Scale watermark to be proportional to image width

Sometimes, it's nice to have the watermark image scaled to some percentage of the target image width - for example, when watermarking a small-ish image (say, 320x200) your watermark image (which may be fine for larger images) may appear to be overwhelmingly large if the watermark is not scaled down.

In another case, a small watermark suitable to use with small images may be barely visible on a very large (1800x1600) image.

So, typically, when I apply a watermark, I scale the watermark to be proportional to the target image.

I realize that not everyone will want this functionality, so, ideally, this would be an optional setting or perhaps one could set a threshold ("Scale watermark to NN % of width if original image width is < $min_width || > $max_width"). Anyway, I'm still thinking about this, any feedback welcome.

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Attached is a proof-of-concept patch against the DRUPAL-4-7 cvs that provides an example of this functionality. I've tested it with 32-bit PNG watermark images with an alpha channel, and it works fine. I've not tested it with other types of watermark source images.

Note: this experimental/proof-of-concept patch 'recycles' the 'percentage' in watermark_form_alter(), so, if you apply this patch, be sure to re-set that value in the admin/settings/image page before uploading any new images.

Examples at:

http://amadorable.com/view-mt-zion-fog-shrouded-valley
http://amadorable.com/view-mt-zion-fog-shrouded-valley?size=button

http://amadorable.com/view-mt-zion-fog-shrouded-valley-panorama
http://amadorable.com/view-mt-zion-fog-shrouded-valley-panorama?size=button

Or, just peruse the galleries at:
http://amadorable.com/image