Register QPlatformBackingStoreOpenGLSupport when needed

Static builds can not rely on a constructor function in the QtOpenGL
library, as that will be linked out unless something in the application
pulls it in.

Instead we export a helper function that clients that depend on
OpenGL support in QPlatformBackingStore can use to bring it it.

Change-Id: Ic54058bf413a476287884c78df5624b862f97695
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

2 files changed, 8 insertions, 9 deletions

diff --git a/src/opengl/qplatformbackingstoreopenglsupport.cpp b/src/opengl/qplatformbackingstoreopenglsupport.cpp
index 6f893671c0..46e36c23d4 100644
--- a/src/opengl/qplatformbackingstoreopenglsupport.cpp
+++ b/src/opengl/qplatformbackingstoreopenglsupport.cpp
@@ -450,17 +450,14 @@ GLuint QPlatformBackingStoreOpenGLSupport::toTexture(const QRegion &dirtyRegion,
     return textureId;
 }
 
-static QPlatformBackingStoreOpenGLSupportBase *createOpenGLSupport()
+void qt_registerDefaultPlatformBackingStoreOpenGLSupport()
 {
-    return new QPlatformBackingStoreOpenGLSupport;
-}
-
-static void setDefaultOpenGLSupportFactoryFunction()
-{
-    if (!QPlatformBackingStoreOpenGLSupportBase::factoryFunction())
-        QPlatformBackingStoreOpenGLSupportBase::setFactoryFunction(createOpenGLSupport);
+    if (!QPlatformBackingStoreOpenGLSupportBase::factoryFunction()) {
+        QPlatformBackingStoreOpenGLSupportBase::setFactoryFunction([]() -> QPlatformBackingStoreOpenGLSupportBase* {
+            return new QPlatformBackingStoreOpenGLSupport;
+        });
+    }
 }
-Q_CONSTRUCTOR_FUNCTION(setDefaultOpenGLSupportFactoryFunction);
 
 #endif // QT_NO_OPENGL
 
diff --git a/src/opengl/qplatformbackingstoreopenglsupport.h b/src/opengl/qplatformbackingstoreopenglsupport.h
index 4821f7300f..ae9d972c6a 100644
--- a/src/opengl/qplatformbackingstoreopenglsupport.h
+++ b/src/opengl/qplatformbackingstoreopenglsupport.h
@@ -78,6 +78,8 @@ private:
     QOpenGLTextureBlitter *blitter = nullptr;
 };
 
+Q_OPENGL_EXPORT void qt_registerDefaultPlatformBackingStoreOpenGLSupport();
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_OPENGL