1 files changed, 29 insertions, 13 deletions

diff --git a/src/gui/painting/qplatformbackingstore.cpp b/src/gui/painting/qplatformbackingstore.cpp
index dd02e24676..5f873bfe7e 100644
--- a/src/gui/painting/qplatformbackingstore.cpp
+++ b/src/gui/painting/qplatformbackingstore.cpp
@@ -224,16 +224,16 @@ static inline QRect deviceRect(const QRect &rect, QWindow *window)
     return deviceRect;
 }
 
-static QRegion deviceRegion(const QRegion &region, QWindow *window)
+static QRegion deviceRegion(const QRegion &region, QWindow *window, const QPoint &offset)
 {
-    if (!(window->devicePixelRatio() > 1))
+    if (offset.isNull() && window->devicePixelRatio() <= 1)
         return region;
 
     QVector<QRect> rects;
     const QVector<QRect> regionRects = region.rects();
     rects.reserve(regionRects.count());
     foreach (const QRect &rect, regionRects)
-        rects.append(deviceRect(rect, window));
+        rects.append(deviceRect(rect.translated(offset), window));
 
     QRegion deviceRegion;
     deviceRegion.setRects(rects.constData(), rects.count());
@@ -246,10 +246,12 @@ static inline QRect toBottomLeftRect(const QRect &topLeftRect, int windowHeight)
                  topLeftRect.width(), topLeftRect.height());
 }
 
-static void blit(const QPlatformTextureList *textures, int idx, QWindow *window, const QRect &deviceWindowRect,
-                 QOpenGLTextureBlitter *blitter)
+static void blitTextureForWidget(const QPlatformTextureList *textures, int idx, QWindow *window, const QRect &deviceWindowRect,
+                                 QOpenGLTextureBlitter *blitter, const QPoint &offset)
 {
-    const QRect rectInWindow = textures->geometry(idx);
+    QRect rectInWindow = textures->geometry(idx);
+    // relative to the TLW, not necessarily our window (if the flush is for a native child widget), have to adjust
+    rectInWindow.translate(-offset);
     QRect clipRect = textures->clipRect(idx);
     if (clipRect.isEmpty())
         clipRect = QRect(QPoint(0, 0), rectInWindow.size());
@@ -274,7 +276,9 @@ static void blit(const QPlatformTextureList *textures, int idx, QWindow *window,
     and composes using OpenGL. May be reimplemented in subclasses if there
     is a more efficient native way to do it.
 
-    Note that the \a offset parameter is currently unused.
+    \note \a region is relative to the window which may not be top-level in case
+    \a window corresponds to a native child widget. \a offset is the position of
+    the native child relative to the top-level window.
  */
 
 void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &region,
@@ -282,7 +286,8 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
                                             QPlatformTextureList *textures, QOpenGLContext *context,
                                             bool translucentBackground)
 {
-    Q_UNUSED(offset);
+    if (!qt_window_private(window)->receivedExpose)
+        return;
 
     if (!context->makeCurrent(window)) {
         qWarning("composeAndFlush: makeCurrent() failed");
@@ -306,7 +311,7 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
     // Textures for renderToTexture widgets.
     for (int i = 0; i < textures->count(); ++i) {
         if (!textures->flags(i).testFlag(QPlatformTextureList::StacksOnTop))
-            blit(textures, i, window, deviceWindowRect, d_ptr->blitter);
+            blitTextureForWidget(textures, i, window, deviceWindowRect, d_ptr->blitter, offset);
     }
 
     funcs->glEnable(GL_BLEND);
@@ -348,17 +353,26 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
         textureId = d_ptr->textureId;
     } else {
         TextureFlags flags = 0;
-        textureId = toTexture(deviceRegion(region, window), &d_ptr->textureSize, &flags);
+        textureId = toTexture(deviceRegion(region, window, offset), &d_ptr->textureSize, &flags);
         d_ptr->needsSwizzle = (flags & TextureSwizzle) != 0;
         if (flags & TextureFlip)
             origin = QOpenGLTextureBlitter::OriginBottomLeft;
     }
 
     if (textureId) {
-        QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(QRect(QPoint(), d_ptr->textureSize), deviceWindowRect);
         if (d_ptr->needsSwizzle)
             d_ptr->blitter->setSwizzleRB(true);
-        d_ptr->blitter->blit(textureId, target, origin);
+        // offset is usually (0, 0) unless we have native child widgets.
+        if (offset.isNull()) {
+            d_ptr->blitter->blit(textureId, QMatrix4x4(), origin);
+        } else {
+            // The backingstore is for the entire tlw. offset tells the position of the native child in the tlw.
+            const QRect srcRect = toBottomLeftRect(deviceWindowRect.translated(offset), d_ptr->textureSize.height());
+            const QMatrix3x3 source = QOpenGLTextureBlitter::sourceTransform(deviceRect(srcRect, window),
+                                                                             d_ptr->textureSize,
+                                                                             origin);
+            d_ptr->blitter->blit(textureId, QMatrix4x4(), source);
+        }
         if (d_ptr->needsSwizzle)
             d_ptr->blitter->setSwizzleRB(false);
     }
@@ -366,7 +380,7 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
     // Textures for renderToTexture widgets that have WA_AlwaysStackOnTop set.
     for (int i = 0; i < textures->count(); ++i) {
         if (textures->flags(i).testFlag(QPlatformTextureList::StacksOnTop))
-            blit(textures, i, window, deviceWindowRect, d_ptr->blitter);
+            blitTextureForWidget(textures, i, window, deviceWindowRect, d_ptr->blitter, offset);
     }
 
     funcs->glDisable(GL_BLEND);
@@ -413,6 +427,8 @@ QImage QPlatformBackingStore::toImage() const
 
   If the image has to be flipped (e.g. because the texture is attached to an FBO), \a
   flags will be set to include \c TextureFlip.
+
+  \note \a dirtyRegion is relative to the backingstore so no adjustment is needed.
  */
 GLuint QPlatformBackingStore::toTexture(const QRegion &dirtyRegion, QSize *textureSize, TextureFlags *flags) const
 {