Create Layer Mask from Transparency
In order to automatically convert the transparent areas of a layer into a mask, select Layer > Layer Mask > From Transparency.
In order to automatically convert the transparent areas of a layer into a mask, select Layer > Layer Mask > From Transparency.
Option-Delete (Mac) / Alt-Backspace (Win) + Shift will fill with the currently selected history state and preserve transparency (so that only those pixels that have information in them are filled).
When on a layer, tap the “/” key to toggle the Lock (Transparency, Pixels, Position, or All) option on and off.