Fix disappearing nodes when adding in two levels of batch root

When having e.g. a clip node inside another clip node and adding
children to the innermost, we would get into the situation where
we did a partial rebuild for the outermost root, but its available
render order count would not be updated to reflect the change
deeper down in the tree. Since the z range would be based on the
outermost batch root's knowledge of the maximum render order in
the tree, what would happen is that the z of the rendered nodes
would increase steadily until they went outside of the viewing
volume and disappeared.

When decreasing the available order count of a batch root, we need
to also decrease the available order count of its parents. If any
of them drop below zero, we need to rebuild the render lists.

[ChangeLog][QtQuick] Fixed nodes sometimes disappearing when
adding many new nodes to the tree.

Change-Id: I39c34acf0e1e0e87601f0fcd983f8da38cee029f
Task-number: QTBUG-42096
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

1 files changed, 12 insertions, 6 deletions

diff --git a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
index 838251ed08..2f94bad75d 100644
--- a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
+++ b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
@@ -460,12 +460,18 @@ void Updater::visitGeometryNode(Node *n)
 
         if (e->root) {
             BatchRootInfo *info = renderer->batchRootInfo(e->root);
-            info->availableOrders--;
-            if (info->availableOrders < 0) {
-                renderer->m_rebuild |= Renderer::BuildRenderLists;
-            } else {
-                renderer->m_rebuild |= Renderer::BuildRenderListsForTaggedRoots;
-                renderer->m_taggedRoots << e->root;
+            while (info != 0) {
+                info->availableOrders--;
+                if (info->availableOrders < 0) {
+                    renderer->m_rebuild |= Renderer::BuildRenderLists;
+                } else {
+                    renderer->m_rebuild |= Renderer::BuildRenderListsForTaggedRoots;
+                    renderer->m_taggedRoots << e->root;
+                }
+                if (info->parentRoot != 0)
+                    info = renderer->batchRootInfo(info->parentRoot);
+                else
+                    info = 0;
             }
         } else {
             renderer->m_rebuild |= Renderer::FullRebuild;