A layer mask is drawn as a polygon in VPT's mask editor and saved as a black-and-white PNG

VPT’s mask editor lets you draw a freeform polygon mask for a layer. Open it with the ‘editor’ button in the active tab; the default mask is a triangle you reshape. Click between existing points to add points, drag a point to move it, and select a point (it turns red) then press delete to remove it. A ‘circle’ option gives a circular mask with an adjustable diameter, and applying blur before saving gives a soft edge more efficiently than the maskblur parameter afterwards. Naming and saving writes a black-and-white 1024×768 PNG into the project’s mask folder; you can also create or refine masks in GIMP/Photoshop as long as the file is a 1024×768 PNG placed in that folder. Available masks appear in the layer’s mask menu.

Examples

Draw a mask isolating a triangular wall panel, add a small blur, name it and save; it appears in the mask menu and can be applied to any layer covering that area.

Assessment

Walk through creating a polygon mask for a layer from opening the editor to applying the saved mask. Where is the mask file stored and what format/size is it?