Buggy graphics when using blend modes on transparent backgrounds
Steps to create file
- open Inkscape (must be older version, e.g. 0.92.4 since 1.0 uses css blend modes instead of filters)
- create a new document
- create any object (confirmed to happen with: circles, rectangles, paths)
- make it transparent (either using the Opacity slider in the layer windows or using the alpha channel under Fill and Stroke)
- create a new layer above the current one
- create any object on this layer
- set the blend mode of the upper layer to anything other than Normal
Alternatively, you can also use the Filters -> Fill and Transparency -> Blend filter with the default settings.
The effect is also visible when opening the Inkscape SVG in some other image viewers. (tested with Gimp and gThumb)
What happened?
You can see a rectangular darkened area (the filter region of the layer) on the lower layer.
When dragging the object on the upper layer over the lower layer, it leaves a trace that is removed when zooming in or out, or interacting with the objects in any other way. The effect gets less intense when you make the lower layer more transparent. The transparency of the upper layer doesn't matter, you can make it fully transparent and the artifact will still be visible. The effect is only visible inside the boundaries of the lower object.
What should have happened?
Only the shape above should be multiplied, and nothing outside it should be multiplied.
Inkscape Version and Operating System:
- Inkscape Versions: Inkscape 0.92.4 (5da689c313, 2019-01-14), 1.0beta1 (fe3e3069, 2019-09-17)
This has been tested on two devices. Device 1:
- Operating System: Ubuntu 19.04 (using the proprietary Nvidia Drivers)
- Graphics Card: Nvidia GeForce 1060
Device 2:
- Operating System: Win10 Pro 1903, OS build 18362.418
- Graphics Card: Built-in Intel Graphics!