From b3cdd63d4bdaea09222fb93ffcd5104a2dc0bf2e Mon Sep 17 00:00:00 2001
From: Eirik Aavitsland <eirik.aavitsland@qt.io>
Date: Tue, 21 Apr 2020 15:04:15 +0200
Subject: Assistant: keep text at the top visible when resizing

After following a link to look up a keyword, resizing the width of the
window would lead to the looked-up position being scroled away.  This
fix is adapted from the corresponding fix in Qt Creator,
https://codereview.qt-project.org/c/qt-creator/qt-creator/+/274996

Fixes: QTBUG-34525
Change-Id: Ia9c2aab4b2c8039965eff098ff51dbdcc4967a01
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
---
 src/assistant/assistant/helpviewer.h       |  2 ++
 src/assistant/assistant/helpviewer_qtb.cpp | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/src/assistant/assistant/helpviewer.h b/src/assistant/assistant/helpviewer.h
index 667fa05a4..fa954cc9f 100644
--- a/src/assistant/assistant/helpviewer.h
+++ b/src/assistant/assistant/helpviewer.h
@@ -130,6 +130,7 @@ protected:
     void wheelEvent(QWheelEvent *event) override;
     void mousePressEvent(QMouseEvent *event) override;
     void mouseReleaseEvent(QMouseEvent *event) override;
+    void resizeEvent(QResizeEvent *e) override;
 
 private slots:
     void actionChanged();
@@ -141,6 +142,7 @@ private:
     void contextMenuEvent(QContextMenuEvent *event) override;
     QVariant loadResource(int type, const QUrl &name) TEXTBROWSER_OVERRIDE;
     bool handleForwardBackwardMouseButtons(QMouseEvent *e);
+    void scrollToTextPosition(int position);
 
 private:
     HelpViewerPrivate *d;
diff --git a/src/assistant/assistant/helpviewer_qtb.cpp b/src/assistant/assistant/helpviewer_qtb.cpp
index f9bdddb52..260dbfc1d 100644
--- a/src/assistant/assistant/helpviewer_qtb.cpp
+++ b/src/assistant/assistant/helpviewer_qtb.cpp
@@ -38,6 +38,7 @@
 
 #include <QtGui/QContextMenuEvent>
 #include <QtWidgets/QMenu>
+#include <QtWidgets/QScrollBar>
 #ifndef QT_NO_CLIPBOARD
 #include <QtGui/QClipboard>
 #endif
@@ -312,6 +313,14 @@ void HelpViewer::mouseReleaseEvent(QMouseEvent *e)
     QTextBrowser::mouseReleaseEvent(e);
 }
 
+
+void HelpViewer::resizeEvent(QResizeEvent *e)
+{
+    const int topTextPosition = cursorForPosition({width() / 2, 0}).position();
+    QTextBrowser::resizeEvent(e);
+    scrollToTextPosition(topTextPosition);
+}
+
 // -- private slots
 
 void HelpViewer::actionChanged()
@@ -377,4 +386,16 @@ QVariant HelpViewer::loadResource(int type, const QUrl &name)
     return ba;
 }
 
+
+void HelpViewer::scrollToTextPosition(int position)
+{
+    QTextCursor tc(document());
+    tc.setPosition(position);
+    const int dy = cursorRect(tc).top();
+    if (verticalScrollBar()) {
+        verticalScrollBar()->setValue(
+                    std::min(verticalScrollBar()->value() + dy, verticalScrollBar()->maximum()));
+    }
+}
+
 QT_END_NAMESPACE
-- 
cgit v1.2.3