issues with filters and transformations

[Pétery Tamás]

Trying to recreate a kaleidoscope effect with filtered objects -no clones this time-.

Found a few issues related to filters:

1. There is a random "banding" on transformed filters.
Horizontal hair lines appear where objects appear from below.

2. Bounding boxes are messed up randomly on the filtered objects.
On some of them it works as expected, on others it is extended with no apparent reason.

3. Moving filtered objects behaves inconsistently with the filter's transformations.
5 out of 6 moves with the filters, but one preserves the filter position regardless translating the object.

Tested on win10 64bit Inkscape 0.92pre4 15278.
I can recall 1st and 3rd are present in 0.91 as well, but the 2nd was new to me.

[su_v (suv-lp)]

> I can recall 1st and 3rd are present in 0.91 as well, but the 2nd
> was new to me.

2nd one is also present in 0.91 (not a regression in 0.92 pre-releases).

[su_v (suv-lp)]

The 2nd issue was exposed with the removal of libnr in r10589 (not reproduced with rev <= 10588, reproduced with rev >= 10589) - whether or not it was an intended change I don't know. It can be observed that unlike with unfiltered objects, the rotation center now (i.e. >= 10589) is fixed relative to the rotated object if the object has a filter effect applied.

[su_v (suv-lp)]

su_v wrote:
> > The 2nd issue (...) whether or not it was an intended change I don't
> know.

On closer inspection, it does make sense AFAIU: the extent of the visual bounding box of the selection is determined by the corners of FER, not by the non-transparent region within the FER (add a Flood filter, and a Merge filter (merging flood before the original last primitive) at the bottom of the filter in use to visualize the FER (filter effects region)).