Stick PNGs on the clipboard on Wayland

Because using Qt's image data breaks transparency when copying between
canvases.

ChangeLog

@@ -15,6 +15,7 @@ Unreleased Version 2.2.2-pre
  * Server Fix: Don't pointlessly reload server certificates if they didn't change. Thanks Liz for reporting.
  * Server Fix: Work around too many authenticated users in a session, which could cause a crash. Thanks Liz for reporting.
  * Fix: Don't crash when filling with feathering and a canvas-filling selection. Thanks Meru for reporting.
+ * Fix: Work around broken transparency when copying images between canvases on Wayland. Thanks Absolute Goober for reporting.
 
 2024-11-06 Version 2.2.2-beta.4
  * Fix: Solve rendering glitches with selection outlines that happen on some systems. Thanks xxxx for reporting.

src/desktop/mainwindow.cpp

@@ -3593,11 +3593,13 @@ void MainWindow::copyText()
 		textedit->copy();
 }
 
+// clang-format on
 void MainWindow::paste()
 {
 	utils::ScopedOverrideCursor waitCursor;
 	const QMimeData *mimeData = Document::getClipboardData();
-	if(mimeData && mimeData->hasImage()) {
+	QImage img = Document::getClipboardImageData(mimeData);
+	if(!img.isNull()) {
 		QPoint pastepos;
 		bool pasteAtPos = false;
 
@@ -3611,25 +3613,27 @@ void MainWindow::paste()
 				qint64 pid = pos.at(2).toLongLong(&ok3);
 				qulonglong doc = pos.at(3).toULongLong(&ok4);
 				pasteAtPos = ok1 && ok2 && ok3 && ok4 &&
-					pid == qApp->applicationPid() && doc == m_doc->pasteId();
+							 pid == qApp->applicationPid() &&
+							 doc == m_doc->pasteId();
 			}
 		}
 
 		// Paste-in-place if we're the source (same process, same document)
-		if(pasteAtPos && m_canvasView->isPointVisible(pastepos))
-			pasteImage(mimeData->imageData().value<QImage>(), &pastepos, true);
-		else
-			pasteImage(mimeData->imageData().value<QImage>());
+		if(pasteAtPos && m_canvasView->isPointVisible(pastepos)) {
+			pasteImage(img, &pastepos, true);
+		} else {
+			pasteImage(img);
+		}
 	}
 }
 
-// clang-format on
 void MainWindow::pasteCentered()
 {
 	utils::ScopedOverrideCursor waitCursor;
 	const QMimeData *mimeData = Document::getClipboardData();
-	if(mimeData && mimeData->hasImage()) {
-		pasteImage(mimeData->imageData().value<QImage>(), nullptr, true);
+	QImage img = Document::getClipboardImageData(mimeData);
+	if(!img.isNull()) {
+		pasteImage(img, nullptr, true);
 	}
 }
 

src/libclient/document.cpp

@@ -1443,7 +1443,24 @@ bool Document::copyFromLayer(int layer)
 	if(!img.isNull() && layer == 0) {
 		fillBackground(img);
 	}
+
+#ifdef Q_OS_LINUX
+	// Copying image data from one Drawpile canvas to another is busted on
+	// Wayland, obliterating transparency. We store a PNG directly instead.
+	if(QGuiApplication::platformName() == QStringLiteral("wayland")) {
+		QByteArray bytes;
+		{
+			QBuffer buffer(&bytes);
+			buffer.open(QIODevice::WriteOnly);
+			img.save(&buffer, "PNG");
+		}
+		data->setData(QStringLiteral("image/png"), bytes);
+	} else {
+		data->setImageData(img);
+	}
+#else
 	data->setImageData(img);
+#endif
 
 	// Store also original coordinates
 	QRect bounds = m_canvas->selection()->bounds();
@@ -1684,6 +1701,22 @@ const QMimeData *Document::getClipboardData()
 #endif
 }
 
+QImage Document::getClipboardImageData(const QMimeData *mimeData)
+{
+	if(mimeData) {
+		if(mimeData->hasImage()) {
+			return mimeData->imageData().value<QImage>();
+		} else if(mimeData->hasFormat(QStringLiteral("image/png"))) {
+			QImage img;
+			if(img.loadFromData(
+				   mimeData->data(QStringLiteral("image/png")), "PNG")) {
+				return img;
+			}
+		}
+	}
+	return QImage();
+}
+
 #ifdef HAVE_CLIPBOARD_EMULATION
 QMimeData Document::clipboardData;
 #endif

src/libclient/document.h

@@ -302,6 +302,7 @@ public slots:
 	void addServerLogEntry(const QString &log);
 
 	static const QMimeData *getClipboardData();
+	static QImage getClipboardImageData(const QMimeData *mimeData);
 
 private slots:
 	void onServerLogin(