Deprecate implicit QPixmap conversion to QBitmap

It is lossy, so should be requested explicitly, using a dedicated
fromPixmap factory function.

Deprecate the constructor and assignment operator, and make the
constructor explicit.

[ChangeLog][QtGui][QBitmap] Implicitly constructing and assigning
to a QBitmap from a QPixmap has been deprecated, and the respective
constructor has been made explicit. Use the fromPixmap factory
function instead.

Change-Id: I68ce85b26c901415137b664a1db687021d48bae0
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

7 files changed, 76 insertions, 48 deletions

diff --git a/examples/widgets/mainwindows/mainwindow/colorswatch.cpp b/examples/widgets/mainwindows/mainwindow/colorswatch.cpp
index 77e59d764e..cb568a7a5a 100644
--- a/examples/widgets/mainwindows/mainwindow/colorswatch.cpp
+++ b/examples/widgets/mainwindows/mainwindow/colorswatch.cpp
@@ -680,7 +680,7 @@ void BlueTitleBar::updateMask()
     Q_ASSERT(dw);
 
     QRect rect = dw->rect();
-    QPixmap bitmap(dw->size());
+    QBitmap bitmap(dw->size());
 
     {
         QPainter painter(&bitmap);
diff --git a/src/gui/image/qbitmap.cpp b/src/gui/image/qbitmap.cpp
index 58953e8d9a..0505717fb3 100644
--- a/src/gui/image/qbitmap.cpp
+++ b/src/gui/image/qbitmap.cpp
@@ -139,20 +139,6 @@ QBitmap::QBitmap(const QSize &size)
 */
 
 /*!
-    Constructs a bitmap that is a copy of the given \a pixmap.
-
-    If the pixmap has a depth greater than 1, the resulting bitmap
-    will be dithered automatically.
-
-    \sa QPixmap::depth(), fromImage(), fromData()
-*/
-
-QBitmap::QBitmap(const QPixmap &pixmap)
-{
-    QBitmap::operator=(pixmap);
-}
-
-/*!
     Constructs a bitmap from the file specified by the given \a
     fileName. If the file does not exist, or has an unknown format,
     the bitmap becomes a null bitmap.
@@ -171,30 +157,6 @@ QBitmap::QBitmap(const QString& fileName, const char *format)
 }
 
 /*!
-    \overload
-
-    Assigns the given \a pixmap to this bitmap and returns a reference
-    to this bitmap.
-
-    If the pixmap has a depth greater than 1, the resulting bitmap
-    will be dithered automatically.
-
-    \sa QPixmap::depth()
- */
-
-QBitmap &QBitmap::operator=(const QPixmap &pixmap)
-{
-    if (pixmap.isNull()) {                        // a null pixmap
-        QBitmap(0, 0).swap(*this);
-    } else if (pixmap.depth() == 1) {                // 1-bit pixmap
-        QPixmap::operator=(pixmap);                // shallow assignment
-    } else {                                        // n-bit depth pixmap
-        *this = fromImage(pixmap.toImage());        // will dither image
-    }
-    return *this;
-}
-
-/*!
     \fn void QBitmap::swap(QBitmap &other)
     \since 4.8
 
@@ -225,7 +187,7 @@ static QBitmap makeBitmap(QImage &&image, Qt::ImageConversionFlags flags)
     QScopedPointer<QPlatformPixmap> data(QGuiApplicationPrivate::platformIntegration()->createPlatformPixmap(QPlatformPixmap::BitmapType));
 
     data->fromImageInPlace(image, flags | Qt::MonoOnly);
-    return QPixmap(data.take());
+    return QBitmap::fromPixmap(QPixmap(data.take()));
 }
 
 /*!
@@ -288,6 +250,68 @@ QBitmap QBitmap::fromData(const QSize &size, const uchar *bits, QImage::Format m
 }
 
 /*!
+    Returns a copy of the given \a pixmap converted to a bitmap.
+
+    If the pixmap has a depth greater than 1, the resulting bitmap
+    will be dithered automatically.
+
+    \sa QPixmap::depth()
+*/
+
+QBitmap QBitmap::fromPixmap(const QPixmap &pixmap)
+{
+    if (pixmap.isNull()) {                        // a null pixmap
+        return QBitmap(0, 0);
+    } else if (pixmap.depth() == 1) {             // 1-bit pixmap
+        QBitmap bm;
+        if (pixmap.paintingActive()) {            // make a deep copy
+            pixmap.copy().swap(bm);
+        } else {
+            bm.data = pixmap.data;                // shallow assignment
+        }
+        return bm;
+    }
+    // n-bit depth pixmap, will dither image
+    return fromImage(pixmap.toImage());
+}
+
+#if QT_DEPRECATED_SINCE(6, 0)
+/*!
+    \obsolete Use fromPixmap instead.
+    Constructs a bitmap that is a copy of the given \a pixmap.
+
+    If the pixmap has a depth greater than 1, the resulting bitmap
+    will be dithered automatically.
+
+    \sa QPixmap::depth(), fromImage(), fromData()
+*/
+
+QBitmap::QBitmap(const QPixmap &pixmap)
+{
+    *this = QBitmap::fromPixmap(pixmap);
+}
+
+/*!
+    \obsolete Use fromPixmap instead.
+    \overload
+
+    Assigns the given \a pixmap to this bitmap and returns a reference
+    to this bitmap.
+
+    If the pixmap has a depth greater than 1, the resulting bitmap
+    will be dithered automatically.
+
+    \sa QPixmap::depth()
+ */
+
+QBitmap &QBitmap::operator=(const QPixmap &pixmap)
+{
+    *this = QBitmap::fromPixmap(pixmap);
+    return *this;
+}
+#endif
+
+/*!
     Returns a copy of this bitmap, transformed according to the given
     \a matrix.
 
@@ -295,8 +319,7 @@ QBitmap QBitmap::fromData(const QSize &size, const uchar *bits, QImage::Format m
  */
 QBitmap QBitmap::transformed(const QTransform &matrix) const
 {
-    QBitmap bm = QPixmap::transformed(matrix);
-    return bm;
+    return QBitmap::fromPixmap(QPixmap::transformed(matrix));
 }
 
 QT_END_NAMESPACE
diff --git a/src/gui/image/qbitmap.h b/src/gui/image/qbitmap.h
index a114db17e0..9052e62db6 100644
--- a/src/gui/image/qbitmap.h
+++ b/src/gui/image/qbitmap.h
@@ -52,12 +52,16 @@ class Q_GUI_EXPORT QBitmap : public QPixmap
 {
 public:
     QBitmap();
-    QBitmap(const QPixmap &);
+#if QT_DEPRECATED_SINCE(6, 0)
+    QT_DEPRECATED_VERSION_X_6_0("Use fromPixmap instead.") explicit QBitmap(const QPixmap &);
+#endif
     QBitmap(int w, int h);
     explicit QBitmap(const QSize &);
     explicit QBitmap(const QString &fileName, const char *format = nullptr);
 
-    QBitmap &operator=(const QPixmap &);
+#if QT_DEPRECATED_SINCE(6, 0)
+    QT_DEPRECATED_VERSION_X_6_0("Use fromPixmap instead.") QBitmap &operator=(const QPixmap &);
+#endif
     inline void swap(QBitmap &other) { QPixmap::swap(other); } // prevent QBitmap<->QPixmap swaps
     operator QVariant() const;
 
@@ -67,6 +71,7 @@ public:
     static QBitmap fromImage(QImage &&image, Qt::ImageConversionFlags flags = Qt::AutoColor);
     static QBitmap fromData(const QSize &size, const uchar *bits,
                             QImage::Format monoFormat = QImage::Format_MonoLSB);
+    static QBitmap fromPixmap(const QPixmap &pixmap);
 
     QBitmap transformed(const QTransform &matrix) const;
 
diff --git a/src/gui/kernel/qguivariant.cpp b/src/gui/kernel/qguivariant.cpp
index 1af0692173..d7e88025b9 100644
--- a/src/gui/kernel/qguivariant.cpp
+++ b/src/gui/kernel/qguivariant.cpp
@@ -155,7 +155,7 @@ static const struct : QMetaTypeModuleHelper
         QMETATYPE_CONVERTER(QPixmap, QImage, result = QPixmap::fromImage(source); return true;);
         QMETATYPE_CONVERTER(QImage, QPixmap, result = source.toImage(); return true;);
         QMETATYPE_CONVERTER(QPixmap, QBitmap, result = source; return true;);
-        QMETATYPE_CONVERTER(QBitmap, QPixmap, result = source; return true;);
+        QMETATYPE_CONVERTER(QBitmap, QPixmap, result = QBitmap::fromPixmap(source); return true;);
         QMETATYPE_CONVERTER(QImage, QBitmap, result = source.toImage(); return true;);
         QMETATYPE_CONVERTER(QBitmap, QImage, result = QBitmap::fromImage(source); return true;);
         QMETATYPE_CONVERTER(QPixmap, QBrush, result = source.texture(); return true;);
diff --git a/src/gui/kernel/qshapedpixmapdndwindow.cpp b/src/gui/kernel/qshapedpixmapdndwindow.cpp
index 1a85a5e853..e58d37693a 100644
--- a/src/gui/kernel/qshapedpixmapdndwindow.cpp
+++ b/src/gui/kernel/qshapedpixmapdndwindow.cpp
@@ -76,7 +76,7 @@ void QShapedPixmapWindow::setPixmap(const QPixmap &pixmap)
                 const auto pixmapDpr = m_pixmap.devicePixelRatio();
                 const auto winDpr = devicePixelRatio();
                 const auto maskSize = (QSizeF(m_pixmap.size()) * winDpr / pixmapDpr).toSize();
-                platformWindow->setMask(QBitmap(mask.scaled(maskSize)));
+                platformWindow->setMask(QBitmap::fromPixmap(mask.scaled(maskSize)));
             }
         }
     }
diff --git a/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp b/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
index c992b487bc..f262996980 100644
--- a/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
+++ b/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
@@ -1176,7 +1176,7 @@ static QCursor qCursorData(int index)
     case 3: return QCursor(Qt::BlankCursor);
     case 4: return QCursor(Qt::BlankCursor);
     case 5: return QCursor(QPixmap(open_xpm), 1, 1);
-    case 6: { QPixmap pm(open_xpm); return QCursor(QBitmap(pm), pm.mask(), 3, 4); }
+    case 6: { QPixmap pm(open_xpm); return QCursor(QBitmap::fromPixmap(pm), pm.mask(), 3, 4); }
     case 7: return QCursor(QPixmap(open_xpm), -1, 5);
     case 8: return QCursor(QPixmap(open_xpm), 5, -1);
     }
diff --git a/tests/auto/gui/painting/qregion/tst_qregion.cpp b/tests/auto/gui/painting/qregion/tst_qregion.cpp
index dc694e1107..27327d8d1a 100644
--- a/tests/auto/gui/painting/qregion/tst_qregion.cpp
+++ b/tests/auto/gui/painting/qregion/tst_qregion.cpp
@@ -382,7 +382,7 @@ void tst_QRegion::bitmapRegion()
         QVERIFY(region.isEmpty());
     }
     {
-        circle = QPixmap(circle_xpm);
+        circle = QBitmap::fromPixmap(QPixmap(circle_xpm));
         QRegion region(circle);
 
         //// These should not be inside the circe