fix: restore multi-monitor screenshot capture in Qt6#405
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Qt6's QScreen::grabWindow(0) captures only the screen it belongs to, unlike Qt5's QDesktopWidget-based approach which grabbed the full X11 virtual desktop. This broke fullscreen and area capture on multi-monitor setups — the image always showed the primary screen content regardless of which monitor the cursor was on. Fix by iterating all QScreens, grabbing each one individually, and compositing them onto a canvas sized to the full virtual desktop. Translate all coordinates relative to the virtual desktop origin so per-monitor crop and selection capture work correctly when monitors are arranged with negative Qt logical coordinates. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Problem
After the Qt6 migration, screenshot capture on multi-monitor setups is broken.
captureAllMonitors(),captureFullscreen(), andcaptureSelection()all produceincorrect results — the image shows only the primary screen content regardless of
which monitor the cursor is on.
Root cause: Qt6's
QScreen::grabWindow(0)captures only the screen it belongs to,whereas Qt5's
QApplication::desktop()->winId()referred to the X11 root window whichspans the full virtual desktop. The single-line change in the Qt6 migration
(
grabWindow(desktopWinId, ...)→grabWindow(0, ...)) silently broke this behavior.Additionally,
QScreen::geometry()returns Qt logical coordinates which can benegative (e.g. a monitor to the left of the primary has negative X). The old code
passed these coordinates directly to
QImage::copy()which uses pixel coordinates —a mismatch that causes wrong crops.
Fix
captureAllMonitors(): iterate allQGuiApplication::screens(), grab each onewith
s->grabWindow(0), and composite onto a canvas sized to the full virtual desktopcaptureFullscreen()andcaptureSelection(): translate screen geometry relativeto the virtual desktop origin before cropping
Tested on a two-monitor setup (primary 2560×1440 + secondary 1920×1200) on X11/Qt6.