Could you elaborate on how you would like to create a mask or alpha channel from shape layers?
Using a shape as a mask or an alpha channel is already possible in AE. There are several possible methods, and I'll outline some of them below, but please let us know what you'd like to see that is different.
Method 1: Copy a Beizer shape path to a mask path
This only works with Bezier shape paths. If you create a parametric shape path (rectangle, ellipse, star, etc.), right click on the path (e.g. Rectangle Path 1) and choose Convert to Bezier Path.
Twirl open the shape's Path group (e.g. Path 1) and select the Path property.
Edit > Copy or Cmd/CTRL + C
Select the layer you want to add a new mask to, and draw a new mask on it. It doesn't matter what the mask looks like, just draw something.
Twirl open the Masks > Mask 1 property.
Select the Mask Path property.
Edit > Paste or Cmd/CTRL + V
Method 2: Link a Bezier shape path to a mask path using expressions.
Like Method 1, this works because under the hood, both a mask path and a Bezier shape path use the same Bezier path data. It also only works with Bezier shape paths, so you need to Convert to Bezier Path if you started with a parametric shape.
Twirl open both the shape layer Path group on your shape layer and the Mask 1 group on the layer you want to mask, so that you can see both the shape Path and Mask Path properties. (You can also use the Search bar in the Timeline panel to search for Path.)
Click on the pick whip icon in the Parent & Link column next to the Mask Path property and drag it over the shape Path property and release the mouse. (If Parent & Link column isn't visible, right-click on any other column header in the Timeline panel and select it.)
Simple, no? You can look at the expression created on the Mask Path property to see that AE allows paths to be referenced. You can also use expressions to create a path from scratch, but that's a different tale for a different day.
Method 3: Set the shape layer as a track matte for the target layer.
Place the shape layer immediately above the target layer in the Timeline layer stack.
In the Track Matte (aka TrkMat) column, set the track matte to Alpha Matte "Shape Layer 1" (the name of the shape layer may differ, of course).
Method 4: Use the Set Matte effect to generate an alpha matte
Apply the Set Matte effect (found in the Channel category of effects) to the target layer.
In the controls for the effect, change the Take Matte From Layer option to the shape layer.
For each of these methods, there are unique advantages, but they'll all accomplish what you've requested.
Thank you for filing this request.
Could you elaborate on how you would like to create a mask or alpha channel from shape layers?
Using a shape as a mask or an alpha channel is already possible in AE. There are several possible methods, and I'll outline some of them below, but please let us know what you'd like to see that is different.
Method 1: Copy a Beizer shape path to a mask path
This only works with Bezier shape paths. If you create a parametric shape path (rectangle, ellipse, star, etc.), right click on the path (e.g. Rectangle Path 1) and choose Convert to Bezier Path.
Twirl open the shape's Path group (e.g. Path 1) and select the Path property.
Edit > Copy or Cmd/CTRL + C
Select the layer you want to add a new mask to, and draw a new mask on it. It doesn't matter…
David Cummins
