how to link the x size parameter of a bezier path to the size of a text box and make it auto change as I change the text itself?

If you want a bezier path to auto change with text length, you need to use the 'track point' behaviour. The cross shapes are anchored to the sides of the text by using link behaviours. Then point 1 of the bezier is tracked to cross 1 and point 2 of the bezier is tracked to cross 2. The bezier is animated and it will always adjust to the position of the crosses, which are adjusting to the width of the text.

This will work in FCPX when published, but, there is a known bug in FCPX that prevents this working if the path is an airbrush or image brush with dynamics turned on.

Hi

The cross shapes are in your Motion 5 contents library - search for 'cross-hair minute'. ( or you can use any shape as a source).

Put your cross points into a new group, and in the group properties, check the 'fix resolution' box.

1: Link the cross shapes to the text bottom left and bottom right corners.

Cross 1:

Link X position the text 'left edge'

Link Y position to the text 'bottom'edge

Cross 2

Link X position to the text 'right edge'

Link Y position to the text 'left edge'

If done correctly, you will see the crosses adjusting to the length of text.

2: Draw your bezier path between the cross points.

3: Add track point behaviour - and use the left side cross as the source - you want 'attach to source' and you need to deselect point 2 in the menu - make sure you click the little 'reset parameter' arrow. - ...now you can run the 'analyse; for tis point.

4L Add the second track point behaviour - use the right side cross as the source, deselect point 1 in the options, ..follow the same steps.

There's plenty of information about using the track points behaviour here

https://support.apple.com/kb/PH16569?locale=en_US&viewlocale=en_US

Hope this helps.

The features you need in the Link behavior were added in Motion 5.3 when Align To was introduced. Is there any chance you can upgrade Motion to at least 5.3?

"I am using Motion 5.2"

sorry, missed that one, indeed 'Width' is one of the few true enhancements made in the past years to Motion....

Any reason not to update? (it's free …)

As you see in rowies helpful and elaborated reply, the 'old' method is by far more … complicated ;)

Plan C) publish the X-scale of the Bezier as a Rig… so, you do have a handy slider to manually adjust 'width' of Bezier to 'width' of text... not automatics, but at last an easy to use control (??) …

Like that?

By linking the Beziers X-scale with the Text Width:

Hi **1lder

I'm glad this helped.

When you do update, you will have all those additional parameter options for making relationships between text strings and objects.

Keep in mind, that there is a difference between linking 'width to width' and 'scale to width'

Liking scale to width can produce skewing and distortions in the shapes - this may or may not be a problem depending on what you want to happen.

A bezier path has no width parameter - so you can only link scale to text width.

However - as I learned from Karsten, ..in many situations, you do not have to use a bezier path or line tool to make a line. You can just adjust a rectangle to make a line - and then, you can make a 'width to width' link. You can make a line with a rectangle by dropping the geometric height to 1.

These days, I usually see if I can use this substitution method first if I want to link a line length to text, and if not, then I use the track-points method.