Windows: Fix QColorDialog's live updates while picking outside color

Microsoft's SetCapture() doesn't work on windows owned by other processes,
so instead we use a timer. This is the same approach as used by qttools/src/pixeltool.

The mouse move approach however is more elegant and doesn't hammer the CPU with
QCursor::pos() calls when idle. For this reason the workaround is Q_OS_WIN only.

Task-number: QTBUG-34538
Change-Id: I40a6f7df5bf2a3a29ade8fe4a92f5b5c4ece7efb
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

3 files changed, 48 insertions, 5 deletions

diff --git a/src/widgets/dialogs/qcolordialog.cpp b/src/widgets/dialogs/qcolordialog.cpp
index f04e5b9ea6..882bb999fb 100644
--- a/src/widgets/dialogs/qcolordialog.cpp
+++ b/src/widgets/dialogs/qcolordialog.cpp
@@ -57,6 +57,7 @@
 #include "qdialogbuttonbox.h"
 #include "qscreen.h"
 #include "qcursor.h"
+#include "qtimer.h"
 
 #include <algorithm>
 
@@ -1577,6 +1578,11 @@ void QColorDialogPrivate::_q_pickScreenColor()
 #else
     q->grabMouse();
 #endif
+
+#ifdef Q_OS_WIN
+    // On Windows mouse tracking doesn't work over other processes's windows
+    updateTimer->start(30);
+#endif
     q->grabKeyboard();
     /* With setMouseTracking(true) the desired color can be more precisedly picked up,
      * and continuously pushing the mouse button is not necessary.
@@ -1600,6 +1606,9 @@ void QColorDialogPrivate::releaseColorPicking()
     cp->setCrossVisible(true);
     q->removeEventFilter(colorPickingEventFilter);
     q->releaseMouse();
+#ifdef Q_OS_WIN
+    updateTimer->stop();
+#endif
     q->releaseKeyboard();
     q->setMouseTracking(false);
     lblScreenColorInfo->setText(QLatin1String("\n"));
@@ -1782,6 +1791,10 @@ void QColorDialogPrivate::initWidgets()
     cancel = buttons->addButton(QDialogButtonBox::Cancel);
     QObject::connect(cancel, SIGNAL(clicked()), q, SLOT(reject()));
 
+#ifdef Q_OS_WIN
+    updateTimer = new QTimer(q);
+    QObject::connect(updateTimer, SIGNAL(timeout()), q, SLOT(_q_updateColorPicking()));
+#endif
     retranslateStrings();
 }
 
@@ -2196,18 +2209,37 @@ void QColorDialog::changeEvent(QEvent *e)
     QDialog::changeEvent(e);
 }
 
-bool QColorDialogPrivate::handleColorPickingMouseMove(QMouseEvent *e)
+void QColorDialogPrivate::_q_updateColorPicking()
 {
-    // If the cross is visible the grabbed color will be black most of the times
-    cp->setCrossVisible(!cp->geometry().contains(e->pos()));
+#ifndef QT_NO_CURSOR
+    Q_Q(QColorDialog);
+    static QPoint lastGlobalPos;
+    QPoint newGlobalPos = QCursor::pos();
+    if (lastGlobalPos == newGlobalPos)
+        return;
+    lastGlobalPos = newGlobalPos;
 
-    const QPoint globalPos = e->globalPos();
+    if (!q->rect().contains(q->mapFromGlobal(newGlobalPos))) // Inside the dialog mouse tracking works, handleColorPickingMouseMove will be called
+        updateColorPicking(newGlobalPos);
+#endif // ! QT_NO_CURSOR
+}
+
+void QColorDialogPrivate::updateColorPicking(const QPoint &globalPos)
+{
     const QColor color = grabScreenColor(globalPos);
     // QTBUG-39792, do not change standard, custom color selectors while moving as
     // otherwise it is not possible to pre-select a custom cell for assignment.
     setCurrentColor(color, ShowColor);
     lblScreenColorInfo->setText(QColorDialog::tr("Cursor at %1, %2, color: %3\nPress ESC to cancel")
                                 .arg(globalPos.x()).arg(globalPos.y()).arg(color.name()));
+}
+
+bool QColorDialogPrivate::handleColorPickingMouseMove(QMouseEvent *e)
+{
+    // If the cross is visible the grabbed color will be black most of the times
+    cp->setCrossVisible(!cp->geometry().contains(e->pos()));
+
+    updateColorPicking(e->globalPos());
     return true;
 }
 
diff --git a/src/widgets/dialogs/qcolordialog.h b/src/widgets/dialogs/qcolordialog.h
index d23254a2b2..b06da2ab13 100644
--- a/src/widgets/dialogs/qcolordialog.h
+++ b/src/widgets/dialogs/qcolordialog.h
@@ -116,6 +116,7 @@ private:
     Q_PRIVATE_SLOT(d_func(), void _q_newCustom(int, int))
     Q_PRIVATE_SLOT(d_func(), void _q_newStandard(int, int))
     Q_PRIVATE_SLOT(d_func(), void _q_pickScreenColor())
+    Q_PRIVATE_SLOT(d_func(), void _q_updateColorPicking())
     friend class QColorShower;
 };
 
diff --git a/src/widgets/dialogs/qcolordialog_p.h b/src/widgets/dialogs/qcolordialog_p.h
index af3ebe8925..2b501522f5 100644
--- a/src/widgets/dialogs/qcolordialog_p.h
+++ b/src/widgets/dialogs/qcolordialog_p.h
@@ -63,6 +63,7 @@ class QVBoxLayout;
 class QPushButton;
 class QWellArray;
 class QColorPickingEventFilter;
+class QTimer;
 
 class QColorDialogPrivate : public QDialogPrivate
 {
@@ -75,7 +76,11 @@ public:
         SetColorAll = ShowColor | SelectColor
     };
 
-    QColorDialogPrivate() : options(new QColorDialogOptions) {}
+    QColorDialogPrivate() : options(new QColorDialogOptions)
+#ifdef Q_OS_WIN
+        , updateTimer(0)
+#endif
+    {}
 
     QPlatformColorDialogHelper *platformColorDialogHelper() const
         { return static_cast<QPlatformColorDialogHelper *>(platformHelper()); }
@@ -104,6 +109,8 @@ public:
     void _q_newCustom(int, int);
     void _q_newStandard(int, int);
     void _q_pickScreenColor();
+    void _q_updateColorPicking();
+    void updateColorPicking(const QPoint &pos);
     void releaseColorPicking();
     bool handleColorPickingMouseMove(QMouseEvent *e);
     bool handleColorPickingMouseButtonRelease(QMouseEvent *e);
@@ -136,6 +143,9 @@ public:
 
     QPointer<QObject> receiverToDisconnectOnClose;
     QByteArray memberToDisconnectOnClose;
+#ifdef Q_OS_WIN
+    QTimer *updateTimer;
+#endif
 
 #ifdef Q_WS_MAC
     void openCocoaColorPanel(const QColor &initial,