(trunk) Color Matrix 'adjust constant component RGB values' (last column) has no affect when applied to source alpha

[Splex]

On Inkscape stable, it is possible to add a constant value to the RGB channels when applying a 'Color Matrix' filter to 'source alpha.'
In trunk, the RGB rows of the last column have no effect on the output. Only the alpha (last row) works as intended.

Attached is an example:
The upper gradient is gray to transparent (#808080FF -> #80808000) with a Color Matrix filter with 'source alpha.' The matrix is:
1 0 0 0 1
0 1 0 0 0
0 0 1 0 0
0 0 0 1 0
(A constant value of 1 is added to red output channel)

The lower gradient is red to transparent (#FF0000FF -> #FF000000)

Intended Result:
On stable, the upper gradient appears like the lower.

Trunk:
The upper gradient is rendered as black fading to 100% transparent. The constants on the color matrix have no effect on the RGB channels.

[su_v (suv-lp)]

Not reproduced with Inkscape 0.48.2 and 0.48+devel r10325 (before the merge of cairo-rendering) on Mac OS X 10.5.8 (i386)
Reproduced with 0.48+devel r10330 and later revisions (up to current r10752).

Based on comparisons with other SVG renderers (Squiggle (Batik 1.7), Opera 11.52, recent Chromium snapshot (r111116)), Inkscape's new renderer seems to be wrong, and the old renderer does display such feColormatrix filter effects correctly.

[jazzynico (jazzynico)]

Reproduced on Windows XP, Inkscape trunk revision 11652.

[jazzynico (jazzynico)]

Also affects filters applied to background alpha.

Something wrong with ink_cairo_extract_alpha(), in src/display/cairo-utils.cpp?

[Jonathan Hofinger (jhofinger)]

Hi - thanks for reporting this bug, I've manually migrated it to Inkscape's new bug tracker on GitLab, and closed it here.

Please feel free to file new bugs about the issues you're seeing at http://inkscape.org/report.

Moved to: https://gitlab.com/inkscape/inbox/issues/2013
Closed by: https://gitlab.com/jhofinger