Revert "Emit updateBlock signal in QTextDocumentLayout"

This reverts commit 13040043b2f2274de74c296ede7dd3e6ffb67dcb.
It introduced a bad regression, noticeable for longer documents, as
it would cause the documentChanged(0, length) to trigger a layout of
the entire document.

The bug report for the commit (or the commit itself) does not contain
a test case, but it is regardless the wrong approach. Note that
QQuickTextEdit already listens to the contentsChange signal and
invalidates the changed parts of the document as a reaction to this,
so it should already work as expected.

[ChangeLog][Qt Gui][Text] Fixed performance hit from showing large
QTextDocuments in a QTextEdit or QTextBrowser. (Regression introduced
in Qt 5.3.0)

Task-number: QTBUG-51411
Change-Id: I6e7fbf8f62a1d68779eef5da3781de14d9fdcad8
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 2 insertions, 5 deletions

diff --git a/src/gui/text/qtextdocumentlayout.cpp b/src/gui/text/qtextdocumentlayout.cpp
index 0c8904b4c5..8ad2d85e7c 100644
--- a/src/gui/text/qtextdocumentlayout.cpp
+++ b/src/gui/text/qtextdocumentlayout.cpp
@@ -2921,11 +2921,11 @@ void QTextDocumentLayout::documentChanged(int from, int oldLength, int length)
 {
     Q_D(QTextDocumentLayout);
 
-    QTextBlock startIt = document()->findBlock(from);
+    QTextBlock blockIt = document()->findBlock(from);
     QTextBlock endIt = document()->findBlock(qMax(0, from + length - 1));
     if (endIt.isValid())
         endIt = endIt.next();
-    for (QTextBlock blockIt = startIt; blockIt.isValid() && blockIt != endIt; blockIt = blockIt.next())
+     for (; blockIt.isValid() && blockIt != endIt; blockIt = blockIt.next())
          blockIt.clearLayout();
 
     if (d->docPrivate->pageSize.isNull())
@@ -2967,9 +2967,6 @@ void QTextDocumentLayout::documentChanged(int from, int oldLength, int length)
 
     d->insideDocumentChange = false;
 
-    for (QTextBlock blockIt = startIt; blockIt.isValid() && blockIt != endIt; blockIt = blockIt.next())
-         emit updateBlock(blockIt);
-
     if (d->showLayoutProgress) {
         const QSizeF newSize = dynamicDocumentSize();
         if (newSize != d->lastReportedSize) {