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: I206e050b6241f8935b4404c7a28b024a9e00d46c
Task-id: QTBUG-38485
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

2 files changed, 5 insertions, 3 deletions

diff --git a/src/gui/image/qicon.cpp b/src/gui/image/qicon.cpp
index 8172ecbb48..681e7e3f79 100644
--- a/src/gui/image/qicon.cpp
+++ b/src/gui/image/qicon.cpp
@@ -1026,7 +1026,8 @@ void QIcon::addFile(const QString &fileName, const QSize &size, Mode mode, State
     d->engine->addFile(fileName, size, mode, state);
 
     // Check if a "@2x" file exists and add it.
-    if (qApp->devicePixelRatio() > 1.0) {
+    static bool disable2xImageLoading = !qgetenv("QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING").isEmpty();
+    if (!disable2xImageLoading && qApp->devicePixelRatio() > 1.0) {
         int dotIndex = fileName.lastIndexOf(QLatin1Char('.'));
         if (dotIndex != -1) {
             QString at2xfileName = fileName;
diff --git a/src/gui/image/qimagereader.cpp b/src/gui/image/qimagereader.cpp
index 091837b8b4..a10198a006 100644
--- a/src/gui/image/qimagereader.cpp
+++ b/src/gui/image/qimagereader.cpp
@@ -1247,8 +1247,9 @@ bool QImageReader::read(QImage *image)
     }
 
     // successful read; check for "@2x" file name suffix and set device pixel ratio.
-    if (QFileInfo(fileName()).baseName().endsWith(QLatin1String("@2x"))) {
-        image->setDevicePixelRatio(2.0);
+    static bool disable2xImageLoading = !qgetenv("QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING").isEmpty();
+    if (!disable2xImageLoading && QFileInfo(fileName()).baseName().endsWith(QLatin1String("@2x"))) {
+           image->setDevicePixelRatio(2.0);
     }
 
     return true;