From 88d759d50f6bacaa48100be3edf5a5d5130da1b2 Mon Sep 17 00:00:00 2001
From: Eike Ziller <eike.ziller@qt.io>
Date: Tue, 24 Sep 2019 13:51:41 +0200
Subject: [PATCH] Help/litehtml: Keep top position also when zooming

Change-Id: I65e12d4fca33719bc1a3ae08f7871d08d8d9c449
Reviewed-by: hjk <hjk@qt.io>
---
 .../help/qlitehtml/qlitehtmlwidget.cpp        | 31 ++++++++++++-------
 src/plugins/help/qlitehtml/qlitehtmlwidget.h  |  1 +
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/plugins/help/qlitehtml/qlitehtmlwidget.cpp b/src/plugins/help/qlitehtml/qlitehtmlwidget.cpp
index 1196e698ada..509bf3602ff 100644
--- a/src/plugins/help/qlitehtml/qlitehtmlwidget.cpp
+++ b/src/plugins/help/qlitehtml/qlitehtmlwidget.cpp
@@ -439,7 +439,7 @@ void QLiteHtmlWidget::setZoomFactor(qreal scale)
 {
     Q_ASSERT(scale != 0);
     d->zoomFactor = scale;
-    render();
+    withFixedTextPosition([this] { render(); });
 }
 
 qreal QLiteHtmlWidget::zoomFactor() const
@@ -559,17 +559,10 @@ static litehtml::element::ptr elementForY(int y, const litehtml::document::ptr &
 
 void QLiteHtmlWidget::resizeEvent(QResizeEvent *event)
 {
-    // remember element to which to scroll after re-rendering
-    QPoint viewportPos;
-    QPoint pos;
-    htmlPos({}, &viewportPos, &pos); // top-left
-    const litehtml::element::ptr element = elementForY(pos.y(), d->documentContainer.document());
-    QAbstractScrollArea::resizeEvent(event);
-    render();
-    if (element) {
-        verticalScrollBar()->setValue(
-            std::min(element->get_placement().y, verticalScrollBar()->maximum()));
-    }
+    withFixedTextPosition([this, event] {
+        QAbstractScrollArea::resizeEvent(event);
+        render();
+    });
 }
 
 void QLiteHtmlWidget::mouseMoveEvent(QMouseEvent *event)
@@ -625,6 +618,20 @@ void QLiteHtmlWidget::contextMenuEvent(QContextMenuEvent *event)
     emit contextMenuRequested(event->pos(), d->documentContainer.linkAt(pos, viewportPos));
 }
 
+void QLiteHtmlWidget::withFixedTextPosition(const std::function<void()> &action)
+{
+    // remember element to which to scroll after re-rendering
+    QPoint viewportPos;
+    QPoint pos;
+    htmlPos({}, &viewportPos, &pos); // top-left
+    const litehtml::element::ptr element = elementForY(pos.y(), d->documentContainer.document());
+    action();
+    if (element) {
+        verticalScrollBar()->setValue(
+            std::min(element->get_placement().y, verticalScrollBar()->maximum()));
+    }
+}
+
 void QLiteHtmlWidget::render()
 {
     if (!d->documentContainer.document())
diff --git a/src/plugins/help/qlitehtml/qlitehtmlwidget.h b/src/plugins/help/qlitehtml/qlitehtmlwidget.h
index 97f5be6c63b..a79e5824b0c 100644
--- a/src/plugins/help/qlitehtml/qlitehtmlwidget.h
+++ b/src/plugins/help/qlitehtml/qlitehtmlwidget.h
@@ -77,6 +77,7 @@ protected:
     void contextMenuEvent(QContextMenuEvent *event) override;
 
 private:
+    void withFixedTextPosition(const std::function<void()> &action);
     void render();
     QPoint scrollPosition() const;
     void htmlPos(const QPoint &pos, QPoint *viewportPos, QPoint *htmlPos) const;