Broken feComposite when using BackgroundImage
Migrated from https://bugs.launchpad.net/inkscape/+bug/1438926 (see comments for regression window and workaround)
Example File
The attached file shows two objects. The one on top has an feComposite filter applied (mode "arithmetic" with k=0,1,1,0) which is designed to mimic an Additive blend mode (result = source + background).
In Inkscape, the object displays as though unfiltered. In the GitLab thumbnail, the object is completely invisible (at least on Firefox).
Expected Output
Actual Output
More Info
I first learned this trick from Kiirala on this 11-year-old feature request: https://bugs.launchpad.net/inkscape/+bug/298831
I have an enormous archive of files created with older versions of Inkscape using this technique, which was working 100% fine when they were created. (I have raster exports to prove it.) However, sometime after 2010 it stopped working, and now applying the feComposite filter has absolutely no effect on the image. Even opening the same old files unchanged, the filtered objects look opaque as though not filtered. (Unfortunately I didn't have time to look into it until now.)
This is obviously a problem for me in reading and using my archived files with 100% fidelity. I can't just slap on a Screen blend mode instead and get the same result.
Is there any way I can reproduce the desired output with modern Inkscape? Any thoughts are appreciated.
Thank you!
Currently Failing On:
- MacOS 10.14.6 with Inkscape 0.91 r13725 on XQuartz
- MacOS 10.14.6 with Inkscape 0.92.2 5c3e80d3 on XQuartz
- Fedora 24 with Inkscape 0.91 r13725
(Yes, my Fedora machine is too old.