[Gimp-developer] transparent transformation preview

[David Gowers]

Hi Patrice,

On Sat, Mar 1, 2008 at 12:39 PM, Patrice Poly <p.polypa at gmail.com> wrote:
> Hello
>
>  I have searched a lot about this, and couldn't find anything apart a few lines
>  in an old summer of code page, and in this old webpage :
>  http://www.re.org/tom/computer/gimp/index.html#preview
>  unfortunately this patch only applies to 2.3
>
>  this is why I allow myself to post here as a feature wish, even though I am
>  absolutely not a coder.
>
>  I am using GIMP every single day for my 3D texturing work, and i have to blend
>  together parts of photographies in an interactive way.
>  Parts need to be lined accurately so that you don't create blur in the
>  blending areas.
>  ( someone told me Hugin does it perfectly, but at a first glance, it seems to
>  involve complex settings and a lot of click work before it computes a
>  solution, when you just need to move things on the fly and see how it goes .
>  Hugin seems to be more suitable for assembling large images together than a
>  lot of little parts )
>
>  As GIMP is now, you need to move/scale/rotate/shear/perspective a selection or
>  a layer, apply transformation, check if it lines good, undo, transform again,
>  check, etc, because the preview always turn to totally opaque , whatever the
>  layer opacity is.
>
>  Having a little slider to set the preview mode/transparency would be a real
>  enhancement for this kind of workflow.
>  Another clean solution would be that the preview simply follows the active
>  layer mode/opacity .

In order to have a genuinely clean solution, I believe that GEGL needs
to be integrated for layer compositing. Because
the main issue here is that, when you overlay an preview of N opacity
over a layer of N opacity, the appearance is that of
> N opacity -- ie. such a preview is still not accurate. It's the same effect that occurs when you draw a dab of paint at 50% opacity and then draw another over the top -- the result is more than 50% opaque.
What needs to happen is, the preview is composited onto the layer with
100% opacity, before that layer is composited onto the one below. This
is rather tricky and without a graph-based image display, it is
difficult to do in a non-kludgey way.
>
>  I have read about Iwarp as a tool, that combined with a transparent transform
>  preview would turn GIMP into a fantastic texturing tool.
>
>
>  I have no clue how difficult it can be to code this, but I hope the developers
>  of GIMP can find an interest in this.
>
>
>  With all my thanks for all the work done,
>
>  regards
>
>  patrice poly
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