weird black rectangles which break certain sprites

[Robo Dodo]

In two files of mine I've had problems with weird rectangles covering my images.
They also seem to corrupt the images that I'm trying to export.
I've added a short video in which the bug can be seen and it's effect on exported images.

[su_v (suv-lp)]

Please attach a test case (Inkscape SVG file) to the bug report to allow further investigation of the reported issue, thank you.

[su_v (suv-lp)]

... and please also add information about OS/platform and Inkscape version to the bug description.

[Robo Dodo (robododo)]

Here's one of the affected documents. If the objects with the shadows were copy pasted into a new document the problem also occurred. We've found that the problem has something to do with the shadows of certain objects.
After deleting them the problem was fixed.

[su_v (suv-lp)]

Object triggering the rendering artifacts:
path6629, path5971, path5971, path6043

They all reference the colors of the black-to-transparent gradient 20164-7, and use specific gradientTransforms like

matrix(0,0.02492168,-8.3771866,0,3756.8234,-488.45524)
matrix(0,0.02492168,-8.8644754,0,4041.0118,-443.92787)
matrix(0,0.02743499,-4.5080969,0,1481.4226,-420.64502)
matrix(0,0.02293027,-2.0801871,0,54.4486,-411.21809)

Removing the paths, or changing their fill to a solid color (for testing) makes the artifacts go away. When the gradients are re-applied after that, they will no longer expose these rendering artifacts because the gradientTransform will be optimized into the coordinates of the gradient vector.

These artifacts with transformed gradients using very small dimensions has been reported before and is tracked in
* Bug #1594988 “Object with gradient causes black bar-shaped artifacts with certain zoom”
  https://bugs.launchpad.net/inkscape/+bug/1594988