From 8359e44324a9554d1a340d91a0df962e83302228 Mon Sep 17 00:00:00 2001
From: Volker Hilsheimer <volker.hilsheimer@qt.io>
Date: Sat, 22 Jan 2022 00:43:56 +0100
Subject: [PATCH] Offscreen: Fix implementation of QScreen::grabWindow

If id == 0, then we should grab the specified rect from the screen.

To do that, find all windows intersecting with the screen geometry, and
compose their backing store images into a screen-size pixmap.

Otherwise, find the respective backing store and grab only that.

Remove the old code respecting the desktop widget, which is no longer a
thing in Qt 6. The code was also wrongly grabbing only the first
containing - not intersecting - window's backing store into the screen
pixmap.

Enable the QScreen::grabImage test for the offscreen platform, where it
now passes.

Task-number: QTBUG-99962
Change-Id: I16eca7b082d65095a62c73624f86a4423e997a7a
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
---
 .../platforms/offscreen/qoffscreencommon.cpp  | 28 +++++++++++--------
 tests/auto/gui/kernel/qscreen/tst_qscreen.cpp |  3 --
 2 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/src/plugins/platforms/offscreen/qoffscreencommon.cpp b/src/plugins/platforms/offscreen/qoffscreencommon.cpp
index f485b4eed8..76ebe79590 100644
--- a/src/plugins/platforms/offscreen/qoffscreencommon.cpp
+++ b/src/plugins/platforms/offscreen/qoffscreencommon.cpp
@@ -42,6 +42,7 @@
 #include "qoffscreenwindow.h"
 
 
+#include <QtGui/QPainter>
 #include <QtGui/private/qpixmap_raster_p.h>
 #include <QtGui/private/qguiapplication_p.h>
 
@@ -116,22 +117,25 @@ QPixmap QOffscreenScreen::grabWindow(WId id, int x, int y, int width, int height
 {
     QRect rect(x, y, width, height);
 
-    QOffscreenWindow *window = QOffscreenWindow::windowForWinId(id);
-    if (!window || window->window()->type() == Qt::Desktop) {
+    // id == 0 -> grab the screen, so all windows intersecting rect
+    if (!id) {
+        if (width == -1)
+            rect.setWidth(m_geometry.width());
+        if (height == -1)
+            rect.setHeight(m_geometry.height());
+        QPixmap screenImage(rect.size());
+        QPainter painter(&screenImage);
+        painter.translate(-x, -y);
         const QWindowList wl = QGuiApplication::topLevelWindows();
-        QWindow *containing = nullptr;
         for (QWindow *w : wl) {
-            if (w->type() != Qt::Desktop && w->isExposed() && w->geometry().contains(rect)) {
-                containing = w;
-                break;
+            if (w->isExposed() && w->geometry().intersects(rect)) {
+                QOffscreenBackingStore *store = QOffscreenBackingStore::backingStoreForWinId(w->winId());
+                const QImage windowImage = store ? store->toImage() : QImage();
+                if (!windowImage.isNull())
+                    painter.drawImage(w->position(), windowImage);
             }
         }
-
-        if (!containing)
-            return QPixmap();
-
-        id = containing->winId();
-        rect = rect.translated(-containing->geometry().topLeft());
+        return screenImage;
     }
 
     QOffscreenBackingStore *store = QOffscreenBackingStore::backingStoreForWinId(id);
diff --git a/tests/auto/gui/kernel/qscreen/tst_qscreen.cpp b/tests/auto/gui/kernel/qscreen/tst_qscreen.cpp
index 83d476e812..a6e9535e88 100644
--- a/tests/auto/gui/kernel/qscreen/tst_qscreen.cpp
+++ b/tests/auto/gui/kernel/qscreen/tst_qscreen.cpp
@@ -205,9 +205,6 @@ void tst_QScreen::orientationChange()
 
 void tst_QScreen::grabWindow_data()
 {
-    if (QGuiApplication::platformName().startsWith(QLatin1String("offscreen"), Qt::CaseInsensitive))
-        QSKIP("Offscreen: Screen grabbing not implemented.");
-
     QTest::addColumn<int>("screenIndex");
     QTest::addColumn<QByteArray>("screenName");
     QTest::addColumn<bool>("grabWindow");