QNX: always create buffers for child windows

The QNX raster backend worked on the assumption that child windows were
sharing their parent toplevel window buffer instead, and thus did not
have a buffer of their own. This piece of code dates back from the
BlackBerry days, and I am guessing the motivation was to tackle
mmrenderer/foreign windows.

In fact, not having buffers causes QWindow to malfunction, as
independent buffers are required.

This patch makes sure every QQnxWindow has a backing buffer, as
expected. Foreign widnows shall be dealt with via different means.

Change-Id: I059ac4f8ac684b3577048f874f82b866f21326b1
Reviewed-by: James McDonnell <jmcdonnell@blackberry.com>

2 files changed, 7 insertions, 21 deletions

diff --git a/src/plugins/platforms/qnx/qqnxrasterbackingstore.cpp b/src/plugins/platforms/qnx/qqnxrasterbackingstore.cpp
index fe68927fda..95b8fb26e3 100644
--- a/src/plugins/platforms/qnx/qqnxrasterbackingstore.cpp
+++ b/src/plugins/platforms/qnx/qqnxrasterbackingstore.cpp
@@ -89,17 +89,11 @@ void QQnxRasterBackingStore::flush(QWindow *window, const QRegion &region, const
     if (!m_needsPosting)
         return;
 
-    QQnxWindow *targetWindow = nullptr;
-    if (window)
-        targetWindow = static_cast<QQnxWindow *>(window->handle());
-
-    // we only need to flush the platformWindow backing store, since this is
-    // the buffer where all drawing operations of all windows, including the
-    // child windows, are performed; conceptually ,child windows have no buffers
-    // (actually they do have a 1x1 placeholder buffer due to libscreen limitations),
-    // since Qt will only draw to the backing store of the top-level window.
-    if (!targetWindow || targetWindow == platformWindow())
-        platformWindow()->post(region);  // update the display with newly rendered content
+    auto *targetWindow = window
+        ? static_cast<QQnxRasterWindow *>(window->handle()) : platformWindow();
+
+    if (targetWindow)
+        targetWindow->post(region);  // update the display with newly rendered content
 
     m_needsPosting = false;
     m_scrolled = false;
diff --git a/src/plugins/platforms/qnx/qqnxrasterwindow.cpp b/src/plugins/platforms/qnx/qqnxrasterwindow.cpp
index 0014ef8c6e..c91286217e 100644
--- a/src/plugins/platforms/qnx/qqnxrasterwindow.cpp
+++ b/src/plugins/platforms/qnx/qqnxrasterwindow.cpp
@@ -177,9 +177,8 @@ void QQnxRasterWindow::setParent(const QPlatformWindow *wnd)
 
 void QQnxRasterWindow::adjustBufferSize()
 {
-    // When having a raster window we don't need any buffers, since
-    // Qt will draw to the parent TLW backing store.
-    const QSize windowSize = window()->parent() ? QSize(0,0) : window()->size();
+    const QSize windowSize = window()->size();
+
     if (windowSize != bufferSize())
         setBufferSize(windowSize);
 }
@@ -195,13 +194,6 @@ void QQnxRasterWindow::resetBuffers()
     m_currentBufferIndex = -1;
     m_previousDirty = QRegion();
     m_scrolled = QRegion();
-    if (window()->parent() && bufferSize() == QSize(1,1)) {
-        // If we have a parent then we're not really rendering.  But if we don't render we'll
-        // be invisible and any children won't show up.  This should be harmless since we're
-        // rendering into a 1x1 window that has transparency set to discard.
-        renderBuffer();
-        post(QRegion(0,0,1,1));
-    }
 }
 
 void QQnxRasterWindow::blitPreviousToCurrent(const QRegion &region, int dx, int dy, bool flush)