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Suggestion required : How to inversely link yposition of layer A to xposition of layer B
Hi guys,
I am a newbie when it comes to after effects expressions, I have a very basic high school level coding background in c++ and flashscripts, so though I do understand most of the concepts I dont understand all of them so if you find my questions a little silly or naive please bear with me.Problem :
I want to link the Yposition of a layer (A) to the Xposition of another layer (B) in a reversed way.
For example, if the Xposition of layer B increases positively from 0 to 10, I want that value to affect the Yposition of layer A & change it from 0 to -10I have created variables namely xyz and made the 2 layer’s positions directly proportional and equal to each other but I dont know what to do next.
PS : if I’m not clear in what I am asking here; let me rephrase : This is for inversely linking X position of a layer to the Y position the positions of another layers in AFTER EFFECTS CS 5.5 with the help of expressions.
x = thisComp.layer("Medium Gray-Red Solid 1").transform.position[0];
y = thisComp.layer("Medium Gray-Red Solid 1").transform.position[1];
z = thisComp.layer("Medium Gray-Red Solid 1").transform.position[2];
[x, y, z] -
7 Replies
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There are a couple of different ways to interpret what you’re asking for, but in both cases, you’ll need a reference point if you want to calculate how much Layer A has moved.
This method uses the center of the comp as the reference:
x = thisComp.layer(“Layer A”).transform.position[0];
value – [0, x – thisComp.width/2]This method calculates how much Layer A has moved since time=0 and requires you animate (via keyframes or expression) Layer A’s movement before you’ll see any effect on Layer B;
x = thisComp.layer(“Layer A”).transform.position[0];
x0 = thisComp.layer(“Layer A”).transform.position.valueAtTime(0)[0];
value – [0,x-x0]Hopefully one of these will get you headed in the right direction.
Dan
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Thank you Dan,
x = thisComp.layer("Layer A").transform.position[0];
value - [0, x - thisComp.width/2]I understand that you are first assigning the X pos value to a variable x, and then using that x variable in the line 2 in place of Y pos. But I dont understand how the line 2 works to be honest.
Could you please explain this code a little further, on how it is working ?
For my initial question this works exactly the way I wanted it,
but in another instance I would also want to be able to link the X position of a layer A inversely with another layer B’s X position.How can I achieve that ?
EDIT : Disregard the 2nd part of my post.
x = thisComp.layer("Layer B").transform.position[0];
value - [x- thisComp.width/2, 1]I used ^ this code to achieve the same result. But please do explain how the line 2 is actually working.
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I’m guessing what you really want for the 2nd line of your version is:
value – [x- thisComp.width/2, 0]
value is an array that represents the current value of the position property (x is the first component of the array, y is the second–like this [x,y]). So the second line is just Array math that takes whatever the position value is currently, and subtracts how far (in the x direction) Layer B is from the middle of the comp, and subtracts 0 from the current y value (leaving it unchanged).
Does that help?
Dan
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Yes it does help but it raises other questions, very noobish questions.
So whenever under a property ‘value’ is written it means it’s pulling the value of that property ? Example if I created an expression in scale and wrote value – 80 it’d pull the current value of scale and deduct 80 from it?
When I write Value – 80 it only subtracts 80 from x and writing value -80,1 gives an error of dimension.
I now understand how this ‘Value’ function works (it pulls the value of the property under which it’s called) but dont understand yet how to use it.
ALSO
I thought [xyz] are the same as [012]
And thought writing [x variable, 1, 2] would mean writing [x variable, y z]
x = thisComp.layer("Nose Front").transform.position[0];
value - [x - thisComp.width/2, 0]Now that you mentioned it, when I code it in my comp putting 0 1 or 2 doesnt really change the way the 2 layers behave in any way.
I have positioned the layer that is being moved above the layer that is being affected. (To create a modified parallax effect)
The only difference putting 0 or 1 or 2 makes is the affected layer slightly changes it’s y (vertical) position.
Really appreciate your responses.
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>So whenever under a property ‘value’ is written it means it’s pulling the value of that property ?
Yes–the pre-expression value of the property.
The correct way to subtract 80 from the scale value would be:
value – [80,80]
unless you only wanted to affect the x value, in which case it would be:
value – [80,0] (note that value – 80 works for this, but I wouldn’t consider it good form)
You could also do it this way:
[value[0]-80,value[1]]
It’s all about JavaScript array notation.
>And thought writing [x variable, 1, 2] would mean writing [x variable, y z]
No. This would work:
x_variable = (something)
[x_variable,value[1],value[2]]Instead of “value” you can use the property name:
[scale[0],scale[1],scale[2]]
but using “value” makes the expression more generic, and more portable to other properties.
Dan
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Thanks a lot Dan.
Though I understood most of what you have explained to me here, could you do me 1 final favor by telling me what to google or where to look to learn and find out the significance of the [1] [2] or [0] ?? So I know what is their exact function in a script and when to properly use them ? Should I google JavaScript array notation ??
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This old article from my site might be of some help:
https://www.motionscript.com/mastering-expressions/language-beginning-3.html
Dan
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