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>

1 files changed, 13 insertions, 14 deletions

diff --git a/src/plugins/imageformats/webp/qwebphandler.cpp b/src/plugins/imageformats/webp/qwebphandler.cpp
index 3a7bf43..12c4001 100644
--- a/src/plugins/imageformats/webp/qwebphandler.cpp
+++ b/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
-    if (srcImage.format() != QImage::Format_ARGB32)
-        srcImage = srcImage.convertToFormat(QImage::Format_ARGB32);
-#else /* Q_BIG_ENDIAN */
-    if (srcImage.format() != QImage::Format_RGBA8888)
-        srcImage = srcImage.convertToFormat(QImage::Format_RGBA8888);
-#endif
+    bool alpha = srcImage.hasAlphaChannel();
+    QImage::Format newFormat = alpha ? QImage::Format_RGBA8888 : QImage::Format_RGB888;
+    if (srcImage.format() != newFormat)
+        srcImage = srcImage.convertToFormat(newFormat);
 
     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
-    if (!WebPPictureImportBGRA(&picture, srcImage.bits(), srcImage.bytesPerLine())) {
-#else /* Q_BIG_ENDIAN */
-    if (!WebPPictureImportRGBA(&picture, srcImage.bits(), srcImage.bytesPerLine())) {
-#endif
-        qWarning() << "failed to import image data to webp picture.";
+    bool failed = false;
+    if (alpha)
+        failed = !WebPPictureImportRGBA(&picture, srcImage.bits(), srcImage.bytesPerLine());
+    else
+        failed = !WebPPictureImportRGB(&picture, srcImage.bits(), srcImage.bytesPerLine());
 
+    if (failed) {
+        qWarning() << "failed to import image data to webp picture.";
         WebPPictureFree(&picture);
         return false;
     }