Add a screen color picker button to QColorDialog

Add a new button with which any color present on the screen can be picked
up. This feature is very useful in any image processing application.

Notice:
--I have setMouseTracking to true because I consider that it makes much
easier to grab the desired color.
--I have set the cursor manually because for some unknown reason the
cursor wouldn't change with grabMouse(Qt::CrossCursor).

Task-number: QTBUG-14332

Change-Id: I39e3543d3ed55276f43d569a2f03087bbf89b27a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Kevin Ottens <kevin.ottens@kdab.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/widgets/dialogs/qcolordialog.cpp

@@ -63,6 +63,8 @@
 #include "qmimedata.h"
 #include "qspinbox.h"
 #include "qdialogbuttonbox.h"
+#include "qscreen.h"
+#include "qcursor.h"
 
 QT_BEGIN_NAMESPACE
 
@@ -1417,6 +1419,15 @@ bool QColorDialogPrivate::selectColor(const QColor &col)
     return false;
 }
 
+QColor QColorDialogPrivate::grabScreenColor(const QPoint &p)
+{
+    const QDesktopWidget *desktop = QApplication::desktop();
+    const QPixmap pixmap = QGuiApplication::screens().at(desktop->screenNumber())->grabWindow(desktop->winId(),
+                                                                                              p.x(), p.y(), 1, 1);
+    QImage i = pixmap.toImage();
+    return i.pixel(0, 0);
+}
+
 //sets all widgets except cs to display rgb
 void QColorDialogPrivate::_q_newColorTypedIn(QRgb rgb)
 {
@@ -1442,6 +1453,48 @@ void QColorDialogPrivate::_q_newStandard(int r, int c)
         custom->setSelected(-1,-1);
 }
 
+void QColorDialogPrivate::_q_pickScreenColor()
+{
+    Q_Q(QColorDialog);
+    screenColorPicking = true;
+    // If user pushes Escape, the last color before picking will be restored.
+    beforeScreenColorPicking = cs->currentColor();
+    /*For some reason, q->grabMouse(Qt::CrossCursor) doesn't change
+     * the cursor, and therefore I have to change it manually.
+     */
+    q->grabMouse();
+    q->setCursor(Qt::CrossCursor);
+    q->grabKeyboard();
+    /* With setMouseTracking(true) the desired color can be more precisedly picked up,
+     * and continuously pushing the mouse button is not necessary.
+     */
+    q->setMouseTracking(true);
+
+    addCusBt->setDisabled(true);
+    buttons->setDisabled(true);
+    screenColorPickerButton->setDisabled(true);
+
+    q->setCurrentColor(grabScreenColor(QCursor::pos()));
+    lblScreenColorInfo->setText(QColorDialog::tr("Cursor at %1, %2, color: %3\nPress ESC to cancel")
+                                .arg(QCursor::pos().x())
+                                .arg(QCursor::pos().y())
+                                .arg(q->currentColor().name()));
+}
+
+void QColorDialogPrivate::releaseColorPicking()
+{
+    Q_Q(QColorDialog);
+    screenColorPicking = false;
+    q->releaseMouse();
+    q->releaseKeyboard();
+    q->setCursor(Qt::ArrowCursor);
+    q->setMouseTracking(false);
+    lblScreenColorInfo->setText(QLatin1String("\n"));
+    addCusBt->setDisabled(false);
+    buttons->setDisabled(false);
+    screenColorPickerButton->setDisabled(false);
+}
+
 void QColorDialogPrivate::init(const QColor &initial)
 {
     Q_Q(QColorDialog);
@@ -1450,7 +1503,7 @@ void QColorDialogPrivate::init(const QColor &initial)
     q->setWindowTitle(QColorDialog::tr("Select Color"));
 
     nativeDialogInUse = (platformColorDialogHelper() != 0);
-
+    screenColorPicking = false;
     nextCust = 0;
     QVBoxLayout *mainLay = new QVBoxLayout(q);
     // there's nothing in this dialog that benefits from sizing up
@@ -1486,6 +1539,15 @@ void QColorDialogPrivate::init(const QColor &initial)
         leftLay->addWidget(lblBasicColors);
         leftLay->addWidget(standard);
 
+#if !defined(Q_OS_WINCE) && !defined(QT_SMALL_COLORDIALOG)
+        // The screen color picker button
+        screenColorPickerButton = new QPushButton(QColorDialog::tr("Pick Screen Color"));
+        leftLay->addWidget(screenColorPickerButton);
+        lblScreenColorInfo = new QLabel(QLatin1String("\n"));
+        leftLay->addWidget(lblScreenColorInfo);
+        q->connect(screenColorPickerButton, SIGNAL(clicked()), SLOT(_q_pickScreenColor()));
+#endif
+
 #if !defined(Q_OS_WINCE)
         leftLay->addStretch();
 #endif
@@ -1658,6 +1720,11 @@ static const Qt::WindowFlags DefaultWindowFlags =
     during the execution of the program. Use setCustomColor() to set
     the custom colors, and use customColor() to get them.
 
+    When pressing the "Pick Screen Color" button, the cursor changes to a haircross
+    and the colors on the screen are scanned. The user can pick up one by clicking
+    the mouse or the Enter button. Pressing Escape restores the last color selected
+    before entering this mode.
+
     The \l{dialogs/standarddialogs}{Standard Dialogs} example shows
     how to use QColorDialog as well as other built-in Qt dialogs.
 
@@ -1971,6 +2038,57 @@ void QColorDialog::changeEvent(QEvent *e)
     QDialog::changeEvent(e);
 }
 
+/*!
+    \reimp
+*/
+void QColorDialog::mouseMoveEvent(QMouseEvent *e)
+{
+    Q_D(QColorDialog);
+    if (d->screenColorPicking) {
+        setCurrentColor(d->grabScreenColor(e->globalPos()));
+        d->lblScreenColorInfo->setText(QColorDialog::tr("Cursor at %1, %2, color: %3\nPress ESC to cancel")
+                                       .arg(e->globalPos().x())
+                                       .arg(e->globalPos().y())
+                                       .arg(currentColor().name()));
+        return;
+    }
+    QDialog::mouseMoveEvent(e);
+}
+
+/*!
+    \reimp
+*/
+void QColorDialog::mouseReleaseEvent(QMouseEvent *e)
+{
+    Q_D(QColorDialog);
+    if (d->screenColorPicking) {
+        setCurrentColor(d->grabScreenColor(e->globalPos()));
+        d->releaseColorPicking();
+        return;
+    }
+    QDialog::mouseReleaseEvent(e);
+}
+
+/*!
+    \reimp
+*/
+void QColorDialog::keyPressEvent(QKeyEvent *e)
+{
+    Q_D(QColorDialog);
+    if (d->screenColorPicking) {
+        if (e->key() == Qt::Key_Escape) {
+            d->releaseColorPicking();
+            d->setCurrentColor(d->beforeScreenColorPicking);
+        } else if (e->key() == Qt::Key_Return || e->key() == Qt::Key_Enter) {
+            setCurrentColor(d->grabScreenColor(QCursor::pos()));
+            d->releaseColorPicking();
+        }
+        e->accept();
+        return;
+    }
+    QDialog::keyPressEvent(e);
+}
+
 /*!
   Closes the dialog and sets its result code to \a result. If this dialog
   is shown with exec(), done() causes the local event loop to finish,

src/widgets/dialogs/qcolordialog.h

@@ -112,6 +112,9 @@ Q_SIGNALS:
 
 protected:
     void changeEvent(QEvent *event);
+    virtual void mouseMoveEvent(QMouseEvent *);
+    virtual void mouseReleaseEvent(QMouseEvent *);
+    virtual void keyPressEvent(QKeyEvent *);
     void done(int result);
 
 private:
@@ -122,6 +125,7 @@ private:
     Q_PRIVATE_SLOT(d_func(), void _q_newColorTypedIn(QRgb rgb))
     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())
     friend class QColorShower;
 };
 

src/widgets/dialogs/qcolordialog_p.h

@@ -87,6 +87,7 @@ public:
     void setCurrentColor(QRgb rgb);
     void setCurrentQColor(const QColor &color);
     bool selectColor(const QColor &color);
+    QColor grabScreenColor(const QPoint &p);
 
     int currentAlpha() const;
     void setCurrentAlpha(int a);
@@ -100,6 +101,8 @@ public:
     void _q_newColorTypedIn(QRgb rgb);
     void _q_newCustom(int, int);
     void _q_newStandard(int, int);
+    void _q_pickScreenColor();
+    void releaseColorPicking();
 
     QWellArray *custom;
     QWellArray *standard;
@@ -111,12 +114,16 @@ public:
     QColorShower *cs;
     QLabel *lblBasicColors;
     QLabel *lblCustomColors;
+    QLabel *lblScreenColorInfo;
     QPushButton *ok;
     QPushButton *cancel;
     QPushButton *addCusBt;
+    QPushButton *screenColorPickerButton;
     QColor selectedQColor;
     int nextCust;
     bool smallDisplay;
+    bool screenColorPicking;
+    QRgb beforeScreenColorPicking;
     QSharedPointer<QColorDialogOptions> options;
 
     QPointer<QObject> receiverToDisconnectOnClose;