Scale window icon manually when getting from icon theme (#154)

Telegram/SourceFiles/window/main_window.cpp

@@ -141,11 +141,48 @@ QIcon CreateIcon(Main::Session *session) {
 	auto result = CreateOfficialIcon(session);
 
 #if defined Q_OS_UNIX && !defined Q_OS_MAC
-	if (
-		(!session || !session->supportMode())
-		&& cCustomAppIcon() == 0
-		&& !QFileInfo::exists(cWorkingDir() + "tdata/icon.png")) {
-		return QIcon::fromTheme(Platform::GetIconName(), result);
+	if ((session && session->supportMode())
+		|| (cCustomAppIcon() != 0)
+		|| QFileInfo::exists(cWorkingDir() + "tdata/icon.png")) {
+		return result;
+	}
+
+	const auto iconFromTheme = QIcon::fromTheme(
+		Platform::GetIconName(),
+		result);
+
+	result = QIcon();
+
+	static const auto iconSizes = {
+		16,
+		22,
+		32,
+		48,
+		64,
+		128,
+		256,
+	};
+
+	// Qt's standard QIconLoaderEngine sets availableSizes
+	// to XDG directories sizes, since svg icons are scalable,
+	// they could be only in one XDG folder (like 48x48)
+	// and Qt will set only a 48px icon to the window
+	// even though the icon could be scaled to other sizes.
+	// Thus, scale it manually to the most widespread sizes.
+	for (const auto iconSize : iconSizes) {
+		// We can't use QIcon::actualSize here
+		// since it works incorrectly with svg icon themes
+		const auto iconPixmap = iconFromTheme.pixmap(iconSize);
+
+		const auto iconPixmapSize = iconPixmap.size()
+			/ iconPixmap.devicePixelRatio();
+
+		// Not a svg icon, don't scale it
+		if (iconPixmapSize.width() != iconSize) {
+			return iconFromTheme;
+		}
+
+		result.addPixmap(iconPixmap);
 	}
 #endif