[Gtk4] Fix PaintListener paint ordering for all widget types

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

@@ -558,6 +558,18 @@ void snapshotBackground (long handle, long snapshot) {
 	Graphene.graphene_rect_free(rect);
 }
 
+@Override
+void snapshotToDraw (long handle, long snapshot) {
+	// Containers paint before children so SWT.Paint backgrounds appear behind child controls,
+	// matching GTK3 EXPOSE_EVENT_INVERSE (after=false) behavior.
+	snapshotPaint(handle, snapshot);
+}
+
+@Override
+void snapshotToDrawAfterChildren (long handle, long snapshot) {
+	// Suppress Control's after-children paint: Composite already painted before children above.
+}
+
 
 /**
  * Fills the interior of the rectangle specified by the arguments,

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

@@ -524,6 +524,25 @@ boolean hooksPaint () {
 	return hooks (SWT.Paint) || filters (SWT.Paint);
 }
 
+@Override
+void snapshotPaint (long handle, long snapshot) {
+	/*
+	 * Guard against creating an empty Cairo render node when there are no paint
+	 * listeners. gtk_snapshot_append_cairo() appends a node immediately; leaving it
+	 * empty/unfinished causes it to obscure render nodes already in the snapshot
+	 * (e.g. GtkTreeView content snapshotted before this call).
+	 */
+	if (!hooksPaint()) return;
+	super.snapshotPaint(handle, snapshot);
+}
+
+@Override
+void snapshotToDrawAfterChildren (long handle, long snapshot) {
+	// Leaf controls (Button, Label, etc.) paint after children so SWT.Paint listeners
+	// draw on top of the native widget appearance, matching GTK3 DRAW (after=true) behavior.
+	snapshotPaint(handle, snapshot);
+}
+
 @Override
 long hoverProc (long widget) {
 	int[] x = new int[1], y = new int[1], mask = new int[1];

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

@@ -1720,7 +1720,7 @@ void snapshotDrawProc(long handle, long snapshot) {
 	// Draw background before children so it appears behind them
 	if (widget != null) widget.snapshotBackground(handle, snapshot);
 
-	// Draw SWT custom paint before children so child widgets remain visible.
+	// Paint before children (used by Composite subclasses for backgrounds)
 	if (widget != null) widget.snapshotToDraw(handle, snapshot);
 
 	long child = GTK4.gtk_widget_get_first_child(handle);
@@ -1729,6 +1729,9 @@ void snapshotDrawProc(long handle, long snapshot) {
 		GTK4.gtk_widget_snapshot_child(handle, child, snapshot);
 		child = GTK4.gtk_widget_get_next_sibling(child);
 	}
+
+	// Paint after children (used by leaf controls for overlay/on-top drawing)
+	if (widget != null) widget.snapshotToDrawAfterChildren(handle, snapshot);
 }
 
 static long rendererGetPreferredWidthProc (long cell, long handle, long minimun_size, long natural_size) {

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

@@ -4233,6 +4233,18 @@ private void gtk3_paintEvent(long cairo) {
 	event.gc = null;
 }
 
+@Override
+void snapshotToDraw(long handle, long snapshot) {
+	// Table renders via native GTK children (GtkScrolledWindow > GtkTreeView).
+	// Like GTK3 where Table explicitly fires paint in EXPOSE_EVENT (after=true),
+	// GTK4 must paint after children so SWT.Paint overlays appear on top.
+}
+
+@Override
+void snapshotToDrawAfterChildren(long handle, long snapshot) {
+	snapshotPaint(handle, snapshot);
+}
+
 @Override
 public void dispose() {
 	super.dispose();

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

@@ -4306,6 +4306,18 @@ private void gtk3_paintEvent(long cairo) {
 	event.gc = null;
 }
 
+@Override
+void snapshotToDraw(long handle, long snapshot) {
+	// Tree renders via native GTK children (GtkScrolledWindow > GtkTreeView).
+	// Like GTK3 where Tree explicitly fires paint in EXPOSE_EVENT (after=true),
+	// GTK4 must paint after children so SWT.Paint overlays appear on top.
+}
+
+@Override
+void snapshotToDrawAfterChildren(long handle, long snapshot) {
+	snapshotPaint(handle, snapshot);
+}
+
 private void throwCannotRemoveItem(int i) {
 	String message = "Cannot remove item with index " + i + ".";
 	throw new SWTException(message);

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

@@ -2292,12 +2292,10 @@ void snapshotBackground (long handle, long snapshot) {
 
 /**
  * Converts an incoming snapshot into a gtk_draw() call, complete with
- * a Cairo context.
- *
- * @param handle the widget receiving the snapshot
- * @param snapshot the actual GtkSnapshot
+ * a Cairo context. Used by subclasses to
+ * trigger painting at the appropriate point in the snapshot order.
  */
-void snapshotToDraw (long handle, long snapshot) {
+void snapshotPaint (long handle, long snapshot) {
 	GtkAllocation allocation = new GtkAllocation();
 	GTK.gtk_widget_get_allocation(handle, allocation);
 	long rect = Graphene.graphene_rect_alloc();
@@ -2312,6 +2310,20 @@ void snapshotToDraw (long handle, long snapshot) {
 	Graphene.graphene_rect_free(rect);
 }
 
+/**
+ * Called before child widgets are snapshotted. Containers (Composite) override
+ * this to paint backgrounds behind their children.
+ */
+void snapshotToDraw (long handle, long snapshot) {
+}
+
+/**
+ * Called after child widgets are snapshotted. Leaf controls (Button, Label,
+ * etc.) override this to paint on top of their native appearance.
+ */
+void snapshotToDrawAfterChildren (long handle, long snapshot) {
+}
+
 long gtk_widget_get_window (long widget){
 	GTK.gtk_widget_realize(widget);
 	return GTK3.gtk_widget_get_window (widget);