create_mask

Create a layer mask for the specified layer.

This procedure creates a layer mask for the specified layer. Layer masks serve as an additional alpha channel for a layer. Different types of masks are allowed for initialisation:

• white mask (leaves the layer fully visible);
• black mask (gives the layer complete transparency);
• the layer's alpha channel (either a copy, or a transfer, which leaves the layer fully visible, but which may be more useful than a white mask);
• the current selection;
• a grayscale copy of the layer;
• or a copy of the active channel.

The layer mask still needs to be added to the layer. This can be done with a call to add_mask.

create_mask will fail if there are no active channels on the image, when called with 'ADD-CHANNEL-MASK'. It will return a black mask when called with 'ADD-ALPHA-MASK' or 'ADD-ALPHA-TRANSFER-MASK' on a layer with no alpha channels, or with 'ADD-SELECTION-MASK' when there is no selection on the image.

Parameters:

this	The layer to which to add the mask.
mask_type	The type of mask.

Returns:

The newly created mask.