Re: [Gimp-user] How to change center point for distorts?

[Steve Kinney <admin pilobilus net>]

On 12/07/2016 05:00 PM, JDawg wrote:
> I'm trying to do a series of WAVE distorts on an image, but it seems the shape
> of the distort is driven by the image size and shape, not the selected area. 
> And the center of the distort is always the center of the image, and again, not
> the center of the selected area.
>
> Is there a way to change the center point of the distortion so that I can create
> a wave distortion, for example, focused on several different points on my
> drawing?

Being able to control the center and radius of wave and similar
distortion filters would be cool, but until the filters are rebuilt for
that there's a work-around.

First, make the canvas big enough that you can move the layer you want
to apply the distortion to into a position where the place you want your
distortion is centered on the canvas.  (Image > Canvas size)  Apply the
filter and there ya go:  Do Image > Fit canvas to layers to get back to
a normal looking situation.

If you want to apply the filter to only part of the image, first
duplicate the layer you want to tweak, then adjust its position as above
and apply the filter to the whole layer.  Move the layer back into
alignment over the original layer, and add a layer mask to it (in the
Layers dock, left click and Add Layer Mask).  Then, with the mask
selected, make sure your Foreground color is white, background color
black in the color selector tool, and select the Gradient tool.  In the
Tool Options dialog, set the gradient mode to Radial.  Click and drag to
make a radial gradient, white to black, centered on the part of the
distortion you want to make visible.

Alternatively, you can make a selection centered on the part of the
layer you are about to distort, do Select > Feather to give the
selection a blended edge, and apply the filter.  Either this or using a
mask will work; I usually prefer using a mask on a duplicate layer,
because that makes the effect adjustable without undoing and duplicating
the whole process of making the distortion.

To get "other than circular" distortion regions via masking, make a
selection with any tool, feather it to blend in with the unaffected
parts of the picture, and drag & drop white onto a black layer mask.  Or
just paint with white on the black mask with an appropriate brush.

To make multiple distortions, repeat the processes describe above as
necessary.

:o)