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Details

Type: Bug
Resolution: Done
Priority: P3: Somewhat important
Fix Version/s: 6.2.5, 6.3.0 Beta1, 6.4.0 Beta1
Affects Version/s: 6.2.1
Component/s: Widgets: Widgets and Dialogs
Labels:
None
Environment:
Tested on Windows 10 with dual-screen.

Platform/s:

Windows
Commits:
da6c8b2fc6 (qt/qtbase/dev) da6c8b2fc6 (qt/tqtc-qtbase/dev) 90e5e565f0 (qt/qtbase/6.3) 90e5e565f0 (qt/tqtc-qtbase/6.3) 22f682d620 (qt/qtbase/6.2) 22f682d620 (qt/tqtc-qtbase/6.2)

Description

The "Pick Screen Color" button in QColorDialog permits scanning the colors of the entire screen to pick one of them. But it's not possible to scan colors from a secondary screen (dual-screen, multi-screen...).

The error probably lies in this method:

QColor QColorDialogPrivate::grabScreenColor(const QPoint &p)
{
    QScreen *screen = QGuiApplication::screenAt(p);
    if (!screen)
        screen = QGuiApplication::primaryScreen();
    const QPixmap pixmap = screen->grabWindow(0, p.x(), p.y(), 1, 1);
    const QImage i = pixmap.toImage();
    return i.pixel(0, 0);
}

Suggested fix:

QColor QColorDialogPrivate::grabScreenColor(const QPoint &p)
{
    QPoint localCursorPos = p;
    QScreen *screen = QGuiApplication::screenAt(p);
    if (!screen)
        screen = QGuiApplication::primaryScreen();
  
    if (screen != QGuiApplication::primaryScreen())
    {
        const QRect screenRect = screen->geometry();
        localCursorPos.setX(localCursorPos.x() - screenRect.x());
        localCursorPos.setY(localCursorPos.y() - screenRect.y());
    }

    const QPixmap pixmap = screen->grabWindow(0, localCursorPos.x(), localCursorPos.y(), 1, 1);
    const QImage i = pixmap.toImage();
    return i.pixel(0, 0);
 }

Also, note that the cursor flickers when it moves on the secondary screen. No fix suggestion for that part. Might be somehow related to https://bugreports.qt.io/browse/QTBUG-43448