Thu Jun 20, 2019 3:21 pm
Frank answered indirectly. You can chain mask tools together using their Effect Mask inputs, and they'll Merge. When you connect them, the downstream masks will get a new input that allows you to choose the blend method. If you need a slightly more complex arrangement—for instance, you need to invert some of the masks together prior to combining with another set, you can use the Bitmap tool to tie two branches together.
The Bitmap's own controls affect the Background input, so if you're Subtracting, the Background masks will be subtracted _from_ the masks coming in on the Effect Mask. I like to use Bitmap also to get a single Level and Softness control for a group of masks so they don't have to be adjusted individually if they all represent a single object. It's also useful to be able to Invert a combined matte, since Inverting the masks individually will cause them to merge unpredictably.
Bryan Ray
http://www.bryanray.name
http://www.sidefx.com