Issue #247 - [GTK][Wayland] Drag&drop gets stuck

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Control.java

@@ -113,7 +113,6 @@ public abstract class Control extends Widget implements Drawable {
 	 * is currently pressed or released for DND.
 	 */
 	static boolean mouseDown;
-	boolean dragBegun;
 
 	/**
 	 * Flag to check the scale factor upon the first drawing of this Control.
@@ -2671,36 +2670,36 @@ boolean dragDetect (int button, int count, int stateMask, int x, int y) {
 }
 
 boolean dragDetect (int x, int y, boolean filter, boolean dragOnTimeout, boolean [] consume) {
-	boolean dragging = false;
 	/*
 	 * Feature in GTK: In order to support both X.11/Wayland, GTKGestures are used
 	 *  as of GTK3.14 in order to acquire mouse position offsets to decide on dragging.
 	 *  See Bug 503431.
 	 */
 	if (!OS.isX11()) { // Wayland
+		// Don't drag if mouse is not down. This condition is not as
+		// trivial as it seems, see Bug 541635 where drag is tested
+		// after drag already completed and mouse is released.
+		if (!mouseDown) {
+			return false;
+		}
+
 		double [] offsetX = new double[1];
 		double [] offsetY = new double [1];
 		double [] startX = new double[1];
 		double [] startY = new double [1];
-		if (GTK.gtk_gesture_drag_get_start_point(dragGesture, startX, startY)) {
-			GTK.gtk_gesture_drag_get_offset(dragGesture, offsetX, offsetY);
-			if (GTK3.gtk_drag_check_threshold(handle, (int)startX[0], (int) startY[0], (int) startX[0]
-					+ (int) offsetX[0], (int) startY[0] + (int) offsetY[0])) {
-				dragging = true;
-			}
-		} else {
+		if (!GTK.gtk_gesture_drag_get_start_point(dragGesture, startX, startY)) {
 			return false;
 		}
-		// Block until mouse was released or drag was detected, see Bug 515396.
-		while (true) {
-			if (!mouseDown) {
-				return false;
-			}
-			if (dragBegun) {
-				return true;
-			}
+
+		GTK.gtk_gesture_drag_get_offset(dragGesture, offsetX, offsetY);
+		if (GTK3.gtk_drag_check_threshold(handle, (int)startX[0], (int) startY[0], (int) startX[0]
+				+ (int) offsetX[0], (int) startY[0] + (int) offsetY[0])) {
+			return true;
 		}
+
+		return false;
 	} else {
+		boolean dragging = false;
 		boolean quit = false;
 		//428852 DND workaround for GTK3.
 		//Gtk3 no longer sends motion events on the same control during thread sleep
@@ -2801,8 +2800,8 @@ boolean dragDetect (int x, int y, boolean filter, boolean dragOnTimeout, boolean
 			}
 			gdk_event_free (eventPtr);
 		}
+		return dragging;
 	}
-	return dragging;
 }
 
 boolean filterKey (long event) {
@@ -3429,7 +3428,6 @@ void gtk_style_context_get_border (long context, int state, GtkBorder padding) {
 @Override
 void gtk_gesture_press_event (long gesture, int n_press, double x, double y, long event) {
 	mouseDown = true;
-	dragBegun = false;
 
 	int eventButton = GDK.gdk_button_event_get_button(event);
 	int eventTime = GDK.gdk_event_get_time(event);
@@ -3473,7 +3471,6 @@ long gtk_button_press_event (long widget, long event) {
 
 long gtk_button_press_event (long widget, long event, boolean sendMouseDown) {
 	mouseDown = true;
-	dragBegun = false;
 
 	double [] eventX = new double [1];
 	double [] eventY = new double [1];
@@ -4109,10 +4106,6 @@ long gtk_mnemonic_activate (long widget, long arg1) {
 
 @Override
 void gtk4_motion_event(long controller, double x, double y, long event) {
-	if (mouseDown) {
-		dragBegun = true;
-	}
-
 	if (this == display.currentControl && (hooks(SWT.MouseHover) || filters(SWT.MouseHover))) {
 		display.addMouseHoverTimeout(handle);
 	}
@@ -4143,9 +4136,6 @@ void gtk4_motion_event(long controller, double x, double y, long event) {
 @Override
 long gtk_motion_notify_event (long widget, long event) {
 	int result;
-	if (mouseDown) {
-		dragBegun = true;
-	}
 
 	double[] eventX = new double[1];
 	double[] eventY = new double[1];

tests/org.eclipse.swt.tests/ManualTests/org/eclipse/swt/tests/manual/Issue0247_WaylandDragDropGetsStuck.java

@@ -0,0 +1,80 @@
+/*******************************************************************************
+ * Copyright (c) 2022 Syntevo and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Syntevo - initial API and implementation
+ *******************************************************************************/
+
+package org.eclipse.swt.tests.manual;
+
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.dnd.*;
+import org.eclipse.swt.layout.*;
+import org.eclipse.swt.widgets.*;
+
+public class Issue0247_WaylandDragDropGetsStuck {
+	public static void main(String[] args) {
+		final Display display = new Display ();
+
+		final Shell shell = new Shell (display);
+		shell.setLayout (new GridLayout (1, true));
+
+		Label hint = new Label (shell, 0);
+		hint.setText (
+			"1) Use Linux with Wayland\n" +
+			"2) Drag TreeItem\n" +
+			"3) Issue 0247: Dragging begins immediately when mouse is moved without any move threshold\n" +
+			"4) Move mouse over TreeItem slowly and double-click once in a while\n" +
+			"5) Issue 0247: Sometimes, counter will grow, indicating that there's an unfinished drag.\n" +
+			"   You will also see it by DRAGGING indicator being stuck.\n"
+		);
+
+		Tree control = new Tree (shell, SWT.BORDER);
+		for (int i = 0; i < 5; i++) {
+			new TreeItem(control, 0).setText("TreeItem #" + i);
+		}
+
+		Label labelIsDrag = new Label(shell, 0);
+		labelIsDrag.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
+
+		final int[] numActiveDrags = new int[1];
+		DragSource dragSource = new DragSource (control, DND.DROP_MOVE | DND.DROP_COPY);
+		dragSource.setTransfer (TextTransfer.getInstance ());
+		dragSource.addDragListener (new DragSourceListener() {
+			@Override
+			public void dragStart(DragSourceEvent event) {
+				labelIsDrag.setText("DRAGGING");
+				numActiveDrags[0]++;
+			}
+
+			@Override
+			public void dragSetData(DragSourceEvent event) {
+				event.data = "Data";
+			}
+
+			@Override
+			public void dragFinished(DragSourceEvent event) {
+				numActiveDrags[0]--;
+				labelIsDrag.setText("" + numActiveDrags[0]);
+			}
+		});
+
+		shell.pack ();
+		shell.open ();
+
+		while (!shell.isDisposed ()) {
+			if (!display.readAndDispatch ()) {
+				display.sleep ();
+			}
+		}
+
+		display.dispose ();
+	}
+}