[Gimp-developer] Using drawables with preview

[triffid at oink.co.uk]

Hi there,

I've been experimenting with GIMP plug-ins. At present, I'm following 
the tutorial's example:- 
http://developer.gimp.org/writing-a-plug-in/3/myblur5.c

My question is this; "How can I use GimpDrawable-functions on a preview 
window without modifying the original image?"

To clarify:-
In the example, blur() is passed a Drawable (from the main image 
itself), and uses it to make an "input" GimpPixelRgn (rgn_in). The raw 
pixel info from rgn_in is then processed and written as more raw pixels, 
to a different GimpPixelRgn, rgn_out.

Rgn_out forms the basis of the preview:
gimp_drawable_preview_draw_region (GIMP_DRAWABLE_PREVIEW (preview), 
&rgn_out)

However, I want to annotate the PREVIEW (*without* modifying the 
original image's drawable) using gimp_pencil(). That requires a 
GimpDrawable, but rgn_out- i.e. the processed pixels which are used to 
create the preview's contents- is in GimpPixelRgn format. How do I draw 
on the output window?

Getting the Drawable associated with the preview widget via
gimp_drawable_preview_get_drawable()
simply returns the main image's drawable, which we already have. Drawing 
to this (a) messes up the *original* image, and (b) has no effect on the 
preview (since that is taken from the processed rgn_out data).

Any help would be appreciated, thank you.

- triffid at oink.co.uk


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