Remove white backdrop from Krita thumbnails, preserve transparency

Thumbnails have an alpha channel, so there is no need to flatten the
image.

Also remove the scaling, its alreay done in the generic code.

thumbnail/CMakeLists.txt

@@ -221,7 +221,6 @@ add_library(kritathumbnail MODULE ${kritathumbnail_SRCS})
 target_link_libraries(kritathumbnail
     KF5::KIOWidgets
     KF5::Archive
-    Qt5::Gui
 )
 
 install(TARGETS kritathumbnail  DESTINATION ${KDE_INSTALL_PLUGINDIR})

thumbnail/kritacreator.cpp

@@ -22,7 +22,6 @@
 #include <kzip.h>
 
 // Qt
-#include <QPainter>
 #include <QImage>
 #include <QIODevice>
 #include <QFile>
@@ -54,7 +53,6 @@ bool KritaCreator::create(const QString &path, int width, int height, QImage &im
     }
 
     QImage thumbnail;
-    bool biggerSizeNeeded = true;
 
     // first check if normal thumbnail is good enough
     // ORA thumbnail?
@@ -69,35 +67,21 @@ bool KritaCreator::create(const QString &path, int width, int height, QImage &im
     }
 
     const KZipFileEntry* fileZipEntry = static_cast<const KZipFileEntry*>(entry);
-    bool thumbLoaded = thumbnail.loadFromData(fileZipEntry->data(), "PNG");
-    if (thumbLoaded) {
-        biggerSizeNeeded = (thumbnail.width() < width || thumbnail.height() < height);
-    }
-
-    if (biggerSizeNeeded || !thumbLoaded) {
-        entry = zip.directory()->entry(QLatin1String("mergedimage.png"));
+    bool thumbLoaded = image.loadFromData(fileZipEntry->data(), "PNG");
+    // The requested size is a boundingbox, so meeting one size is sufficient
+    if (thumbLoaded && ((image.width() >= width) || (image.height() >= height))) {
+        return true;
     }
 
+    entry = zip.directory()->entry(QLatin1String("mergedimage.png"));
     if (entry && entry->isFile()) {
         fileZipEntry = static_cast<const KZipFileEntry*>(entry);
         thumbLoaded = thumbnail.loadFromData(fileZipEntry->data(), "PNG");
         if (thumbLoaded) {
-            thumbnail = thumbnail.scaled(width, height, Qt::KeepAspectRatio, Qt::SmoothTransformation);
-        } else {
-            return false;
+            image = thumbnail;
+            return true;
         }
     }
 
-    if (!thumbnail.isNull()) {
-        // transparent areas put a white background behind the thumbnail
-        // (or better checkerboard?)
-        image = QImage(thumbnail.size(), QImage::Format_RGB32);
-        image.fill(QColor(Qt::white).rgb());
-        QPainter p(&image);
-        p.drawImage(QPoint(0, 0), thumbnail);
-
-        return true;
-    }
-
     return false;
 }