Add option to disable emoji parsing

There is a very small overhead to this, so we provide a
way to manually disable it if you know you are displaying
text without any emoji sequences.

Task-number: QTBUG-111801
Change-Id: I231b3dfab368ef2cf3b17dd57cd4e3160ed38192
Reviewed-by: Lars Knoll <lars@knoll.priv.no>

src/gui/text/qtextengine.cpp

@@ -1956,7 +1956,6 @@ namespace {
 
 void QTextEngine::itemize() const
 {
-    static bool disableEmojiSegmenter = qEnvironmentVariableIntValue("QT_DISABLE_EMOJI_SEGMENTER") > 0;
     validate();
     if (layoutData->items.size())
         return;
@@ -1987,6 +1986,9 @@ void QTextEngine::itemize() const
     }
 
 #if !defined(QT_NO_EMOJISEGMENTER)
+    static const bool sDisableEmojiSegmenter = qEnvironmentVariableIntValue("QT_DISABLE_EMOJI_SEGMENTER") > 0;
+    const bool disableEmojiSegmenter = sDisableEmojiSegmenter || option.flags().testFlag(QTextOption::DisableEmojiParsing);
+
     QVarLengthArray<CharacterCategory> categorizedString;
     if (!disableEmojiSegmenter) {
         // Parse emoji sequences

src/gui/text/qtextoption.cpp

@@ -272,6 +272,9 @@ QList<QTextOption::Tab> QTextOption::tabs() const
   \value AddSpaceForLineAndParagraphSeparators While determining the line-break positions take into account the
             space added for drawing a separator character.
   \value SuppressColors Suppress all color changes in the character formats (except the main selection).
+  \value [since 6.9] DisableEmojiParsing By default, Qt will detect emoji sequences in input strings
+    and prioritize using color fonts to display them. This extra step can be disabled by setting the
+    DisableEmojiParsing flag if it is known in advance that it will not be needed.
 */
 
 /*!

src/gui/text/qtextoption.h

@@ -74,6 +74,7 @@ public:
         SuppressColors = 0x8,
         ShowDocumentTerminator = 0x10,
         ShowDefaultIgnorables = 0x20,
+        DisableEmojiParsing = 0x40,
         IncludeTrailingSpaces = 0x80000000,
     };
     Q_DECLARE_FLAGS(Flags, Flag)

tests/baseline/text/tst_baseline_text.cpp

@@ -19,6 +19,8 @@ private slots:
     void tst_render();
     void tst_differentScriptsBackgrounds();
     void tst_synthesizedObliqueAndRotation();
+    void tst_disableEmojiParsing_data();
+    void tst_disableEmojiParsing();
 
 private:
     QDir htmlDir;
@@ -126,6 +128,57 @@ void tst_Text::tst_synthesizedObliqueAndRotation()
     QBASELINE_CHECK(image, "tst_synthesizedObliqueAndRotation");
 }
 
+void tst_Text::tst_disableEmojiParsing_data()
+{
+    QTest::addColumn<QString>("html");
+
+    QStringList htmlFiles;
+    // first add generic test files
+    for (const auto &qssFile : htmlDir.entryList({QStringLiteral("emoji*.html")}, QDir::Files | QDir::Readable))
+        htmlFiles << htmlDir.absoluteFilePath(qssFile);
+
+    // then test-function specific files
+    const QString testFunction = QString(QTest::currentTestFunction()).remove("tst_").toLower();
+    if (htmlDir.cd(testFunction)) {
+        for (const auto &htmlFile : htmlDir.entryList({QStringLiteral("*.html")}, QDir::Files | QDir::Readable))
+            htmlFiles << htmlDir.absoluteFilePath(htmlFile);
+        htmlDir.cdUp();
+    }
+
+    for (const auto &htmlFile : htmlFiles) {
+        QFileInfo fileInfo(htmlFile);
+        QFile file(htmlFile);
+        QVERIFY(file.open(QFile::ReadOnly));
+        QString html = QString::fromUtf8(file.readAll());
+        QBaselineTest::newRow(fileInfo.baseName().toUtf8()) << html;
+    }
+}
+
+void tst_Text::tst_disableEmojiParsing()
+{
+    QFETCH(QString, html);
+
+    QTextDocument textDocument;
+    textDocument.setPageSize(QSizeF(800, 600));
+    textDocument.setHtml(html);
+
+    QTextOption opt = textDocument.defaultTextOption();
+    opt.setFlags(QTextOption::DisableEmojiParsing);
+    textDocument.setDefaultTextOption(opt);
+
+    QImage image(800, 600, QImage::Format_ARGB32);
+    image.fill(Qt::white);
+
+    {
+        QPainter painter(&image);
+
+        QAbstractTextDocumentLayout::PaintContext context;
+        context.palette.setColor(QPalette::Text, Qt::black);
+        textDocument.documentLayout()->draw(&painter, context);
+    }
+
+    QBASELINE_CHECK(image, "tst_disableEmojiParsing");
+}
 
 QBASELINETEST_MAIN(tst_Text)