I am uncertain about what you are attempting so you will forgive me if
my response is completely off-base. Firstly, layermasks "choose" (or
blend) between two images, the layer to which it is attached AND
"everything underneath". Your description is confusing because you don't
really specify what is to be blended with the current layer. By having
only one layer visible at a time, the "everything underneath" will be
transparent; which may be precisely what you intend (or perhaps you will
put something there after your positioning is complete?).

Assuming that you are only concerned with the positioning of the mask
relative to a single image (a single layer), I would propose that a
channel mask might be a more appropriate solution. Taking, for example,
several different layers over which you wish to place a text label:
create your text and perform an Alpha to Selection, Invert your
selection, perform "Select->Save To Channel", and make the newly created
channel visible. (You can change the color and opacity of the channel
mask if you wish, or leave it at 50% opacity.) Once you have done this,
you can individually select your layers and move/transform them to see
how the end result would appear. 

When you have the layer positioned as you like, you should hide your
channel mask, perform a Channel To Selection (using the button at the
bottom of the Channels dialog), and add a layermask to the appropriate
layer (initializing it to the Selection). At this point, I am unclear
how you should proceed because I don't know if you wish the mask (the
text label in the example) to be a transparency or something else. If a
transparency, you are basically finished; if an image (or a solid color,
gradient, pattern, etc) then put that image on a visible layer beneath
the one with your layermask.

David Marrs wrote:

> I've been trying to accomplish some things with layer masks that I don't
> believe are currently possible. Please correct me if they are. I've been
> thinking about how to solve the problem and thought I'd ask the
opinion of the
> community before posting a feature request to bugzilla.
> I want to apply the same layer mask to a number of stock photos. In
this case
> the mask is text but it could be anything. I want to get the best
image for the
> mask and this means not only trying different photos but also aligning
> photos for best composition.
> As far as choosing from a selection of images goes, the easiest thing
in my
> mind would be to create one layer mask and then paste it to other
layers. Then
> I'd switch visibility between them to see which I prefer. Unfortunately,
> selecting the mask, hitting copy and then selecting a new layer and
> paste doesn't work; the mask gets added as a floating selection with its 
> position changed and when I anchor it, it is merged directly into the
> layer instead of being applied as a mask.
> The other problem comes when I try to reposition the layer being
masked. The
> idea is to apply the mask and then establish the best position for the
> beneath it by using the move tool. Unfortunately, moving the layer
also moves
> the mask and I don't seem to be able to move one independently of the
> In summary, masks seem to be dependant on their layers and can't easily be
> moved either within or between layers. I'd like it if layer masks were
> independent of one another to make such flexibility possible. Is this a
> desirable change? Are there side effects of this that cause problems?
Is it
> already possible?

"It is amazing what you can accomplish if you do 
not care who gets the credit." -- Harry S. Truman

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