Fix QQuickCanvasItem::toImage() high-DPI capture

Make toImage() work for devicePixelRatio > 1 by
scaling the source rect.

Also set the devicePixelRatio on the returned image.

Task-number: QTBUG-59170
Change-Id: I0c8ccd562c1cf1e89ff37ca1806b46296480b0d0
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

2 files changed, 11 insertions, 8 deletions

diff --git a/src/quick/items/context2d/qquickcanvasitem.cpp b/src/quick/items/context2d/qquickcanvasitem.cpp
index da9379e7af..dab35f2a54 100644
--- a/src/quick/items/context2d/qquickcanvasitem.cpp
+++ b/src/quick/items/context2d/qquickcanvasitem.cpp
@@ -1104,14 +1104,17 @@ bool QQuickCanvasItem::isImageLoaded(const QUrl& url) const
 QImage QQuickCanvasItem::toImage(const QRectF& rect) const
 {
     Q_D(const QQuickCanvasItem);
-    if (d->context) {
-        if (rect.isEmpty())
-            return d->context->toImage(canvasWindow());
-        else
-            return d->context->toImage(rect);
-    }
 
-    return QImage();
+    if (!d->context)
+        return QImage();
+
+    const QRectF &rectSource = rect.isEmpty() ? canvasWindow() : rect;
+    const qreal dpr = window() ? window()->effectiveDevicePixelRatio() : qreal(1);
+    const QRectF rectScaled(rectSource.topLeft() * dpr, rectSource.size() * dpr);
+
+    QImage image = d->context->toImage(rectScaled);
+    image.setDevicePixelRatio(dpr);
+    return image;
 }
 
 static const char* mimeToType(const QString &mime)
diff --git a/src/quick/items/context2d/qquickcontext2d.cpp b/src/quick/items/context2d/qquickcontext2d.cpp
index ce890771d9..0a7db7fa97 100644
--- a/src/quick/items/context2d/qquickcontext2d.cpp
+++ b/src/quick/items/context2d/qquickcontext2d.cpp
@@ -962,7 +962,7 @@ static QV4::ReturnedValue qt_create_image_data(qreal w, qreal h, QV4::ExecutionE
         *pixelData->d()->image = QImage(w, h, QImage::Format_ARGB32);
         pixelData->d()->image->fill(0x00000000);
     } else {
-        Q_ASSERT(image.width() == qRound(w) && image.height() == qRound(h));
+        Q_ASSERT(image.width()== qRound(w * image.devicePixelRatio()) && image.height() == qRound(h * image.devicePixelRatio()));
         *pixelData->d()->image = image.format() == QImage::Format_ARGB32 ? image : image.convertToFormat(QImage::Format_ARGB32);
     }