https://bugs.kde.org/show_bug.cgi?id=526317
Bug ID: 526317
Summary: WheelHandler: Alt+wheel scrolls vertically on Wayland
because Qt now swaps the axes too
Classification: Frameworks and Libraries
Product: frameworks-kirigami
Version First unspecified
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: Not decided
On Wayland, Alt+wheel over a Kirigami-handled scroll view scrolls vertically
instead of horizontally. This affects any Qt Quick Controls ScrollView in the
org.kde.desktop style, whose Kirigami.WheelHandler scrolls the flickable.
Shift+wheel pages vertically, as intended.
The axes are swapped twice:
1. Since QTBUG-124807 (qtwayland commit a1452b95f7, "Make wheel operations
compatible with xcb"; in Qt 6.8 and backported to 6.7.2, 6.5.6, 6.2.13 and
5.15.18), Qt's Wayland platform plugin swaps angleDelta and pixelDelta when Alt
is held, as the xcb plugin always has.
2. WheelHandler::scrollFlickable (src/wheelhandler.cpp, around line 538 in
6.30.0) swaps them again when Alt is held. It only skips that on xcb:
// HACK: Only transpose deltas when not using xcb in order to not conflict with
xcb's own delta transposing
if (modifiers & m_defaultHorizontalScrollModifiers && qGuiApp->platformName()
!= QLatin1String("xcb")) {
On Wayland the event arrives already sideways, and the handler turns it back to
vertical.
Steps to reproduce:
1. In a Wayland session, run this with QT_QUICK_CONTROLS_STYLE=org.kde.desktop
qml6 test.qml:
import QtQuick
import QtQuick.Controls
ApplicationWindow {
width: 400; height: 300; visible: true
ScrollView {
anchors.fill: parent
Flickable {
contentWidth: 2000; contentHeight: 2000
Grid {
columns: 20
Repeater { model: 400; Rectangle { width: 100; height: 100;
color: index % 2 ? "steelblue" : "lightgray" } }
}
}
}
}
2. Scroll with the wheel while holding Alt.
Observed: the content scrolls vertically.
Expected: it scrolls horizontally, as it does with the xcb platform and in Qt
Widgets apps on Wayland.
Logging the QWheelEvents the window receives shows a plain notch arriving as
angleDelta (0, -180), and with Alt held as (-180, 0) with AltModifier set, so
Qt has already swapped it. I got the same result under a nested KWin (input
sent through org_kde_kwin_fake_input) and under sway, so it doesn't depend on
the compositor.
Suggested fix: also skip the swap on Wayland (platformName() starting with
"wayland") when running on a Qt that has the QTBUG-124807 fix.
Versions: Kirigami 6.30.0, qqc2-desktop-style 6.30.0, Qt 6.11.2, KWin (nested,
--virtual) and sway 1.x, Arch Linux.
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