Re: [gthumb-list] Writing an extension - how to overlay metadata on images?

[Phil Ashby <phil gnome ashbysoft com>]

On 01/03/2019 20:45, Paolo Bacchilega via gthumb-list wrote:
> Il 01/03/19 19:11, Phil Ashby ha scritto:
> > My question for the list:
> >
> > How /should/ I go about overlaying metadata on loaded images? Where 
> > and how should I intercept the rendering process (it feels like there 
> > should be hooks registered but I cannot find any)?
>
> A possible way is to use the gth-browser-activate-viewer-page hook, 
> inside the hook function you have to check if the current viewer page is 
> of type GTH_IMAGE_VIEWER_PAGE, as an example see the function 
> ir__gth_browser_activate_viewer_page_cb in 
> extensions/image_rotation/callbacks.c.
>
> If it's a GTH_IMAGE_VIEWER_PAGE, you can use 
> gth_image_viewer_page_get_image_viewer to get the image viewer widget 
> and then use gth_image_viewer_add_painter to add a function that will 
> used to paint something over the image, as an example see the 
> paint_comment_over_image_func in 
> extensions/image_viewer/gth-image-viewer-page.c.
>
> A painter function gets a cairo context, so from there you can just use 
> cairo to paint over the image.
>
> - Paolo

Many thanks for the advice Paolo, after a bit more experimenting with 
how all the various scaling and scrolling co-ordinates work, I now have 
a better solution using this approach, which fixes my issues with 
scaling marker text/lines and reloading them all the time. It should 
also work with all image types :)

Thanks again,
Phil.