Re: [Gimp-user] rotate pasted image

[Steve Kinney <admin pilobilus net>]

On 10/26/2016 09:42 AM, alin33 wrote:
> > When you use the word "selection" alone are you talking about the 
> > selection mask or the floating selection?
> >
> > You don't "move" anything in a rotation if the center of rotation is
> > the
> > center of the layer, and this is the default...
> Ok i explain what I'm trying to do.I have a quarter or circle-thats the
> selection-i selected it by color.I paste into this quarter an image-and I want
> to transform it and rotate it inside the quarter without moving the boundaries
> of the quarter selection-the purpose is to find the right look of the pasted
> image because I want to copy the quarter paste it-and finally make a full circle
> mandala.My purpose is to manipulate the pasted image as free as I can-I can move
> it-but i can't rotate it because it rotates the quarter selection also.I don't
> know anything about working with masks.I really hope you have some advits into
> ice for me,because really I already tried evrything.If tou have clear steps of
> what I should do-please replay.thanks.It all began from an ytube video about a
> guy that does digital mandala in photoshop-he pastes it into the quarter of
> circle and manipulate the pasted image in all the possible ways.Is there a way
> to do it in gimp?

What I have done in similar cases:  First I open the source image in the
GIMP.  Then I select the area I want to duplicate, invert the selection
(Select > Invert), and delete everything but the part I want to work
with.  Then I copy the layer, and rotate the copy.  Then I select the
original layer, copy the first layer again, move the new copy to the top
of the layer stack, and rotate the new copy.  I repeat this until I have
completed the circle I am making from copies.

Using only copies of the original layer prevents repeated copy > rotate
from adding noise (transform errors) that would accumulate if copies of
rotated copies etc. were used.

I seem to remember a GIMP script for this, but I can't find the one I am
looking for just now.  However, this should automate everything except
making the initial selection:

http://registry.gimp.org/node/15534

Other things that might be useful in this context:

*  To make the selection, place a vertical line down the center of the
canvas (Image > Guides > New Guide (by percent).  Make a new layer, fill
it with white, and draw a black line right down the center using the
guide.  Then do Layer > Transform > Rotate and rotate the layer as many
degrees as you need for your wedge (360/n.).  Assuming you want to
rotate your mandala parts around the center of the image, add a
horizontal guide centered on the canvas, then use the "lasso" tool to
make your selection as indicated by the guide lines and the line on your
rotated white layer.

*  Instead of deleting the unwanted parts of the source image, do the
selection on your source image, invert it, add a layer mask and fill the
selected area (of the mask) with black.  Proceed as above with the copy
and rotate process.  Advantage:  You can adjust the edges where the
visible parts of the layers meet, by painting on the layer masks with
black to remove visible pixels from the final image, or with white to
restore "deleted" pixels to visibility.  This will however give you a
much larger XCF file.

*  Place a vertical guide down the center of the canvas and free rotate,
move etc. your source image layer until that guide line is right where
you want one of the edges of your pattern's wedges to be.  Select and
add a mask as above.  Then, duplicate the layer and do Layer > Transform
> Flip horizontally.  This will give you a wedge where the edges along
the vertical guide match perfectly.  Merge the 2nd layer down into the
first, duplicate and rotate until your circle is filled.

:o)