("Checkbox Control")("Checkbox");
var null1 = thisComp.layer("Null 1").transform.position;
var null2 = thisComp.layer("Null 2").transform.position;
var null3 = thisComp.layer("Null 3").transform.position;

// Always follows Null 2 and Null 3 wether checkbox is on/off

if (checkbox == 1) {
    // If checkbox is checked, follow Null 1 and Null 2 and Null 3
    null3 + (null1 - null2)
} else {
    // If checkbox is unchecked, follow Null 2 and Null 3
    null3 + (null2 - null1)
}

[Sandro Maia]

Also here’s the project file if you want to take a look

Null-test.aep 420 KB After Effects Project Files - Click to view

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[Dan Ebberts]

Ah, OK. I don’t think you’ll ever be able to set it up so that the position doesn’t change instantly when you toggle the checkbox to bring the influence of Null 2 in or out. There’s no way for the expression to know the history of the checkbox (unless it’s keyframed or controlled by an expression).

[Sandro Maia]

Thats unfortunate. Okay thank you. Do you think its possible to fix that offset of the Null 1 when the checkbox is on? I can’t for the life of me figure it out…

[Dan Ebberts]

I don’t understand your formula. Why does having the checkbox on flip the effect of null1 and null2? It seems like it should just remove the effect of null2.

[Sandro Maia]

I see your point, but if i remove null2 the layer jumps position to another place in the comp.