Add support for grabWindow() on eglfs with widgets

For real OpenGL content it is still not supported because we have no reliable way
to read back the contents at arbitrary times. Applications should rather use
QQuickWindow::grabWindow() in that case.

[ChangeLog][QtGui] Support for QScreen::grabWindow() is now available on
embedded platforms (eglfs, linuxfb).

Task-number: QTBUG-44937
Change-Id: I4ad046062782c160f5bb9f8f2a2fe82f2e7394cc
Reviewed-by: Andy Nichols <andy.nichols@theqtcompany.com>

2 files changed, 27 insertions, 4 deletions

diff --git a/src/platformsupport/platformcompositor/qopenglcompositor.cpp b/src/platformsupport/platformcompositor/qopenglcompositor.cpp
index 3048b2b777..3fd6c999a2 100644
--- a/src/platformsupport/platformcompositor/qopenglcompositor.cpp
+++ b/src/platformsupport/platformcompositor/qopenglcompositor.cpp
@@ -32,6 +32,7 @@
 ****************************************************************************/
 
 #include <QtGui/QOpenGLContext>
+#include <QtGui/QOpenGLFramebufferObject>
 #include <QtGui/QWindow>
 #include <QtGui/QMatrix4x4>
 #include <qpa/qplatformbackingstore.h>
@@ -76,7 +77,7 @@ QOpenGLCompositor::QOpenGLCompositor()
     Q_ASSERT(!compositor);
     m_updateTimer.setSingleShot(true);
     m_updateTimer.setInterval(0);
-    connect(&m_updateTimer, SIGNAL(timeout()), SLOT(renderAll()));
+    connect(&m_updateTimer, SIGNAL(timeout()), SLOT(handleRenderAllRequest()));
 }
 
 QOpenGLCompositor::~QOpenGLCompositor()
@@ -98,10 +99,26 @@ void QOpenGLCompositor::update()
         m_updateTimer.start();
 }
 
-void QOpenGLCompositor::renderAll()
+QImage QOpenGLCompositor::grab()
 {
     Q_ASSERT(m_context && m_targetWindow);
     m_context->makeCurrent(m_targetWindow);
+    QScopedPointer<QOpenGLFramebufferObject> fbo(new QOpenGLFramebufferObject(m_targetWindow->geometry().size()));
+    renderAll(fbo.data());
+    return fbo->toImage();
+}
+
+void QOpenGLCompositor::handleRenderAllRequest()
+{
+    Q_ASSERT(m_context && m_targetWindow);
+    m_context->makeCurrent(m_targetWindow);
+    renderAll(0);
+}
+
+void QOpenGLCompositor::renderAll(QOpenGLFramebufferObject *fbo)
+{
+    if (fbo)
+        fbo->bind();
 
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
 
@@ -120,7 +137,10 @@ void QOpenGLCompositor::renderAll()
         render(m_windows.at(i));
 
     m_blitter.release();
-    m_context->swapBuffers(m_targetWindow);
+    if (!fbo)
+        m_context->swapBuffers(m_targetWindow);
+    else
+        fbo->release();
 
     for (int i = 0; i < m_windows.size(); ++i)
         m_windows.at(i)->endCompositing();
diff --git a/src/platformsupport/platformcompositor/qopenglcompositor_p.h b/src/platformsupport/platformcompositor/qopenglcompositor_p.h
index 257bbf2531..2a8257305b 100644
--- a/src/platformsupport/platformcompositor/qopenglcompositor_p.h
+++ b/src/platformsupport/platformcompositor/qopenglcompositor_p.h
@@ -51,6 +51,7 @@
 QT_BEGIN_NAMESPACE
 
 class QOpenGLContext;
+class QOpenGLFramebufferObject;
 class QWindow;
 class QPlatformTextureList;
 
@@ -76,6 +77,7 @@ public:
     QWindow *targetWindow() const { return m_targetWindow; }
 
     void update();
+    QImage grab();
 
     QList<QOpenGLCompositorWindow *> windows() const { return m_windows; }
     void addWindow(QOpenGLCompositorWindow *window);
@@ -87,12 +89,13 @@ signals:
     void topWindowChanged(QOpenGLCompositorWindow *window);
 
 private slots:
-    void renderAll();
+    void handleRenderAllRequest();
 
 private:
     QOpenGLCompositor();
     ~QOpenGLCompositor();
 
+    void renderAll(QOpenGLFramebufferObject *fbo);
     void render(QOpenGLCompositorWindow *window);
 
     QOpenGLContext *m_context;