Vertical filter offset causes bad bounding box calculation

[Bryan Hoyt]

If I set the filter coordinates on an object, the bounding box is offset in the reverse vertical direction. To reproduce:

1. Create an object (eg an ellipse)
2. Open the Filter Editor and create a filter
3. Add an Effect to the filter. "Blend" will do.
4. Make sure the new filter is attached to your object/ellipse.
5. Click on the "Filter General Settings" tab.
6. Set the y coordinate to anything nonzero
7. Observe the incorrect bounding box

To see it really clearly, use your scrollwheel to pseudo-animate the vertical coordinate. You'll see the bounding box move up & down in the wrong direction.

You can see the bug in my attached file.

Reproduced in 0.47 +devel r9500 on Ubuntu 9.10.

[su_v (suv-lp)]

reproduced with Inkscape 0.48+devel r9709 on OS X 10.5.8

While IMHO the selection bounding box is shifted as expected (using the GUI coordinate system, origin in the lower left). the output of the filter effect detaches from the bounding box: clearly visible when setting the y-coordinate to 0.50 or -0.50 (with dimensions set to '1,1'): the bounding box is exactly above of below the filtered region (i.e. the filter effects region is completely outside the selection bbox of the filtered object).

It appears that the coordinates for the filter effect region is calculated in the SVG coordinate system (origin upper left, y down) whereas the calculation of the bbox of the filtered object is based on GUI coordinates (origin lower left, y up).

The tool-tip of the y-coordinate entry box says 'y corner of the upper corners of the filter effects region', which gives a hint that there seems to be some confusion about which of the 2 coordinate systems is used in the GUI for the Filter General Settings: As long as the global switch hasn't been done, I would expect the y coordinate to reference the lower edge of the filter effects region, with y-direction pointing up.

[su_v (suv-lp)]

Does not visibly affect the bbox and filter effects region of the 'Gaussian Blur' filter primitive: the selection bbox stays unmoved, and the x/y coordinates of the Filter General settings are taken as in SVG coordinates.

[su_v (suv-lp)]

No longer reproduced with current trunk (tested with Inkscape 0.48+devel r12185 on OS X 10.7.4).

(Note: trunk has a minor regression (bug #960986) with not updating the selection bbox immediately, but after triggering a manual update, the selection frame matches the filter effects region as defined in the filter editor dialog).