This filter curls a corner of the current layer or selection into a kind of cornet showing the underlying layer in the cleared area. A new «Curl Layer» and a new Alpha channel are created. The part of the initial layer corresponding to this cleared area is also transparent.
You have four options to select the corner you want to raise.
Horizontal and Vertical refer to the border you want raise.
This is the shadow inside the cornet.
This refers to the outer face of the cornet. Available options are Foreground / background colors, Current gradient, and Current gradient (reversed).
Refers to the visibility of the layer part underlying the cornet. It may be set also in the Layers dialog.