Fix updating of text nodes in QQuickTextEdit

The update algorithm wasn't correctly removing all node that
requires removing, as the startPosition is not always up to
date when deleting lines of code.

Instead, figure out the first Node after the changed region that
is clean and keep that one as a reference.

Amends 560a1991ac4524ff16352da23a2b54d717548f33.

Fixes: QTBUG-74745
Change-Id: I4a2c5bd7a673af5cad1850e3a5b703f9554cd7e6
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Igor Bugaev <freedbrt@gmail.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

1 files changed, 4 insertions, 5 deletions

diff --git a/src/quick/items/qquicktextedit.cpp b/src/quick/items/qquicktextedit.cpp
index ad1a6039c7..bdfbb979dd 100644
--- a/src/quick/items/qquicktextedit.cpp
+++ b/src/quick/items/qquicktextedit.cpp
@@ -2047,20 +2047,19 @@ QSGNode *QQuickTextEdit::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *
             firstDirtyPos = nodeIterator->startPos();
             // ### this could be optimized if the first and last dirty nodes are not connected
             // as the intermediate text nodes would usually only need to be transformed differently.
-            int lastDirtyPos = firstDirtyPos;
+            QQuickTextNode *firstCleanNode = nullptr;
             auto it = d->textNodeMap.constEnd();
             while (it != nodeIterator) {
                 --it;
-                if (it->dirty()) {
-                    lastDirtyPos = it->startPos();
+                if (it->dirty())
                     break;
-                }
+                firstCleanNode = it->textNode();
             }
             do {
                 rootNode->removeChildNode(nodeIterator->textNode());
                 delete nodeIterator->textNode();
                 nodeIterator = d->textNodeMap.erase(nodeIterator);
-            } while (nodeIterator != d->textNodeMap.constEnd() && nodeIterator->startPos() <= lastDirtyPos);
+            } while (nodeIterator != d->textNodeMap.constEnd() && nodeIterator->textNode() != firstCleanNode);
         }
 
         // FIXME: the text decorations could probably be handled separately (only updated for affected textFrames)