Revive eglfs' raster window support

A number of consequences of the new rhi-based backingstore
composition were not handled. Most importantly, the fact
that RasterGLSurface is not a thing anymore in practice
causes challenges because we can no longer decide just
based on the surfaceType what a QWindow with OpenGLSurface
would be. (a plain GL window or a GL window with a backing
store?) Also, the backingstore needs to be able to initialize
its backing QRhi by itself, because with eglfs going through
OpenGL is the only way.

Amends 68a4c5da9a080101cccd8a3b2edb1c908da0ca8e

Fixes: QTBUG-102750
Change-Id: Ia1ca59d01e3012264a76b50e591612fdcc2a0bd6
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

3 files changed, 20 insertions, 11 deletions

diff --git a/src/plugins/platforms/eglfs/api/qeglfsscreen.cpp b/src/plugins/platforms/eglfs/api/qeglfsscreen.cpp
index 0b133c55a7..703259d66c 100644
--- a/src/plugins/platforms/eglfs/api/qeglfsscreen.cpp
+++ b/src/plugins/platforms/eglfs/api/qeglfsscreen.cpp
@@ -201,7 +201,8 @@ QPixmap QEglFSScreen::grabWindow(WId wid, int x, int y, int width, int height) c
 
     QImage img;
 
-    if (static_cast<QEglFSWindow *>(windows.first()->sourceWindow()->handle())->isRaster()) {
+    QEglFSWindow *primaryWin = static_cast<QEglFSWindow *>(windows.first()->sourceWindow()->handle());
+    if (primaryWin->isRaster() || primaryWin->backingStore()) {
         // Request the compositor to render everything into an FBO and read it back. This
         // is of course slow, but it's safe and reliable. It will not include the mouse
         // cursor, which is a plus.
diff --git a/src/plugins/platforms/eglfs/api/qeglfswindow.cpp b/src/plugins/platforms/eglfs/api/qeglfswindow.cpp
index 47f6d88e5c..13cc65bdaf 100644
--- a/src/plugins/platforms/eglfs/api/qeglfswindow.cpp
+++ b/src/plugins/platforms/eglfs/api/qeglfswindow.cpp
@@ -110,7 +110,7 @@ void QEglFSWindow::create()
 #ifndef QT_NO_OPENGL
     QOpenGLCompositor *compositor = QOpenGLCompositor::instance();
     if (screen->primarySurface() != EGL_NO_SURFACE) {
-        if (Q_UNLIKELY(!isRaster() || !compositor->targetWindow())) {
+        if (Q_UNLIKELY(isRaster() != (compositor->targetWindow() != nullptr))) {
 #  ifndef Q_OS_ANDROID
             // We can have either a single OpenGL window or multiple raster windows.
             // Other combinations cannot work.
@@ -137,21 +137,30 @@ void QEglFSWindow::create()
     screen->setPrimarySurface(m_surface);
 
 #ifndef QT_NO_OPENGL
-    if (isRaster()) {
+    compositor->setTargetWindow(window(), screen->rawGeometry());
+    compositor->setRotation(qEnvironmentVariableIntValue("QT_QPA_EGLFS_ROTATION"));
+#endif
+}
+
+void QEglFSWindow::setBackingStore(QOpenGLCompositorBackingStore *backingStore)
+{
+#ifndef QT_NO_OPENGL
+    if (!m_rasterCompositingContext) {
         m_rasterCompositingContext = new QOpenGLContext;
         m_rasterCompositingContext->setShareContext(qt_gl_global_share_context());
         m_rasterCompositingContext->setFormat(m_format);
         m_rasterCompositingContext->setScreen(window()->screen());
         if (Q_UNLIKELY(!m_rasterCompositingContext->create()))
             qFatal("EGLFS: Failed to create compositing context");
-        compositor->setTarget(m_rasterCompositingContext, window(), screen->rawGeometry());
-        compositor->setRotation(qEnvironmentVariableIntValue("QT_QPA_EGLFS_ROTATION"));
         // If there is a "root" window into which raster and QOpenGLWidget content is
         // composited, all other contexts must share with its context.
         if (!qt_gl_global_share_context())
             qt_gl_set_global_share_context(m_rasterCompositingContext);
     }
-#endif // QT_NO_OPENGL
+    QOpenGLCompositor *compositor = QOpenGLCompositor::instance();
+    compositor->setTargetContext(m_rasterCompositingContext);
+#endif
+    m_backingStore = backingStore;
 }
 
 void QEglFSWindow::destroy()
@@ -352,7 +361,7 @@ WId QEglFSWindow::winId() const
 
 void QEglFSWindow::setOpacity(qreal)
 {
-    if (!isRaster())
+    if (!isRaster() && !backingStore())
         qWarning("QEglFSWindow: Cannot set opacity for non-raster windows");
 
     // Nothing to do here. The opacity is stored in the QWindow.
diff --git a/src/plugins/platforms/eglfs/api/qeglfswindow_p.h b/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
index 6b34071d1a..1418ef82a1 100644
--- a/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
+++ b/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
@@ -103,12 +103,11 @@ public:
     void invalidateSurface() override;
     virtual void resetSurface();
 
-#ifndef QT_NO_OPENGL
-    QOpenGLCompositorBackingStore *backingStore() { return m_backingStore; }
-    void setBackingStore(QOpenGLCompositorBackingStore *backingStore) { m_backingStore = backingStore; }
-#endif
     bool isRaster() const;
+
 #ifndef QT_NO_OPENGL
+    QOpenGLCompositorBackingStore *backingStore() { return m_backingStore; }
+    void setBackingStore(QOpenGLCompositorBackingStore *backingStore);
     QWindow *sourceWindow() const override;
     const QPlatformTextureList *textures() const override;
     void endCompositing() override;