Consider the scale ratio when scaling down images

fixes #393

src/Utils.cpp

@@ -223,11 +223,41 @@ utils::scaleImageToPixmap(const QImage &img, int size)
                 return QPixmap();
 
         const double sz =
-          ceil(QApplication::desktop()->screen()->devicePixelRatioF() * (double)size);
+          std::ceil(QApplication::desktop()->screen()->devicePixelRatioF() * (double)size);
         return QPixmap::fromImage(
           img.scaled(sz, sz, Qt::IgnoreAspectRatio, Qt::SmoothTransformation));
 }
 
+QPixmap
+utils::scaleDown(uint64_t maxWidth, uint64_t maxHeight, const QPixmap &source)
+{
+        if (source.isNull())
+                return QPixmap();
+
+        const double pixelRatio = QApplication::desktop()->screen()->devicePixelRatioF();
+
+        // Take into account the scale factor of the screen.
+        maxWidth  = std::ceil(pixelRatio * (double)maxWidth);
+        maxHeight = std::ceil(pixelRatio * (double)maxHeight);
+
+        const double widthRatio     = (double)maxWidth / (double)source.width();
+        const double heightRatio    = (double)maxHeight / (double)source.height();
+        const double minAspectRatio = std::min(widthRatio, heightRatio);
+
+        // Size of the output image.
+        int w, h = 0;
+
+        if (minAspectRatio > 1) {
+                w = source.width();
+                h = source.height();
+        } else {
+                w = source.width() * minAspectRatio;
+                h = source.height() * minAspectRatio;
+        }
+
+        return source.scaled(w, h, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+}
+
 QString
 utils::mxcToHttp(const QUrl &url, const QString &server, int port)
 {

src/Utils.h

@@ -116,32 +116,8 @@ createDescriptionInfo(const Event &event, const QString &localUser, const QStrin
 }
 
 //! Scale down an image to fit to the given width & height limitations.
-template<class ImageType>
-ImageType
-scaleDown(uint64_t max_width, uint64_t max_height, const ImageType &source)
-{
-        if (source.isNull())
-                return QPixmap();
-
-        auto width_ratio  = (double)max_width / (double)source.width();
-        auto height_ratio = (double)max_height / (double)source.height();
-
-        auto min_aspect_ratio = std::min(width_ratio, height_ratio);
-
-        int final_width  = 0;
-        int final_height = 0;
-
-        if (min_aspect_ratio > 1) {
-                final_width  = source.width();
-                final_height = source.height();
-        } else {
-                final_width  = source.width() * min_aspect_ratio;
-                final_height = source.height() * min_aspect_ratio;
-        }
-
-        return source.scaled(
-          final_width, final_height, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
-}
+QPixmap
+scaleDown(uint64_t maxWidth, uint64_t maxHeight, const QPixmap &source);
 
 //! Delete items in a container based on a predicate.
 template<typename ContainerT, typename PredicateT>

src/dialogs/ImageOverlay.cpp

@@ -68,7 +68,7 @@ ImageOverlay::paintEvent(QPaintEvent *event)
         int max_width  = screen_.width() - 2 * outer_margin;
         int max_height = screen_.height();
 
-        image_ = utils::scaleDown<QPixmap>(max_width, max_height, originalImage_);
+        image_ = utils::scaleDown(max_width, max_height, originalImage_);
 
         int diff_x = max_width - image_.width();
         int diff_y = max_height - image_.height();

src/dialogs/PreviewUploadOverlay.cpp

@@ -108,7 +108,7 @@ PreviewUploadOverlay::init()
                 const auto maxHeight = winsize.height() * 0.8;
 
                 // Scale image preview to fit into the application window.
-                infoLabel_.setPixmap(utils::scaleDown<QPixmap>(maxWidth, maxHeight, image_));
+                infoLabel_.setPixmap(utils::scaleDown(maxWidth, maxHeight, image_));
                 move(center.x() - (width() * 0.5), center.y() - (height() * 0.5));
         } else {
                 infoLabel_.setAlignment(Qt::AlignLeft);

src/timeline/widgets/ImageItem.cpp

@@ -126,7 +126,7 @@ void
 ImageItem::setImage(const QPixmap &image)
 {
         image_        = image;
-        scaled_image_ = utils::scaleDown<QPixmap>(max_width_, max_height_, image_);
+        scaled_image_ = utils::scaleDown(max_width_, max_height_, image_);
 
         width_  = scaled_image_.width();
         height_ = scaled_image_.height();
@@ -165,7 +165,7 @@ ImageItem::resizeEvent(QResizeEvent *event)
         if (!image_)
                 return QWidget::resizeEvent(event);
 
-        scaled_image_ = utils::scaleDown<QPixmap>(max_width_, max_height_, image_);
+        scaled_image_ = utils::scaleDown(max_width_, max_height_, image_);
 
         width_  = scaled_image_.width();
         height_ = scaled_image_.height();