webp handler: support alpha-less reading and writing

Webp files can be with or without alpha channel. The handler would
ignore this and read all as Format_ARGB32 images, and write all as
having alpha, in both cases losing that important bit of information.

As a driveby, simplify the endianness handling in write(). By always
converting the source image to an endianness-independent QImage
format, no special handling is required.

Task-number: QTBUG-48628
Change-Id: I624ed72b18a8b59a542979efcb4e8ff81214e0d7
Reviewed-by: Liang Qi <liang.qi@qt.io>

src/plugins/imageformats/webp/qwebphandler.cpp

@@ -174,7 +174,8 @@ bool QWebpHandler::read(QImage *image)
     if (status != VP8_STATUS_OK)
         return false;
 
-    QImage frame(m_iter.width, m_iter.height, QImage::Format_ARGB32);
+    QImage::Format format = m_features.has_alpha ? QImage::Format_ARGB32 : QImage::Format_RGB32;
+    QImage frame(m_iter.width, m_iter.height, format);
     uint8_t *output = frame.bits();
     size_t output_size = frame.sizeInBytes();
 #if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
@@ -219,13 +220,10 @@ bool QWebpHandler::write(const QImage &image)
     }
 
     QImage srcImage = image;
-#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
+    bool alpha = srcImage.hasAlphaChannel();
-    if (srcImage.format() != QImage::Format_ARGB32)
+    QImage::Format newFormat = alpha ? QImage::Format_RGBA8888 : QImage::Format_RGB888;
-        srcImage = srcImage.convertToFormat(QImage::Format_ARGB32);
+    if (srcImage.format() != newFormat)
-#else /* Q_BIG_ENDIAN */
+        srcImage = srcImage.convertToFormat(newFormat);
-    if (srcImage.format() != QImage::Format_RGBA8888)
-        srcImage = srcImage.convertToFormat(QImage::Format_RGBA8888);
-#endif
 
     WebPPicture picture;
     WebPConfig config;
@@ -238,13 +236,14 @@ bool QWebpHandler::write(const QImage &image)
     picture.width = srcImage.width();
     picture.height = srcImage.height();
     picture.use_argb = 1;
-#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN
+    bool failed = false;
-    if (!WebPPictureImportBGRA(&picture, srcImage.bits(), srcImage.bytesPerLine())) {
+    if (alpha)
-#else /* Q_BIG_ENDIAN */
+        failed = !WebPPictureImportRGBA(&picture, srcImage.bits(), srcImage.bytesPerLine());
-    if (!WebPPictureImportRGBA(&picture, srcImage.bits(), srcImage.bytesPerLine())) {
+    else
-#endif
+        failed = !WebPPictureImportRGB(&picture, srcImage.bits(), srcImage.bytesPerLine());
-        qWarning() << "failed to import image data to webp picture.";
 
+    if (failed) {
+        qWarning() << "failed to import image data to webp picture.";
         WebPPictureFree(&picture);
         return false;
     }

tests/auto/webp/tst_qwebp.cpp

@@ -53,15 +53,18 @@ void tst_qwebp::readImage_data()
 {
     QTest::addColumn<QString>("fileName");
     QTest::addColumn<QSize>("size");
+    QTest::addColumn<bool>("alpha");
 
-    QTest::newRow("kollada") << QString("kollada") << QSize(436, 160);
+    QTest::newRow("kollada") << QString("kollada") << QSize(436, 160) << true;
-    QTest::newRow("kollada_lossless") << QString("kollada_lossless") << QSize(436, 160);
+    QTest::newRow("kollada_lossless") << QString("kollada_lossless") << QSize(436, 160) << true;
+    QTest::newRow("kollada_noalpha") << QString("kollada_noalpha") << QSize(436, 160) << false;
 }
 
 void tst_qwebp::readImage()
 {
     QFETCH(QString, fileName);
     QFETCH(QSize, size);
+    QFETCH(bool, alpha);
 
     const QString path = QStringLiteral(":/images/") + fileName + QStringLiteral(".webp");
     QImageReader reader(path);
@@ -69,6 +72,7 @@ void tst_qwebp::readImage()
     QImage image = reader.read();
     QVERIFY2(!image.isNull(), qPrintable(reader.errorString()));
     QCOMPARE(image.size(), size);
+    QCOMPARE(image.hasAlphaChannel(), alpha);
 }
 
 void tst_qwebp::readAnimation_data()
@@ -136,10 +140,13 @@ void tst_qwebp::writeImage_data()
     QTest::addColumn<QString>("postfix");
     QTest::addColumn<int>("quality");
     QTest::addColumn<QSize>("size");
+    QTest::addColumn<bool>("alpha");
     QTest::addColumn<bool>("needcheck");
 
-    QTest::newRow("kollada-75") << QString("kollada") << QString(".png") << 75 << QSize(436, 160) << false;
+    QTest::newRow("kollada-75") << QString("kollada") << QString(".png") << 75 << QSize(436, 160) << true << false;
-    QTest::newRow("kollada-100") << QString("kollada") << QString(".png") << 100 << QSize(436, 160) << true;
+    QTest::newRow("kollada-100") << QString("kollada") << QString(".png") << 100 << QSize(436, 160) << true << true;
+    QTest::newRow("kollada_noalpha-75") << QString("kollada_noalpha") << QString(".webp") << 75 << QSize(436, 160) << false << false;
+    QTest::newRow("kollada_noalpha-100") << QString("kollada_noalpha") << QString(".webp") << 100 << QSize(436, 160) << false << true;
 }
 
 void tst_qwebp::writeImage()
@@ -148,6 +155,7 @@ void tst_qwebp::writeImage()
     QFETCH(QString, postfix);
     QFETCH(int, quality);
     QFETCH(QSize, size);
+    QFETCH(bool, alpha);
     QFETCH(bool, needcheck);
 
     const QString path = QString("%1-%2.webp").arg(fileName).arg(quality);
@@ -162,8 +170,13 @@ void tst_qwebp::writeImage()
     writer.setQuality(quality);
     QVERIFY2(writer.write(image), qPrintable(writer.errorString()));
 
+    QImage reread(path);
+    QVERIFY(!reread.isNull());
+    QVERIFY(reread.size() == size);
+    QVERIFY(reread.hasAlphaChannel() == alpha);
+
     if (needcheck)
-        QVERIFY(image == QImage(path));
+        QVERIFY(image == reread);
 }
 
 QTEST_MAIN(tst_qwebp)

tests/auto/webp/webp.qrc

@@ -4,5 +4,6 @@
         <file>images/kollada.webp</file>
         <file>images/kollada_lossless.webp</file>
         <file>images/kollada_animation.webp</file>
+        <file>images/kollada_noalpha.webp</file>
     </qresource>
 </RCC>