D3D12: Support QQuickItem::grabToImage

that is, the grabbing of layers. This is where things start getting
insane because now the convenient assumptions of updateTexture() for
layers only getting called in the sync phase before the rendering of the
real frame begins breaks down. With item grabbing the call happens on
afterRendering()... the engine will now do a minor hack when doing the
readback to make this work.

This, together with the previous patches provides us with the following
impressive, highly karma-boosting results:

tst_scenegraph 24 passed, 0 failed, 11 skipped
tst_qquickwindow 52 passed, 0 failed, 6 skipped
tst_qquickitem 61 passed, 0 failed, 0 skipped
tst_qquickitem2 84 passed, 0 failed, 6 skipped

Change-Id: I8f160e6848215a3b3304f2e00516eea0d96eb4a0
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 1 insertions, 2 deletions

diff --git a/src/quick/items/qquickitemgrabresult.cpp b/src/quick/items/qquickitemgrabresult.cpp
index 3ff61be241..f69b5b3f4b 100644
--- a/src/quick/items/qquickitemgrabresult.cpp
+++ b/src/quick/items/qquickitemgrabresult.cpp
@@ -240,8 +240,7 @@ void QQuickItemGrabResult::render()
         return;
 
     d->texture->setRect(QRectF(0, d->itemSize.height(), d->itemSize.width(), -d->itemSize.height()));
-    QSGContext *sg = QSGDefaultRenderContext::from(QOpenGLContext::currentContext())->sceneGraphContext();
-    const QSize minSize = sg->minimumFBOSize();
+    const QSize minSize = QQuickWindowPrivate::get(d->window.data())->context->sceneGraphContext()->minimumFBOSize();
     d->texture->setSize(QSize(qMax(minSize.width(), d->textureSize.width()),
                               qMax(minSize.height(), d->textureSize.height())));
     d->texture->scheduleUpdate();