Support alpha in QQuickWindow::grabWindow().

Change-Id: I2dd69745427d8f5e882303d2a4de3935ddca02e9
Task-number: QTBUG-48787
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>

5 files changed, 31 insertions, 10 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index c8256ed62a..6542bde4f1 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -3306,7 +3306,8 @@ QImage QQuickWindow::grabWindow()
         d->syncSceneGraph();
         d->renderSceneGraph(size());
 
-        QImage image = qt_gl_read_framebuffer(size() * effectiveDevicePixelRatio(), false, false);
+        bool alpha = format().alphaBufferSize() > 0 && color().alpha() < 255;
+        QImage image = qt_gl_read_framebuffer(size() * effectiveDevicePixelRatio(), alpha, alpha);
         d->cleanupNodesOnShutdown();
         d->context->invalidate();
         context.doneCurrent();
diff --git a/src/quick/scenegraph/qsgrenderloop.cpp b/src/quick/scenegraph/qsgrenderloop.cpp
index 3059b750f2..87dd521807 100644
--- a/src/quick/scenegraph/qsgrenderloop.cpp
+++ b/src/quick/scenegraph/qsgrenderloop.cpp
@@ -398,7 +398,8 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
     Q_QUICK_SG_PROFILE_RECORD(QQuickProfiler::SceneGraphRenderLoopFrame);
 
     if (data.grabOnly) {
-        grabContent = qt_gl_read_framebuffer(window->size() * window->effectiveDevicePixelRatio(), false, false);
+        bool alpha = window->format().alphaBufferSize() > 0 && window->color().alpha() != 255;
+        grabContent = qt_gl_read_framebuffer(window->size() * window->effectiveDevicePixelRatio(), alpha, alpha);
         data.grabOnly = false;
     }
 
diff --git a/src/quick/scenegraph/qsgthreadedrenderloop.cpp b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
index 4b78fefa99..8d6bea9e67 100644
--- a/src/quick/scenegraph/qsgthreadedrenderloop.cpp
+++ b/src/quick/scenegraph/qsgthreadedrenderloop.cpp
@@ -421,7 +421,8 @@ bool QSGRenderThread::event(QEvent *e)
             QQuickWindowPrivate::get(ce->window)->renderSceneGraph(ce->window->size());
 
             qCDebug(QSG_LOG_RENDERLOOP) << QSG_RT_PAD << "- grabbing result";
-            *ce->image = qt_gl_read_framebuffer(windowSize * ce->window->effectiveDevicePixelRatio(), false, false);
+            bool alpha = ce->window->format().alphaBufferSize() > 0 && ce->window->color().alpha() != 255;
+            *ce->image = qt_gl_read_framebuffer(windowSize * ce->window->effectiveDevicePixelRatio(), alpha, alpha);
         }
         qCDebug(QSG_LOG_RENDERLOOP) << QSG_RT_PAD << "- waking gui to handle result";
         waitCondition.wakeOne();
diff --git a/src/quick/scenegraph/qsgwindowsrenderloop.cpp b/src/quick/scenegraph/qsgwindowsrenderloop.cpp
index 7fd9651618..04a46bf929 100644
--- a/src/quick/scenegraph/qsgwindowsrenderloop.cpp
+++ b/src/quick/scenegraph/qsgwindowsrenderloop.cpp
@@ -312,7 +312,8 @@ QImage QSGWindowsRenderLoop::grab(QQuickWindow *window)
     d->syncSceneGraph();
     d->renderSceneGraph(window->size());
 
-    QImage image = qt_gl_read_framebuffer(window->size() * window->effectiveDevicePixelRatio(), false, false);
+    bool alpha = window->format().alphaBufferSize() > 0 && window->color().alpha() != 255;
+    QImage image = qt_gl_read_framebuffer(window->size() * window->effectiveDevicePixelRatio(), alpha, alpha);
     return image;
 }
 
diff --git a/tests/auto/quick/qquickwindow/tst_qquickwindow.cpp b/tests/auto/quick/qquickwindow/tst_qquickwindow.cpp
index e1ea068a62..f53ade9541 100644
--- a/tests/auto/quick/qquickwindow/tst_qquickwindow.cpp
+++ b/tests/auto/quick/qquickwindow/tst_qquickwindow.cpp
@@ -277,6 +277,10 @@ class tst_qquickwindow : public QQmlDataTest
 {
     Q_OBJECT
 public:
+    tst_qquickwindow()
+    {
+        QQuickWindow::setDefaultAlphaBuffer(true);
+    }
 
 private slots:
     void initTestCase()
@@ -1081,17 +1085,25 @@ void tst_qquickwindow::defaultState()
 void tst_qquickwindow::grab_data()
 {
     QTest::addColumn<bool>("visible");
-    QTest::newRow("visible") << true;
-    QTest::newRow("invisible") << false;
+    QTest::addColumn<bool>("alpha");
+    QTest::newRow("visible,opaque") << true << false;
+    QTest::newRow("invisible,opaque") << false << false;
+    QTest::newRow("visible,transparent") << true << true;
+    QTest::newRow("invisible,transparent") << false << true;
 }
 
 void tst_qquickwindow::grab()
 {
     QFETCH(bool, visible);
+    QFETCH(bool, alpha);
 
     QQuickWindow window;
     window.setTitle(QLatin1String(QTest::currentTestFunction()) + QLatin1Char(' ') + QLatin1String(QTest::currentDataTag()));
-    window.setColor(Qt::red);
+    if (alpha) {
+        window.setColor(QColor(0, 0, 0, 0));
+    } else {
+        window.setColor(Qt::red);
+    }
 
     window.resize(250, 250);
 
@@ -1103,9 +1115,14 @@ void tst_qquickwindow::grab()
     }
 
     QImage content = window.grabWindow();
-    QCOMPARE(content.width(), window.width());
-    QCOMPARE(content.height(), window.height());
-    QCOMPARE((uint) content.convertToFormat(QImage::Format_RGB32).pixel(0, 0), (uint) 0xffff0000);
+    QCOMPARE(content.width(), int(window.width() * window.devicePixelRatio()));
+    QCOMPARE(content.height(), int(window.height() * window.devicePixelRatio()));
+
+    if (alpha) {
+        QCOMPARE((uint) content.convertToFormat(QImage::Format_ARGB32_Premultiplied).pixel(0, 0), (uint) 0x00000000);
+    } else {
+        QCOMPARE((uint) content.convertToFormat(QImage::Format_RGB32).pixel(0, 0), (uint) 0xffff0000);
+    }
 }
 
 void tst_qquickwindow::multipleWindows()