Using sourceRectAtTime expression to recreate comments section

[In The Corn Productions]

Hello!

I am currently working on a project where I have to recreate the comments section of a youtube live video. I am trying to create a situation where I can type in each comment individually and have the layers adjust to the "posting" of a new comment as though it would on a platform like youtube / tiktok /etc.

I have never used sourceRectAtTime, but it was recommended to me for this. I am also open to any plugins that might solve this conundrum for me as well.

I have attached a reference sample of what I'm looking to do (which was created manually).

Any help would be much appreciated!

[Mylenium]

Completely unnecessary. A simple text layer with a text animator that has its mode set to Line would do everything you need. This isn't anything like those messaging apps with text bubbles.

Mylenium 

[In The Corn Productions]

Ah! after looking into sourceRectAtTime more I was hoping the answer would be a bit simpler. However, I am still relatively new to AE. Would you mind explaining in further detail?

[Rick Gerard · Accepted solution]

You can use sourceRectAtTime() to calculate the height of a text layer. Add inPoint to the end and some padding, and you can easily make a layer jump up when another layer starts. All you need is an expression on the text layer's position property. If you throw in an if statement and interpolate the movement, and put the expression on all but the bottom layer, you can get something like this:

Here's the expression:

ref = thisComp.layer(index + 1);
refH = ref.sourceRectAtTime().height;
refP = ref.position;
y = refP[1] - refH - 20;// 20 is the padding between layers
x = refP[0];
m = .3; // move time in seconds
t = time - ref.inPoint + m;
if (time <= ref.inPoint - m){
	refP;
}
else{
	y = ease(t, 0, m, refP[1], y);
	[x, y];
}

[In The Corn Productions]

This might just be exactly what I need! thank you so much 🙂

[In The Corn Productions]

Looks like this is working great so far, but if I add a comment that is a different size than the previous (ie. first comment is 2 lines of text and 2nd comment is 5 lines of text) then the spacing gets messed up. Is there a parameter I need to change to prevent that from happening?

[Rick Gerard]

You must add top and left to the expression to compensate for different layer sizes. I don't have time to rewrite the expression for you, but I do have time to tell you that this expression will return the current position of a text layer no matter what the paragraph justification or the baseline shift is:

ref = thisComp.layer(index - 1);
p = ref.position;
ls = ref.sourceRectAtTime(); // layer size
x = p[0] + ls.width/2 + ls.left;
y = p[1] + ls.height/2 + ls.top;

[x, y]

As long as the Anchor Point of both layers is at the default position, the expression will always position the layer below a text layer exactly at the center of the layer above. 

Combine that position plus half the width and the left edge and half the height and the top of a text layer, and you can setup the previous expression to calculate the total move and adjust the spacing based on layer size. Pay attention to how I combined the srAt.left and the srAt.top with the height and width of the layer, and you should be able to fix the problem with multiple lines of text.

[Mylenium]

https://helpx.adobe.com/after-effects/using/animating-text.html#animate_text_with_text_animators

Mylenium

[In The Corn Productions]

I mostly was unfamiliar with changing the mode to line, but I have used text animators before. I will do some reading - thank you!