https://bugs.kde.org/show_bug.cgi?id=479703
Bug ID: 479703
Summary: Expose global Wayland screen offsets of top-left of
all given KDecoration2 geometries for pixel-snapping
with fractional scaling
Classification: Plasma
Product: kwin
Version: master
Platform: Other
OS: Other
Status: REPORTED
Severity: wishlist
Priority: NOR
Component: decorations
Assignee: kwin-bugs-n...@kde.org
Reporter: k...@paulmcauley.com
Target Milestone: ---
Hello,
I am the developer of a C++ window decoration
(https://www.github.com/paulmcauley/klassy). In my window decoration I have
attempted to implement a pixel-snapping algorithm so that lines in icons
(especially horizontal/vertical lines) and other painted items are sharp -
this works on integer scale levels (and by fluke works on scales with a
fractional part of 0.5 because I happen to multiply all my geometries by a
factor of 2), however, it does not work properly on all fractional scales on
Wayland.
This is because I am currently assuming that the QPainter device geometry of
the top-left of the titlebar is a zero pixel boundary reference point
(https://github.com/paulmcauley/klassy/blob/3490b94f721d9cfab4d4cf4691fbfcac8570637d/kdecoration/breezebutton.cpp#L228C2-L228C2)
. However, on Wayland this is not always the case with fractional scaling.
Therefore, to implement pixel snapping properly with fractional scaling on
Wayland, I would kindly request some additions to the KDecoration2 API. Namely,
provide functions returning a QPointF that gives the offset position (call it
e.g. <geometry>ScreenPos() ) in global Wayland co-ordinates from the current
screen position 0,0 to the top-left of a given geometry QRectF. This offset
would not be an integer pixel offset, but rather an offset that would need to
be floating point for Wayland in the same co-ordinate system used by Wayland,
as Wayland co-ordinates are relative to 100% scaling dimensions.
This would be a most welcome additional piece of data to complement the
following <geometry>s provided with KDecoration2, each with their own added
"<geometry>ScreenPos() " offset function:
KDecoration2::DecorationButton::geometry() (this one is the most useful as it
could be used with standalone buttons as well)
KDecoration2::DecorationButtonGroup::geometry()
KDecoration2::Decoration::rect()
KDecoration2::Decoration::titleBar() (potentially useful in case want to draw
on titlebar directly with custom graphics)
KDecoration2::DecorationShadow::innerShadowRect() (could potentially be useful
for drawing automatic sharper window outlines which are currently done as part
of the shadow, though would need this offset available before a shadow is
provided by the decoration).
Thank you,
Paul
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