QmlDesigner: Return placeholder preview image for non-visual components

Preview image is returned when a 2D item render results in a blank
image.

Also improved device pixel ratio handling. No longer always render
preview at 2x ratio, if not needed.

Change-Id: I67b7563dffea523ea85be23b6a0e8b802c0f03fb
Fixes: QDS-2893
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

4 files changed, 31 insertions, 2 deletions

diff --git a/share/qtcreator/qml/qmlpuppet/images/non-visual-component.png b/share/qtcreator/qml/qmlpuppet/images/non-visual-component.png
new file mode 100644
index 0000000000..f66e2b8b11
--- /dev/null
+++ b/share/qtcreator/qml/qmlpuppet/images/non-visual-component.png
diff --git a/share/qtcreator/qml/qmlpuppet/images/non-visual-component@2x.png b/share/qtcreator/qml/qmlpuppet/images/non-visual-component@2x.png
new file mode 100644
index 0000000000..25a136ff25
--- /dev/null
+++ b/share/qtcreator/qml/qmlpuppet/images/non-visual-component@2x.png
diff --git a/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5informationnodeinstanceserver.cpp b/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5informationnodeinstanceserver.cpp
index 2963119def..ecd066d16c 100644
--- a/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5informationnodeinstanceserver.cpp
+++ b/share/qtcreator/qml/qmlpuppet/qml2puppet/instances/qt5informationnodeinstanceserver.cpp
@@ -101,6 +101,30 @@ static QVariant objectToVariant(QObject *object)
     return QVariant::fromValue(object);
 }
 
+static QImage nonVisualComponentPreviewImage()
+{
+    static double ratio = qgetenv("FORMEDITOR_DEVICE_PIXEL_RATIO").toDouble();
+    if (ratio == 1.) {
+        static const QImage image(":/qtquickplugin/images/non-visual-component.png");
+        return image;
+    } else {
+        static const QImage image(":/qtquickplugin/images/non-visual-component@2x.png");
+        return image;
+    }
+}
+
+static bool imageHasContent(const QImage &image)
+{
+    // Check if any image pixel contains non-zero data
+    const uchar *pData = image.constBits();
+    const qsizetype size = image.sizeInBytes();
+    for (qsizetype i = 0; i < size; ++i) {
+        if (*(pData++) != 0)
+            return true;
+    }
+    return false;
+}
+
 QQuickView *Qt5InformationNodeInstanceServer::createAuxiliaryQuickView(const QUrl &url,
                                                                        QQuickItem *&rootItem)
 {
@@ -556,7 +580,7 @@ void Qt5InformationNodeInstanceServer::doRenderModelNode3DImageView()
                 ServerNodeInstance instance = instanceForId(m_modelNodePreviewImageCommand.instanceId());
                 instanceObj = instance.internalObject();
             }
-            QSize renderSize = m_modelNodePreviewImageCommand.size() * 2;
+            QSize renderSize = m_modelNodePreviewImageCommand.size();
 
             QMetaObject::invokeMethod(m_ModelNode3DImageViewRootItem, "createViewForObject",
                                       Q_ARG(QVariant, objectToVariant(instanceObj)),
@@ -652,7 +676,7 @@ void Qt5InformationNodeInstanceServer::doRenderModelNode2DImageView()
             // Some component may expect to always be shown at certain size, so their layouts may
             // not support scaling, so let's always render at the default size if item has one and
             // scale the resulting image instead.
-            QSize finalSize = m_modelNodePreviewImageCommand.size() * 2;
+            QSize finalSize = m_modelNodePreviewImageCommand.size();
             QRectF renderRect = itemBoundingRect(instanceItem);
             QSize renderSize = renderRect.size().toSize();
             if (renderSize.isEmpty()) {
@@ -665,6 +689,9 @@ void Qt5InformationNodeInstanceServer::doRenderModelNode2DImageView()
 
             renderImage = designerSupport()->renderImageForItem(m_ModelNode2DImageViewContentItem, renderRect, renderSize);
 
+            if (!imageHasContent(renderImage))
+                renderImage = nonVisualComponentPreviewImage();
+
             if (renderSize != finalSize)
                 renderImage = renderImage.scaled(finalSize, Qt::KeepAspectRatio);
 
diff --git a/share/qtcreator/qml/qmlpuppet/qmlpuppet.qrc b/share/qtcreator/qml/qmlpuppet/qmlpuppet.qrc
index d5a50ed566..e094303014 100644
--- a/share/qtcreator/qml/qmlpuppet/qmlpuppet.qrc
+++ b/share/qtcreator/qml/qmlpuppet/qmlpuppet.qrc
@@ -3,6 +3,8 @@
         <file>images/template_image.png</file>
         <file>html/welcome.html</file>
         <file>images/webkit.png</file>
+        <file>images/non-visual-component.png</file>
+        <file>images/non-visual-component@2x.png</file>
         <file>mockfiles/Window.qml</file>
         <file>mockfiles/SwipeView.qml</file>
         <file>mockfiles/GenericBackend.qml</file>