Fix convertToFormat with color-tables

The function was only well defined from RGB32 and ARGB32PM formats,
this patch fixes it so it behaves well from all formats.

Task-number: QTBUG-63163
Change-Id: Id892531d9aaf997b707b430196c1166493792a2a
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

2 files changed, 19 insertions, 17 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index b2e5ac93b1..43b77a862d 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -2096,8 +2096,8 @@ static QImage convertWithPalette(const QImage &src, QImage::Format format,
     Returns a copy of the image converted to the given \a format,
     using the specified \a colorTable.
 
-    Conversion from 32 bit to 8 bit indexed is a slow operation and
-    will use a straightforward nearest color approach, with no
+    Conversion from RGB formats to indexed formats is a slow operation
+    and will use a straightforward nearest color approach, with no
     dithering.
 */
 QImage QImage::convertToFormat(Format format, const QVector<QRgb> &colorTable, Qt::ImageConversionFlags flags) const
@@ -2105,23 +2105,12 @@ QImage QImage::convertToFormat(Format format, const QVector<QRgb> &colorTable, Q
     if (!d || d->format == format)
         return *this;
 
-    if (format <= QImage::Format_Indexed8 && depth() == 32) {
-        return convertWithPalette(*this, format, colorTable);
-    }
-
-    const Image_Converter *converterPtr = &qimage_converter_map[d->format][format];
-    Image_Converter converter = *converterPtr;
-    if (!converter)
+    if (format == QImage::Format_Invalid)
         return QImage();
+    if (format <= QImage::Format_Indexed8)
+        return convertWithPalette(convertToFormat(QImage::Format_ARGB32, flags), format, colorTable);
 
-    QImage image(d->width, d->height, format);
-    QIMAGE_SANITYCHECK_MEMORY(image);
-
-    image.d->offset = offset();
-    copyMetadata(image.d, d);
-
-    converter(image.d, d, flags);
-    return image;
+    return convertToFormat(format, flags);
 }
 
 /*!
diff --git a/tests/auto/gui/image/qimage/tst_qimage.cpp b/tests/auto/gui/image/qimage/tst_qimage.cpp
index fac785ac86..73e11e7cc7 100644
--- a/tests/auto/gui/image/qimage/tst_qimage.cpp
+++ b/tests/auto/gui/image/qimage/tst_qimage.cpp
@@ -69,6 +69,7 @@ private slots:
 
     void convertToFormat_data();
     void convertToFormat();
+    void convertToFormatWithColorTable();
 
     void convertToFormatRgb888ToRGB32();
 
@@ -958,6 +959,18 @@ void tst_QImage::convertToFormat()
     QFile::remove(QLatin1String("expected2.xpm"));
 }
 
+void tst_QImage::convertToFormatWithColorTable()
+{
+    QVector<QRgb> colors(2);
+    colors[0] = 0xFF000000;
+    colors[1] = 0xFFFFFFFF;
+    for (int format = QImage::Format_RGB32; format < QImage::Format_Alpha8; ++format) {
+        QImage fromImage(10, 10, (QImage::Format)format);
+        QImage bitmap = fromImage.convertToFormat(QImage::Format_Mono, colors);
+        QVERIFY(!bitmap.isNull());
+    }
+}
+
 void tst_QImage::convertToFormatRgb888ToRGB32()
 {
     // 545 so width % 4 != 0. This ensure there is padding at the end of the scanlines