xcb: Fix bgr888 VNC sessions

Introduce a slow path for 24 and 32 bit BGR. We don't care about
performance here but it has to show the correct colors.

Task-number: QTBUG-42776
Change-Id: Ic73e8ca3950b2b956f06643165dcfac51e7540f3
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>

1 files changed, 32 insertions, 5 deletions

diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.cpp b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
index 5c9293c03d..06db4d83ac 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.cpp
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
@@ -303,13 +303,16 @@ QXcbBackingStore::~QXcbBackingStore()
 
 QPaintDevice *QXcbBackingStore::paintDevice()
 {
-    return m_image ? m_image->image() : 0;
+    if (!m_image)
+        return 0;
+    return m_rgbImage.isNull() ? m_image->image() : &m_rgbImage;
 }
 
 void QXcbBackingStore::beginPaint(const QRegion &region)
 {
     if (!m_image)
         return;
+
     int dpr = int(m_image->image()->devicePixelRatio());
     const int windowDpr = int(window()->devicePixelRatio());
     if (windowDpr != dpr) {
@@ -317,13 +320,13 @@ void QXcbBackingStore::beginPaint(const QRegion &region)
         dpr = int(m_image->image()->devicePixelRatio());
     }
 
-    QRegion xRegion =  dpr == 1 ? region : QTransform::fromScale(dpr,dpr).map(region);
-    m_image->preparePaint(xRegion);
+    m_paintRegion = dpr == 1 ? region : QTransform::fromScale(dpr,dpr).map(region);
+    m_image->preparePaint(m_paintRegion);
 
     if (m_image->image()->hasAlphaChannel()) {
-        QPainter p(m_image->image());
+        QPainter p(paintDevice());
         p.setCompositionMode(QPainter::CompositionMode_Source);
-        const QVector<QRect> rects = xRegion.rects();
+        const QVector<QRect> rects = m_paintRegion.rects();
         const QColor blank = Qt::transparent;
         for (QVector<QRect>::const_iterator it = rects.begin(); it != rects.end(); ++it) {
             p.fillRect(*it, blank);
@@ -331,6 +334,24 @@ void QXcbBackingStore::beginPaint(const QRegion &region)
     }
 }
 
+void QXcbBackingStore::endPaint()
+{
+    QXcbWindow *platformWindow = static_cast<QXcbWindow *>(window()->handle());
+    if (!platformWindow || !platformWindow->imageNeedsRgbSwap())
+        return;
+
+    // Slow path: the paint device was m_rgbImage. Now copy with swapping red
+    // and blue into m_image.
+    const QVector<QRect> rects = m_paintRegion.rects();
+    if (rects.isEmpty())
+        return;
+    QPainter p(m_image->image());
+    for (QVector<QRect>::const_iterator it = rects.begin(); it != rects.end(); ++it) {
+        const QRect rect = *it;
+        p.drawImage(rect.topLeft(), m_rgbImage.copy(rect).rgbSwapped());
+    }
+}
+
 #ifndef QT_NO_OPENGL
 QImage QXcbBackingStore::toImage() const
 {
@@ -426,6 +447,12 @@ void QXcbBackingStore::resize(const QSize &size, const QRegion &)
     delete m_image;
     m_image = new QXcbShmImage(screen, xSize, win->depth(), win->imageFormat());
     m_image->image()->setDevicePixelRatio(dpr);
+    // Slow path for bgr888 VNC: Create an additional image, paint into that and
+    // swap R and B while copying to m_image after each paint.
+    if (win->imageNeedsRgbSwap()) {
+        m_rgbImage = QImage(xSize, win->imageFormat());
+        m_rgbImage.setDevicePixelRatio(dpr);
+    }
     Q_XCB_NOOP(connection());
 }