Fix QPlainTextEdit painting errors

With line wrapping enabled and very large text blocks, painting errors
could occur.

Reviewed-by: hjk
(cherry picked from commit 82dba1d346a6f4a5d2602d930e0aed75c13bcafb)

1 files changed, 3 insertions, 2 deletions

diff --git a/src/gui/widgets/qplaintextedit.cpp b/src/gui/widgets/qplaintextedit.cpp
index 20de404803..03c36d716d 100644
--- a/src/gui/widgets/qplaintextedit.cpp
+++ b/src/gui/widgets/qplaintextedit.cpp
@@ -573,7 +573,8 @@ QRectF QPlainTextEditControl::blockBoundingRect(const QTextBlock &block) const {
     if (!block.isValid())
         return QRectF();
     QRectF r = documentLayout->blockBoundingRect(currentBlock);
-    while (currentBlockNumber < blockNumber && offset.y() <= 2* textEdit->viewport()->height()) {
+    int maxVerticalOffset = r.height();
+    while (currentBlockNumber < blockNumber && offset.y() - maxVerticalOffset <= 2* textEdit->viewport()->height()) {
         offset.ry() += r.height();
         currentBlock = currentBlock.next();
         ++currentBlockNumber;
@@ -583,7 +584,7 @@ QRectF QPlainTextEditControl::blockBoundingRect(const QTextBlock &block) const {
         }
         r = documentLayout->blockBoundingRect(currentBlock);
     }
-    while (currentBlockNumber > blockNumber && offset.y() >= -textEdit->viewport()->height()) {
+    while (currentBlockNumber > blockNumber && offset.y() + maxVerticalOffset >= -textEdit->viewport()->height()) {
         currentBlock = currentBlock.previous();
         --currentBlockNumber;
         while (!currentBlock.isVisible()) {