Use absolute values for watermark size and location

[wohler]

Sizing and locating watermark text seems more difficult than it should be.

I have discovered that that the scale on > advanced options > smaller image border > marker height allows me to use the same scale for all aspect ratios and achieve a constant text height. However, I still have to have separate presents for each aspect ratio to account for different x and y offsets, and if I have to move the watermark to a different location, I have to tweak the offsets again.

I'd love to be able to set the absolute height of a textual watermark and be able to anchor its outer corner in such a way so that a single watermark present would work for portrait, square, and landscape images for text of any length, and would not require additional location tweaking if the location (upper left, lower right, and so on) was changed.

For example, let's say I set the text height to 20 pixels and the distance to corner of 20x20 pixels.

Then, no matter how wide the text is, the height would always be the same. No matter the size of the image, the height would always be the same. If I leave the default location in the lower right-hand corner, the lower right-hand extent of the text would be 20 pixels from the right edge and 20 pixels from the bottom edge. If I selected the upper right-hand corner, the upper left-hand extent of the text would be 20 pixels from the left edge and 20 pixels from the top edge.

In other words, no matter the length of the text, the size of the image, or the location of the watermark, I would not have to tweak the watermark size and location settings.

And then I could have a single preset with these settings.

A related issue is #12813.

[ralfbrown]

All of darktable's modules use resolution-independent coordinates - that's what allows presets and styles to be applied to any image. But all bets are off if you want to move things around from image to image....

It should be possible to create an SVG file which will force the text to a certain fraction of the image height, but absolute pixel sizing and positioning won't be possible without re-architecting things.

[wohler]

Thanks! Now that you mention it, pixels probably isn't what I want since the resolution can vary.

If we were to, say, change "pixels" to "mm" in this request, would that then be doable?

[ralfbrown]

If you assume a fixed print size, "mm" is just the current resolution-independent coordinate. If you want the "mm" at a fixed PPI so that print size scales with image resolution, it's just a roundabout way of specifying pixels.

[github-actions]

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