Implement high-dpi "@2x" image handling.

Make QQuickBaseImage::load() load "@2x" image files
on high-dpi displays. Reload images on screen change
in order to load the correct version depending on
screen dpi. Modify QQuickImageBase::updatePaintNode()
to work with @2x images.

QQuickBaseImage::load() now looks at the target
window's devicePixelRatio and checks for the presence
of a "@2x" file on disk. If found the @2x version
will be used.

Unlike QPixmap, QQuickPixmap has no special knowledge
of "@2x" files. They pixmap system will be asked to
load "@2x" files and will cache them and report the
(device) pixel size, like any other pixmap.

Add auto-test and manual test.

Task-number: QTBUG-32862, QTBUG-33069
Change-Id: I1f57a10075e499f6eee61df5421e1986521c6ab0
Reviewed-by: Andy Nichols <andy.nichols@digia.com>

2 files changed, 44 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickimage/data/heart-highdpi@2x.png b/tests/auto/quick/qquickimage/data/heart-highdpi@2x.png
new file mode 100644
index 0000000000..abe97fee4b
--- /dev/null
+++ b/tests/auto/quick/qquickimage/data/heart-highdpi@2x.png
diff --git a/tests/auto/quick/qquickimage/tst_qquickimage.cpp b/tests/auto/quick/qquickimage/tst_qquickimage.cpp
index b23591b593..0855403d5a 100644
--- a/tests/auto/quick/qquickimage/tst_qquickimage.cpp
+++ b/tests/auto/quick/qquickimage/tst_qquickimage.cpp
@@ -105,6 +105,7 @@ private slots:
     void progressAndStatusChanges();
     void sourceSizeChanges();
     void correctStatus();
+    void highdpi();
 
 private:
     QQmlEngine engine;
@@ -928,6 +929,49 @@ void tst_qquickimage::correctStatus()
     delete obj;
 }
 
+void tst_qquickimage::highdpi()
+{
+    TestHTTPServer server(14449);
+    QVERIFY(server.isValid());
+    server.serveDirectory(dataDirectory());
+
+    QString componentStr = "import QtQuick 2.0\nImage { source: srcImage ;  }";
+    QQmlComponent component(&engine);
+    component.setData(componentStr.toLatin1(), QUrl::fromLocalFile(""));
+    QQmlContext *ctxt = engine.rootContext();
+
+    // Testing "@2x" high-dpi image loading:
+    // The basic case is as follows. Suppose you have foo.png,
+    // which is a 64x64 png that fits in a QML layout. Now,
+    // on a high-dpi system that pixmap would not provide
+    // enough pixels. To fix this the app developer provides
+    // a 128x128 foo@2x.png, which Qt automatically loads.
+    // The image continues to be referred to as "foo.png" in
+    // the QML sources, and reports a size of 64x64.
+    //
+
+    // Load "heart-highdpi@2x.png", which is a 300x300 png. As a 2x scale image it
+    // should render and report a geometry of 150x150.
+    ctxt->setContextProperty("srcImage", testFileUrl("heart-highdpi@2x.png"));
+
+    QQuickImage *obj = qobject_cast<QQuickImage*>(component.create());
+    QVERIFY(obj != 0);
+
+    QCOMPARE(obj->width(), 150.0);
+    QCOMPARE(obj->height(), 150.0);
+    QCOMPARE(obj->paintedWidth(), 150.0);
+    QCOMPARE(obj->paintedHeight(), 150.0);
+
+    // Load a normal 1x image.
+    ctxt->setContextProperty("srcImage", testFileUrl("heart.png"));
+    QCOMPARE(obj->width(), 300.0);
+    QCOMPARE(obj->height(), 300.0);
+    QCOMPARE(obj->paintedWidth(), 300.0);
+    QCOMPARE(obj->paintedHeight(), 300.0);
+
+    delete obj;
+}
+
 QTEST_MAIN(tst_qquickimage)
 
 #include "tst_qquickimage.moc"