From bc711e755cc64ba443fd0c252771e6d5152bf27e Mon Sep 17 00:00:00 2001
From: Le Tan <tamlokveer@gmail.com>
Date: Wed, 26 Sep 2018 19:24:18 +0800
Subject: [PATCH] VTextDocumentLayout: bug fix in relayout()

---
 src/vtextdocumentlayout.cpp | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/src/vtextdocumentlayout.cpp b/src/vtextdocumentlayout.cpp
index 8acab03b..a6f92e77 100644
--- a/src/vtextdocumentlayout.cpp
+++ b/src/vtextdocumentlayout.cpp
@@ -557,7 +557,7 @@ void VTextDocumentLayout::updateOffsetBefore(const QTextBlock &p_block)
             blk = blk.next();
             while (blk.isValid() && blk.blockNumber() <= blockNum) {
                 BlockLayoutInfo *ninfo = VTextBlockData::layoutInfo(blk);
-                Q_ASSERT(!ninfo->isNull());
+                V_ASSERT(!ninfo->isNull());
                 ninfo->m_offset = offset;
                 offset = ninfo->bottom();
                 blk = blk.next();
@@ -570,6 +570,8 @@ void VTextDocumentLayout::updateOffsetBefore(const QTextBlock &p_block)
     }
 }
 
+// NOTICE: It will skip non-layouted or offset-non-changed blocks.
+// So if you relayout separated blocks, you need to updateOffsetAfter() for each of them.
 void VTextDocumentLayout::updateOffsetAfter(const QTextBlock &p_block)
 {
     BlockLayoutInfo *info = VTextBlockData::layoutInfo(p_block);
@@ -975,28 +977,31 @@ void VTextDocumentLayout::relayout(const OrderedIntSet &p_blocks)
     QTextDocument *doc = document();
 
     // Need to relayout and update blocks in ascending order.
-    QTextBlock startBlock;
+    QVector<QTextBlock> blocks;
+    blocks.reserve(p_blocks.size());
     for (auto bn = p_blocks.keyBegin(); bn != p_blocks.keyEnd(); ++bn) {
         QTextBlock block = doc->findBlockByNumber(*bn);
         if (block.isValid()) {
-            if (!startBlock.isValid()) {
-                startBlock = block;
-            }
-
+            blocks.append(block);
             clearBlockLayout(block);
             layoutBlock(block);
         }
     }
 
-    if (!startBlock.isValid()) {
+    if (blocks.isEmpty()) {
         return;
     }
 
-    updateOffset(startBlock);
+    // Need to update offset for each of these discontinuous blocks, because
+    // the offset of the non-touched blocks may be the same but there are still
+    // touched blocks after them.
+    for (auto & blk : blocks) {
+        updateOffset(blk);
+    }
 
     updateDocumentSize();
 
-    qreal offset = VTextBlockData::layoutInfo(startBlock)->m_offset;
+    qreal offset = VTextBlockData::layoutInfo(blocks.first())->m_offset;
     emit update(QRectF(0., offset, 1000000000., 1000000000.));
 }