Let QPlatformBackingStore handle its own QOpenGLContext

The resources allocated by QPlatformBackingStore are owned by the class,
and should be allocated in a context the class also owns. This removes
the asymmetry of having to pass in a context to composeAndFlush, while
having to make the same context current before destroying the platform
backingstore.

The context owned by QPlatformBackingStore is shared with the associated
window though a new QWindowPrivate::shareContext() API.

The result is that on e.g. iOS, the backingstore does not need to tie
the resource allocation of QPlatformBackingStore to the global share
context, but can instead tie them to the per-window context, and hence
clean them up after each window is closed.

Task-number: QTBUG-56653
Change-Id: Ic1bcae50dafeeafaa8d16a7febd83b840ec6367a
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

4 files changed, 4 insertions, 20 deletions

diff --git a/src/plugins/platforms/ios/qiosbackingstore.h b/src/plugins/platforms/ios/qiosbackingstore.h
index 3954347471..e6b890251a 100644
--- a/src/plugins/platforms/ios/qiosbackingstore.h
+++ b/src/plugins/platforms/ios/qiosbackingstore.h
@@ -55,9 +55,6 @@ public:
     ~QIOSBackingStore();
 
     void flush(QWindow *window, const QRegion &region, const QPoint &offset) Q_DECL_OVERRIDE;
-
-private:
-    QOpenGLContext *m_context;
 };
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/ios/qiosbackingstore.mm b/src/plugins/platforms/ios/qiosbackingstore.mm
index 74229684e3..db4dd81b2e 100644
--- a/src/plugins/platforms/ios/qiosbackingstore.mm
+++ b/src/plugins/platforms/ios/qiosbackingstore.mm
@@ -55,7 +55,6 @@ QT_BEGIN_NAMESPACE
 */
 QIOSBackingStore::QIOSBackingStore(QWindow *window)
     : QRasterBackingStore(window)
-    , m_context(new QOpenGLContext)
 {
     // We use the surface both for raster operations and for GL drawing (when
     // we blit the raster image), so the type needs to cover both use cases.
@@ -64,22 +63,10 @@ QIOSBackingStore::QIOSBackingStore(QWindow *window)
 
     Q_ASSERT_X(window->surfaceType() != QSurface::OpenGLSurface, "QIOSBackingStore",
         "QBackingStore on iOS can only be used with raster-enabled surfaces.");
-
-    m_context->setFormat(window->requestedFormat());
-    m_context->setScreen(window->screen());
-    Q_ASSERT(QOpenGLContext::globalShareContext());
-    m_context->setShareContext(QOpenGLContext::globalShareContext());
-    m_context->create();
 }
 
 QIOSBackingStore::~QIOSBackingStore()
 {
-    // We're using composeAndFlush from QPlatformBackingStore, which
-    // need to clean up any textures in its destructor, so make the
-    // context current and keep it alive until QPlatformBackingStore
-    // has cleaned up everything.
-    m_context->makeCurrent(window());
-    m_context->deleteLater();
 }
 
 void QIOSBackingStore::flush(QWindow *window, const QRegion &region, const QPoint &offset)
@@ -98,7 +85,7 @@ void QIOSBackingStore::flush(QWindow *window, const QRegion &region, const QPoin
     }
 
     static QPlatformTextureList emptyTextureList;
-    composeAndFlush(window, region, offset, &emptyTextureList, m_context, false);
+    composeAndFlush(window, region, offset, &emptyTextureList, false);
 }
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.cpp b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
index 17927af3e3..420d1ac7c5 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.cpp
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
@@ -600,10 +600,10 @@ void QXcbBackingStore::flush(QWindow *window, const QRegion &region, const QPoin
 
 #ifndef QT_NO_OPENGL
 void QXcbBackingStore::composeAndFlush(QWindow *window, const QRegion &region, const QPoint &offset,
-                                       QPlatformTextureList *textures, QOpenGLContext *context,
+                                       QPlatformTextureList *textures,
                                        bool translucentBackground)
 {
-    QPlatformBackingStore::composeAndFlush(window, region, offset, textures, context, translucentBackground);
+    QPlatformBackingStore::composeAndFlush(window, region, offset, textures, translucentBackground);
 
     QXcbWindow *platformWindow = static_cast<QXcbWindow *>(window->handle());
     if (platformWindow->needsSync()) {
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.h b/src/plugins/platforms/xcb/qxcbbackingstore.h
index 94b5994004..2e8fbfb7fa 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.h
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.h
@@ -61,7 +61,7 @@ public:
     void flush(QWindow *window, const QRegion &region, const QPoint &offset) override;
 #ifndef QT_NO_OPENGL
     void composeAndFlush(QWindow *window, const QRegion &region, const QPoint &offset,
-                         QPlatformTextureList *textures, QOpenGLContext *context,
+                         QPlatformTextureList *textures,
                          bool translucentBackground) override;
 #endif
     QImage toImage() const override;