Fix page breaking with large images

Don't go into an infinite loop breaking pages, when an image is about
as large as the page. Correctly take top and bottom margins into account
when calculating whether the image could fit on one page.

Amends change 416b4cf685030114837bd375664fd12047895a62.

Fixes: QTBUG-73730
Change-Id: Id311ddf05510be3b1d131702f4e17025a9861e58
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 64 insertions, 1 deletions

diff --git a/src/gui/text/qtextdocumentlayout.cpp b/src/gui/text/qtextdocumentlayout.cpp
index 2e1a2b5bff..bed0a2c450 100644
--- a/src/gui/text/qtextdocumentlayout.cpp
+++ b/src/gui/text/qtextdocumentlayout.cpp
@@ -145,6 +145,9 @@ struct QTextLayoutStruct {
     inline QFixed absoluteY() const
     { return frameY + y; }
 
+    inline QFixed contentHeight() const
+    { return pageHeight - pageBottomMargin - pageTopMargin; }
+
     inline int currentPage() const
     { return pageHeight == 0 ? 0 : (absoluteY() / pageHeight).truncate(); }
 
@@ -2701,7 +2704,7 @@ void QTextDocumentLayoutPrivate::layoutBlock(const QTextBlock &bl, int blockPosi
             getLineHeightParams(blockFormat, line, scaling, &lineAdjustment, &lineBreakHeight, &lineHeight, &lineBottom);
 
             while (layoutStruct->pageHeight > 0 && layoutStruct->absoluteY() + lineBreakHeight > layoutStruct->pageBottom &&
-                layoutStruct->pageHeight >= lineBreakHeight) {
+                layoutStruct->contentHeight() >= lineBreakHeight) {
                 layoutStruct->newPage();
 
                 floatMargins(layoutStruct->y, layoutStruct, &left, &right);
diff --git a/tests/auto/gui/text/qtextdocumentlayout/tst_qtextdocumentlayout.cpp b/tests/auto/gui/text/qtextdocumentlayout/tst_qtextdocumentlayout.cpp
index c79f787547..f66b16b970 100644
--- a/tests/auto/gui/text/qtextdocumentlayout/tst_qtextdocumentlayout.cpp
+++ b/tests/auto/gui/text/qtextdocumentlayout/tst_qtextdocumentlayout.cpp
@@ -59,6 +59,8 @@ private slots:
     void imageAtRightAlignedTab();
     void blockVisibility();
 
+    void largeImage();
+
 private:
     QTextDocument *doc;
 };
@@ -347,5 +349,63 @@ void tst_QTextDocumentLayout::blockVisibility()
     QCOMPARE(doc->size(), halfSize);
 }
 
+void tst_QTextDocumentLayout::largeImage()
+{
+     auto img = QImage(400, 500, QImage::Format_ARGB32_Premultiplied);
+     img.fill(Qt::black);
+
+     {
+         QTextDocument document;
+
+         document.addResource(QTextDocument::ImageResource,
+                 QUrl("data://test.png"), QVariant(img));
+         document.setPageSize({500, 504});
+
+         auto html = "<img src=\"data://test.png\">";
+         document.setHtml(html);
+
+         QCOMPARE(document.pageCount(), 2);
+     }
+
+     {
+         QTextDocument document;
+
+         document.addResource(QTextDocument::ImageResource,
+                 QUrl("data://test.png"), QVariant(img));
+         document.setPageSize({500, 508});
+
+         auto html = "<img src=\"data://test.png\">";
+         document.setHtml(html);
+
+         QCOMPARE(document.pageCount(), 1);
+     }
+
+     {
+         QTextDocument document;
+
+         document.addResource(QTextDocument::ImageResource,
+                 QUrl("data://test.png"), QVariant(img));
+         document.setPageSize({585, 250});
+
+         auto html = "<img src=\"data://test.png\">";
+         document.setHtml(html);
+
+         QCOMPARE(document.pageCount(), 3);
+     }
+
+     {
+         QTextDocument document;
+
+         document.addResource(QTextDocument::ImageResource,
+                 QUrl("data://test.png"), QVariant(img));
+         document.setPageSize({585, 258});
+
+         auto html = "<img src=\"data://test.png\">";
+         document.setHtml(html);
+
+         QCOMPARE(document.pageCount(), 2);
+     }
+}
+
 QTEST_MAIN(tst_QTextDocumentLayout)
 #include "tst_qtextdocumentlayout.moc"