Add deviceIndependentSize() to QPixmap and QImage

This function returns the size in device independent
pixels, and should be used when calculating user
interface sizes.


Change-Id: I528123f962595a3da42438ca560289a29aca4917
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/gui/image/qimage.cpp

@@ -1316,7 +1316,7 @@ int QImage::height() const
 
     Returns the size of the image, i.e. its width() and height().
 
-    \sa {QImage#Image Information}{Image Information}
+    \sa {QImage#Image Information}{Image Information}, deviceIndependentSize()
 */
 QSize QImage::size() const
 {
@@ -1449,7 +1449,7 @@ qreal QImage::devicePixelRatio() const
     high-DPI image rather than a large image
     (see \l{Drawing High Resolution Versions of Pixmaps and Images}).
 
-    \sa devicePixelRatio()
+    \sa devicePixelRatio(), deviceIndependentSize()
 */
 void QImage::setDevicePixelRatio(qreal scaleFactor)
 {
@@ -1464,6 +1464,22 @@ void QImage::setDevicePixelRatio(qreal scaleFactor)
         d->devicePixelRatio = scaleFactor;
 }
 
+/*!
+    Returns the size of the pixmap in device independent pixels.
+
+    This value should be used when using the pixmap size in user interface
+    size calculations.
+
+    The return value is equivalent to pixmap.size() / pixmap.devicePixelRatio(),
+*/
+QSizeF QImage::deviceIndependentSize() const
+{
+    if (!d)
+        return QSizeF(0, 0);
+    return QSizeF(d->width, d->height) / d->devicePixelRatio;
+}
+
+
 /*!
     \since 5.10
     Returns the image data size in bytes.

src/gui/image/qimage.h

@@ -219,6 +219,7 @@ public:
 
     qreal devicePixelRatio() const;
     void setDevicePixelRatio(qreal scaleFactor);
+    QSizeF deviceIndependentSize() const;
 
     void fill(uint pixel);
     void fill(const QColor &color);

src/gui/image/qpixmap.cpp

@@ -633,7 +633,7 @@ qreal QPixmap::devicePixelRatio() const
     high-DPI pixmap rather than a large pixmap
     (see \l{Drawing High Resolution Versions of Pixmaps and Images}).
 
-    \sa devicePixelRatio()
+    \sa devicePixelRatio(), devicePixelSize()
 */
 void QPixmap::setDevicePixelRatio(qreal scaleFactor)
 {
@@ -647,6 +647,21 @@ void QPixmap::setDevicePixelRatio(qreal scaleFactor)
     data->setDevicePixelRatio(scaleFactor);
 }
 
+/*!
+    Returns the size of the pixmap in device independent pixels.
+
+    This value should be used when using the pixmap size in user interface
+    size calculations.
+
+    The return value is equivalent to pixmap.size() / pixmap.devicePixelRatio(),
+*/
+QSizeF QPixmap::deviceIndependentSize() const
+{
+    if (!data)
+        return QSizeF(0, 0);
+    return QSizeF(data->width(), data->height()) / data->devicePixelRatio();
+}
+
 #ifndef QT_NO_IMAGE_HEURISTIC_MASK
 /*!
     Creates and returns a heuristic mask for this pixmap.

src/gui/image/qpixmap.h

@@ -101,6 +101,7 @@ public:
 
     qreal devicePixelRatio() const;
     void setDevicePixelRatio(qreal scaleFactor);
+    QSizeF deviceIndependentSize() const;
 
     bool hasAlpha() const;
     bool hasAlphaChannel() const;

tests/auto/gui/image/qimage/tst_qimage.cpp

@@ -212,6 +212,7 @@ private slots:
     void cleanupFunctions();
 
     void devicePixelRatio();
+    void deviceIndependentSize();
     void rgb30Unpremul();
     void rgb30Repremul_data();
     void rgb30Repremul();
@@ -3473,6 +3474,15 @@ void tst_QImage::devicePixelRatio()
     QCOMPARE(b.devicePixelRatio(), qreal(1.0));
 }
 
+void tst_QImage::deviceIndependentSize() {
+    QImage a(64, 64, QImage::Format_ARGB32);
+    a.fill(Qt::white);
+    a.setDevicePixelRatio(1.0);
+    QCOMPARE(a.deviceIndependentSize(), QSizeF(64, 64));
+    a.setDevicePixelRatio(2.0);
+    QCOMPARE(a.deviceIndependentSize(), QSizeF(32, 32));
+}
+
 void tst_QImage::rgb30Unpremul()
 {
     QImage a(3, 1, QImage::Format_A2RGB30_Premultiplied);

tests/auto/gui/image/qpixmap/tst_qpixmap.cpp

@@ -161,6 +161,7 @@ private slots:
 
     void copyOnNonAlignedBoundary();
     void devicePixelRatio();
+    void deviceIndependentSize();
 
 private:
     const QString m_prefix;
@@ -1678,5 +1679,14 @@ void tst_QPixmap::devicePixelRatio()
     QCOMPARE(b.devicePixelRatio(), qreal(1.0));
 }
 
+void tst_QPixmap::deviceIndependentSize() {
+    QPixmap a(64, 64);
+    a.fill(Qt::white);
+    a.setDevicePixelRatio(1.0);
+    QCOMPARE(a.deviceIndependentSize(), QSizeF(64, 64));
+    a.setDevicePixelRatio(2.0);
+    QCOMPARE(a.deviceIndependentSize(), QSizeF(32, 32));
+}
+
 QTEST_MAIN(tst_QPixmap)
 #include "tst_qpixmap.moc"