SS.3.02 Line Taper Expression

I created this expression setup as a work around during a live brief (logo animation). Many motion designers will agree that the tool After Effects is missing the most is one that will taper a stroke like illustrator does:


It would be ideal to have a small script that can create lines that follow a path with a range of profiles for the user to choose from. In my work around, I used expressions to create a ‘line’ with the uniform taper profile. Much like my other expression this works off of the index of a layer and requires multiple (50 in this case) copies of layers so that the effect will work.

The main line drawn is in fact the entire motion path of the animation, so forward planning is required here.



The line is given a stroke with the Trim Paths effect applied. The start value of Trim Paths is keyframed, this is the driving force of the animation. The end value is given an expression, parenting it to the start value but with a ‘delay’ (an offset) of a value which is dictated by its index.

delay = (index/4);

content(“Shape 2”).content(“Trim Paths 1”).start-0.1-delay;

The divider value used in line 1 (4 in this case) will change how long the line taper is. If I develop this into a script, this value will be open for the user to edit. The 0.1 in line 2 is just an offset and will remain a constant.

Since each line is longer than the last this provides us with increments, allowing for the stroke width to also be reduced in incrementally along the line.

The layer with an index of 1 returns this line:


The layer with an index of 47 returns this line:


The final animation looks like this:


If I am to develop this into a usable script, I will need to adjust the incrementation of the lines so that they are all the same length but appear at different points along the path. A profile that gets thinner and then thicker again for example, would not work with the current setup.


Author: Pip Williamson

Pip // Animator & Motion Designer

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