https://bugs.kde.org/show_bug.cgi?id=408225
Bug ID: 408225
Summary: Canvas itself becomes transparent with transparent
pixels, showing what is behind the Krita window
Product: krita
Version: 4.2.0
Platform: Kubuntu Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: OpenGL Canvas
Assignee: krita-bugs-n...@kde.org
Reporter: captains...@gmail.com
Target Milestone: ---
Created attachment 120509
--> https://bugs.kde.org/attachment.cgi?id=120509&action=edit
Screenshot showing issue; note the desktop visible through the transparent
orange areas
Any pixels that are transparent and show the canvas (that is, show the
checkerboard "transparent" pattern and would have an alpha of less than 1.0 if
ultimately exported) seem to be showing what's behind the Krita window itself.
That is, the desktop (or whatever else is there) becomes visible through the
transparent areas.
I stumbled across this when I noticed the antialiased edges of black Bezier
curve vectors didn't look black on-screen. When I zoomed in, I saw the default
Kubuntu wallpaper peeking out through the enlarged, transparent pixels. I
tried it with other transparencies, and sure enough, they all showed my desktop
behind the transparent areas.
Curiously, if there's no pixel data at all in a given region (or the pixels are
completely transparent), that area is NOT transparent to the desktop, and just
the plain checkerboard is visible.
If I turn off Canvas Graphics Acceleration in the settings, the problem goes
away, leading me to believe this is something to do with OpenGL.
STEPS TO REPRODUCE
1. Create a new image.
2. Draw a filled, opaque square by whatever means you wish.
3. Set the layer on which the square is to anything less than 100% Opacity.
OBSERVED RESULT
The desktop is visible through the transparent square and the transparency
checkerboard.
EXPECTED RESULT
Only the checkerboard should be visible through the transparent square; the
Krita canvas itself should not be transparent.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kubuntu 18.04, running Linux 4.15.0-50-generic from Ubuntu
packages
(available in About System)
KDE Plasma Version: 5.12.7
KDE Frameworks Version: 5.47.0
Qt Version: 5.9.5
ADDITIONAL INFORMATION
This problem shows up on both my desktop and my laptop. The desktop has a
GeForce GTX 970, and the laptop has the mobile version of same. Both are
running the same version of Kubuntu with the same KDE Plasma, Frameworks,
Krita, and Qt versions.
In the attached screenshot, you can see a diagonal yellow line from the default
Kubuntu 18.04 wallpaper behind the transparent orange area ("Curtains Fore" in
the layer list, currently set to 34% opacity for demonstration), as well as the
icons for Inkscape and GKrellM in a folder widget on the desktop. Areas with
no pixel data just show the checkerboard.
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