Add opt-out environment variable for @2x images

There are cases where @2x images are in use but
where you don't want the associated behavior:
- You are implementing an image editor
- You are inheriting a resource set which has @2x
  images, but don't want that behavior with Qt.

Add support for disabling @2x behavior with QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING.

Change-Id: Ia570dfe556e0571a19e5ebdc626c4a7e626721b9
Task-id: QTBUG-38485
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/quick/items/qquickimagebase.cpp b/src/quick/items/qquickimagebase.cpp
index 66a56cc8bf..bf67cbef26 100644
--- a/src/quick/items/qquickimagebase.cpp
+++ b/src/quick/items/qquickimagebase.cpp
@@ -332,6 +332,11 @@ void QQuickImageBase::resolve2xLocalFile(const QUrl &url, qreal targetDevicePixe
     Q_ASSERT(sourceUrl);
     Q_ASSERT(sourceDevicePixelRatio);
 
+    // Bail out if "@2x" image loading is disabled, don't change the source url or devicePixelRatio.
+    static bool disable2xImageLoading = !qgetenv("QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING").isEmpty();
+    if (disable2xImageLoading)
+        return;
+
     QString localFile = QQmlFile::urlToLocalFileOrQrc(url);
 
     // Non-local file path: @2x loading is not supported.