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>

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);
 

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>

src/plugins/qmldesigner/designercore/instances/nodeinstanceview.cpp

@@ -1496,7 +1496,11 @@ void NodeInstanceView::handlePuppetToCreatorCommand(const PuppetToCreatorCommand
         if (hasModelNodeForInternalId(container.instanceId()) && !image.isNull()) {
             auto node = modelNodeForInternalId(container.instanceId());
             if (node.isValid()) {
-                image.setDevicePixelRatio(2.);
+                const double ratio = QmlDesignerPlugin::formEditorDevicePixelRatio();
+                const int dim = Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * ratio;
+                if (image.height() != dim || image.width() != dim)
+                    image = image.scaled(dim, dim, Qt::KeepAspectRatio);
+                image.setDevicePixelRatio(ratio);
                 updatePreviewImageForNode(node, image);
             }
         }
@@ -1540,12 +1544,10 @@ void NodeInstanceView::requestModelNodePreviewImage(const ModelNode &node, const
             } else if (node.isComponent()) {
                 componentPath = node.metaInfo().componentFileName();
             }
+            const int dim = Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * QmlDesignerPlugin::formEditorDevicePixelRatio();
             m_nodeInstanceServer->requestModelNodePreviewImage(
-                        RequestModelNodePreviewImageCommand(
+                        RequestModelNodePreviewImageCommand(instance.instanceId(), QSize(dim, dim),
-                            instance.instanceId(),
+                                                            componentPath, renderItemId));
-                            QSize(Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS,
-                                  Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS),
-                            componentPath, renderItemId));
         }
     }
 }
@@ -1587,6 +1589,7 @@ QVariant NodeInstanceView::previewImageDataForImageNode(const ModelNode &modelNo
     ModelNodePreviewImageData imageData;
     imageData.id = modelNode.id();
     imageData.type = QString::fromLatin1(modelNode.type());
+    const double ratio = QmlDesignerPlugin::formEditorDevicePixelRatio();
 
     if (imageSource.isEmpty() && modelNode.isSubclassOf("QtQuick3D.Texture")) {
         // Texture node may have sourceItem instead
@@ -1601,11 +1604,10 @@ QVariant NodeInstanceView::previewImageDataForImageNode(const ModelNode &modelNo
                     return previewImageDataForGenericNode(modelNode, boundNode);
                 } else {
                     QmlItemNode itemNode(boundNode);
-                    imageData.pixmap = itemNode.instanceRenderPixmap().scaled(
+                    const int dim = Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * ratio;
-                                Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * 2,
+                    imageData.pixmap = itemNode.instanceRenderPixmap().scaled(dim, dim, Qt::KeepAspectRatio);
-                                Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * 2,
+                    imageData.pixmap.setDevicePixelRatio(ratio);
-                                Qt::KeepAspectRatio);
+
-                    imageData.pixmap.setDevicePixelRatio(2.);
                 }
                 imageData.info = QObject::tr("Source item: %1").arg(boundNode.id());
             }
@@ -1629,10 +1631,9 @@ QVariant NodeInstanceView::previewImageDataForImageNode(const ModelNode &modelNo
             QPixmap originalPixmap;
             originalPixmap.load(imageSource);
             if (!originalPixmap.isNull()) {
-                imageData.pixmap = originalPixmap.scaled(Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * 2,
+                const int dim = Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * ratio;
-                                                         Constants::MODELNODE_PREVIEW_IMAGE_DIMENSIONS * 2,
+                imageData.pixmap = originalPixmap.scaled(dim, dim, Qt::KeepAspectRatio);
-                                                         Qt::KeepAspectRatio);
+                imageData.pixmap.setDevicePixelRatio(ratio);
-                imageData.pixmap.setDevicePixelRatio(2.);
 
                 double imgSize = double(imageFi.size());
                 static QStringList units({QObject::tr("B"), QObject::tr("KB"), QObject::tr("MB"), QObject::tr("GB")});