4 files changed, 43 insertions, 22 deletions

diff --git a/src/gui/opengl/qopenglpaintdevice.cpp b/src/gui/opengl/qopenglpaintdevice.cpp
index 6750458f83..96fc992b45 100644
--- a/src/gui/opengl/qopenglpaintdevice.cpp
+++ b/src/gui/opengl/qopenglpaintdevice.cpp
@@ -63,9 +63,9 @@ QT_BEGIN_NAMESPACE
 
     \ingroup painting-3D
 
-    The QOpenGLPaintDevice uses the current QOpenGL context to render
-    QPainter draw commands. It requires OpenGL (ES) 2.0 support or
-    higher.
+    The QOpenGLPaintDevice uses the \b current QOpenGL context to render
+    QPainter draw commands. The context is captured upon construction. It
+    requires support for OpenGL (ES) 2.0 or higher.
 
     \section1 Performance
 
@@ -359,9 +359,9 @@ bool QOpenGLPaintDevice::paintFlipped() const
 }
 
 /*!
-    This virtual method is provided as a callback to allow re-binding a
-    target frame buffer object when different QOpenGLPaintDevice instances
-    are issuing draw calls alternately on the same OpenGL context.
+    This virtual method is provided as a callback to allow re-binding a target
+    frame buffer object or context when different QOpenGLPaintDevice instances
+    are issuing draw calls alternately.
 
     QPainter::beginNativePainting will also trigger this method.
 */
diff --git a/src/gui/opengl/qopenglpaintengine.cpp b/src/gui/opengl/qopenglpaintengine.cpp
index de5b6be492..d0590ca521 100644
--- a/src/gui/opengl/qopenglpaintengine.cpp
+++ b/src/gui/opengl/qopenglpaintengine.cpp
@@ -1972,6 +1972,8 @@ bool QOpenGL2PaintEngineEx::begin(QPaintDevice *pdev)
     if (!d->device)
         return false;
 
+    d->device->ensureActiveTarget();
+
     if (d->device->context() != QOpenGLContext::currentContext()) {
         qWarning("QPainter::begin(): QOpenGLPaintDevice's context needs to be current");
         return false;
diff --git a/src/gui/painting/qplatformbackingstore.cpp b/src/gui/painting/qplatformbackingstore.cpp
index 3728b0bddd..e5b06f499c 100644
--- a/src/gui/painting/qplatformbackingstore.cpp
+++ b/src/gui/painting/qplatformbackingstore.cpp
@@ -90,6 +90,7 @@ struct QBackingstoreTextureInfo
 {
     GLuint textureId;
     QRect rect;
+    bool stacksOnTop;
 };
 
 Q_DECLARE_TYPEINFO(QBackingstoreTextureInfo, Q_MOVABLE_TYPE);
@@ -127,6 +128,12 @@ GLuint QPlatformTextureList::textureId(int index) const
     return d->textures.at(index).textureId;
 }
 
+bool QPlatformTextureList::stacksOnTop(int index) const
+{
+    Q_D(const QPlatformTextureList);
+    return d->textures.at(index).stacksOnTop;
+}
+
 QRect QPlatformTextureList::geometry(int index) const
 {
     Q_D(const QPlatformTextureList);
@@ -148,12 +155,13 @@ bool QPlatformTextureList::isLocked() const
     return d->locked;
 }
 
-void QPlatformTextureList::appendTexture(GLuint textureId, const QRect &geometry)
+void QPlatformTextureList::appendTexture(GLuint textureId, const QRect &geometry, bool stacksOnTop)
 {
     Q_D(QPlatformTextureList);
     QBackingstoreTextureInfo bi;
     bi.textureId = textureId;
     bi.rect = geometry;
+    bi.stacksOnTop = stacksOnTop;
     d->textures.append(bi);
 }
 
@@ -238,29 +246,39 @@ void QPlatformBackingStore::composeAndFlush(QWindow *window, const QRegion &regi
 
     QRect windowRect(QPoint(), window->size() * window->devicePixelRatio());
 
+    // Textures for renderToTexture widgets.
     for (int i = 0; i < textures->count(); ++i) {
-        GLuint textureId = textures->textureId(i);
-        funcs->glBindTexture(GL_TEXTURE_2D, textureId);
-
-        QRect targetRect = deviceRect(textures->geometry(i), window);
-        QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(targetRect, windowRect);
-        d_ptr->blitter->blit(textureId, target, QOpenGLTextureBlitter::OriginBottomLeft);
+        if (!textures->stacksOnTop(i)) {
+            QRect targetRect = deviceRect(textures->geometry(i), window);
+            QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(targetRect, windowRect);
+            d_ptr->blitter->blit(textures->textureId(i), target, QOpenGLTextureBlitter::OriginBottomLeft);
+        }
     }
 
-    GLuint textureId = toTexture(deviceRegion(region, window), &d_ptr->textureSize);
-    if (!textureId)
-        return;
-
     funcs->glEnable(GL_BLEND);
     funcs->glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 
-    QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(QRect(QPoint(), d_ptr->textureSize), windowRect);
-    d_ptr->blitter->setSwizzleRB(true);
-    d_ptr->blitter->blit(textureId, target, QOpenGLTextureBlitter::OriginTopLeft);
-    d_ptr->blitter->setSwizzleRB(false);
+    // Backingstore texture with the normal widgets.
+    GLuint textureId = toTexture(deviceRegion(region, window), &d_ptr->textureSize);
+    if (textureId) {
+        QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(QRect(QPoint(), d_ptr->textureSize), windowRect);
+        d_ptr->blitter->setSwizzleRB(true);
+        d_ptr->blitter->blit(textureId, target, QOpenGLTextureBlitter::OriginTopLeft);
+        d_ptr->blitter->setSwizzleRB(false);
+    }
+
+    // Textures for renderToTexture widgets that have WA_AlwaysStackOnTop set.
+    for (int i = 0; i < textures->count(); ++i) {
+        if (textures->stacksOnTop(i)) {
+            QRect targetRect = deviceRect(textures->geometry(i), window);
+            QMatrix4x4 target = QOpenGLTextureBlitter::targetTransform(targetRect, windowRect);
+            d_ptr->blitter->blit(textures->textureId(i), target, QOpenGLTextureBlitter::OriginBottomLeft);
+        }
+    }
 
     funcs->glDisable(GL_BLEND);
     d_ptr->blitter->release();
+
     context->swapBuffers(window);
 }
 
diff --git a/src/gui/painting/qplatformbackingstore.h b/src/gui/painting/qplatformbackingstore.h
index 4728622cac..fe0f460ed9 100644
--- a/src/gui/painting/qplatformbackingstore.h
+++ b/src/gui/painting/qplatformbackingstore.h
@@ -84,10 +84,11 @@ public:
     bool isEmpty() const { return count() == 0; }
     GLuint textureId(int index) const;
     QRect geometry(int index) const;
+    bool stacksOnTop(int index) const;
     void lock(bool on);
     bool isLocked() const;
 
-    void appendTexture(GLuint textureId, const QRect &geometry);
+    void appendTexture(GLuint textureId, const QRect &geometry, bool stacksOnTop = false);
     void clear();
 
  Q_SIGNALS: