Preserve aspect ratio when setting Image.sourceSize

Setting both sourceSize.width and sourceSize.height results in changing
the image aspect ratio.  This is never what you'd want.

Fit the image to the provided sourceSize, maintaining the aspect ratio.

Task-number: QTBUG-21161
Change-Id: I77e9aacb8d31475d5df0aef1de52c0edbd1e2fc9
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>

doc/src/declarative/whatsnew.qdoc

@@ -107,6 +107,7 @@ Added topMargin, bottomMargin, leftMargin, rightMargin, xOrigin, yOrigin propert
 
 Image has two new properties: horizontalAlignment and verticalAlignment. It also has a new value for
 fillMode (Image.Pad) that does not transform the image.
+Setting Image sourceSize.width and sourceSize.height will now fit the image to the size, maintaining aspect.
 
 Grid now has rowSpacing and columnSpacing properties.
 

src/quick/items/qquickimage.cpp

@@ -404,6 +404,10 @@ qreal QQuickImage::paintedHeight() const
     other dimension is set in proportion to preserve the source image's aspect ratio.
     (The \l fillMode is independent of this.)
 
+    If both the sourceSize.width and sourceSize.height are set the image will be scaled
+    down to fit within the specified size, maintaining the image's aspect ratio.  The actual
+    size of the image after scaling is available via \l implicitWidth and \l implicitHeight.
+
     If the source is an intrinsically scalable image (eg. SVG), this property
     determines the size of the loaded image regardless of intrinsic size.
     Avoid changing this property dynamically; rendering an SVG is \e slow compared
@@ -413,7 +417,7 @@ qreal QQuickImage::paintedHeight() const
     be no greater than this property specifies. For some formats (currently only JPEG),
     the whole image will never actually be loaded into memory.
 
-    Since QtQuick 1.1 the sourceSize can be cleared to the natural size of the image
+    sourceSize can be cleared to the natural size of the image
     by setting sourceSize to \c undefined.
 
     \note \e {Changing this property dynamically causes the image source to be reloaded,

src/quick/util/qdeclarativepixmapcache.cpp

@@ -323,20 +323,22 @@ static bool readImage(const QUrl& url, QIODevice *dev, QImage *image, QString *e
         force_scale = true;
     }
 
-    bool scaled = false;
     if (requestSize.width() > 0 || requestSize.height() > 0) {
         QSize s = imgio.size();
+        qreal ratio = 0.0;
         if (requestSize.width() && (force_scale || requestSize.width() < s.width())) {
-            if (requestSize.height() <= 0)
-                s.setHeight(s.height()*requestSize.width()/s.width());
-            s.setWidth(requestSize.width()); scaled = true;
+            ratio = qreal(requestSize.width())/s.width();
         }
         if (requestSize.height() && (force_scale || requestSize.height() < s.height())) {
-            if (requestSize.width() <= 0)
-                s.setWidth(s.width()*requestSize.height()/s.height());
-            s.setHeight(requestSize.height()); scaled = true;
+            qreal hr = qreal(requestSize.height())/s.height();
+            if (ratio == 0.0 || hr < ratio)
+                ratio = hr;
+        }
+        if (ratio > 0.0) {
+            s.setHeight(qRound(s.height() * ratio));
+            s.setWidth(qRound(s.width() * ratio));
+            imgio.setScaledSize(s);
         }
-        if (scaled) { imgio.setScaledSize(s); }
     }
 
     if (impsize)

tests/auto/qtquick2/qquickimage/data/sourceSize.qml

@@ -0,0 +1,7 @@
+import QtQuick 2.0
+
+Image {
+    source: "heart.png"
+    sourceSize.width: srcWidth
+    sourceSize.height: srcHeight
+}

tests/auto/qtquick2/qquickimage/tst_qquickimage.cpp

@@ -95,6 +95,8 @@ private slots:
     void sourceSize_QTBUG_16389();
     void nullPixmapPaint();
     void imageCrash_QTBUG_22125();
+    void sourceSize_data();
+    void sourceSize();
 
 private:
     QDeclarativeEngine engine;
@@ -498,6 +500,8 @@ void tst_qquickimage::tiling_QTBUG_6716()
             QVERIFY(img.pixel(x, y) == qRgb(0, 255, 0));
         }
     }
+
+    delete canvas;
 }
 
 void tst_qquickimage::tiling_QTBUG_6716_data()
@@ -674,6 +678,8 @@ void tst_qquickimage::nullPixmapPaint()
     qInstallMsgHandler(previousMsgHandler);
     QVERIFY(numberOfWarnings == 0);
     delete image;
+
+    delete canvas;
 }
 
 void tst_qquickimage::imageCrash_QTBUG_22125()
@@ -698,6 +704,46 @@ void tst_qquickimage::imageCrash_QTBUG_22125()
     QCoreApplication::processEvents();
 }
 
+void tst_qquickimage::sourceSize_data()
+{
+    QTest::addColumn<int>("sourceWidth");
+    QTest::addColumn<int>("sourceHeight");
+    QTest::addColumn<qreal>("implicitWidth");
+    QTest::addColumn<qreal>("implicitHeight");
+
+    QTest::newRow("unscaled") << 0 << 0 << 300.0 << 300.0;
+    QTest::newRow("scale width") << 100 << 0 << 100.0 << 100.0;
+    QTest::newRow("scale height") << 0 << 150 << 150.0 << 150.0;
+    QTest::newRow("larger sourceSize") << 400 << 400 << 300.0 << 300.0;
+}
+
+void tst_qquickimage::sourceSize()
+{
+    QFETCH(int, sourceWidth);
+    QFETCH(int, sourceHeight);
+    QFETCH(qreal, implicitWidth);
+    QFETCH(qreal, implicitHeight);
+
+    QQuickView *canvas = new QQuickView(0);
+    QDeclarativeContext *ctxt = canvas->rootContext();
+    ctxt->setContextProperty("srcWidth", sourceWidth);
+    ctxt->setContextProperty("srcHeight", sourceHeight);
+
+    canvas->setSource(testFileUrl("sourceSize.qml"));
+    canvas->show();
+    qApp->processEvents();
+
+    QQuickImage *image = qobject_cast<QQuickImage*>(canvas->rootObject());
+    QVERIFY(image);
+
+    QCOMPARE(image->sourceSize().width(), sourceWidth);
+    QCOMPARE(image->sourceSize().height(), sourceHeight);
+    QCOMPARE(image->implicitWidth(), implicitWidth);
+    QCOMPARE(image->implicitHeight(), implicitHeight);
+
+    delete canvas;
+}
+
 QTEST_MAIN(tst_qquickimage)
 
 #include "tst_qquickimage.moc"