Checkerboard background no longer blends with background color (rev >= 14821)

[su_v]

The checkerboard background for Inkscape's canvas (introduced in rev 14539, tracked in bug #397723) originally blended with the page background color (and still does with lp:inkscape/0.92.x).

During the refactoring of the canvas drawing for GTK3 during the Hackfest 2016 this color blending broke, and the background color for the canvas is visibly only in effect if the checkerboard background is disabled.

Steps to reproduce:
1) launch inkscape trunk (default new prefs, default new document)
2) open Document Properties > Page
3) enable checkerboard background
3) click on the button to edit the background color
4) adjust the background color e.g. to blue (#0000FF), with 50% alpha (127).

Expected result:
The partially transparent background color is blended over the checkerboard pattern.

Actual result:
The checkerboard background does not change.

Reproduced with Inkscape 0.92+devel r15467 on Ubuntu 14.04.5 LTS.

Notes:
* The reported issue only affects trunk lp:inkscape (the refactoring of the canvas had been reverted in the stable release branch lp:inkscape/0.92.x).
* Based on tests with archived trunk builds (on OS X 10.7.5):
- not reproduced with rev <= 14820;
- reproduced with rev >= 14821;
the reported issue was likely exposed with the changes in rev 14821:
«Move background drawing to SPCanvas to avoid temporarily drawing an incorrect background. #Hackfest2016»
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/14821

[jazzynico (jazzynico)]

Regression confirmed on Xubuntu 16.04, lp:inkscape rev. 15467.

[Jonathan Hofinger (jhofinger)]

This can't be replicated anymore in current master (but was there in 1.0beta2) so I'm closing it.

If it occurs again, feel free to reopen in Gitlab.

Closed by: https://gitlab.com/jhofinger