Expose the list of preferred instance extensions to rendercontrol users

As all QRhi stuff is private, it needs to have a public counterpart in
Qt Quick in order to fully support the case of Vulkan-based
QQuickRenderControl usage.

Change-Id: Iaf9a7aa56022acd31af6ebf16de6b83a04966ff4
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

3 files changed, 38 insertions, 5 deletions

diff --git a/src/quick/items/qquickgraphicsconfiguration.cpp b/src/quick/items/qquickgraphicsconfiguration.cpp
index dcdd069d03..4d64cf0827 100644
--- a/src/quick/items/qquickgraphicsconfiguration.cpp
+++ b/src/quick/items/qquickgraphicsconfiguration.cpp
@@ -39,6 +39,10 @@
 
 #include "qquickgraphicsconfiguration_p.h"
 
+#if QT_CONFIG(vulkan)
+#include <QtGui/private/qrhivulkan_p.h>
+#endif
+
 QT_BEGIN_NAMESPACE
 
 /*!
@@ -139,6 +143,30 @@ QQuickGraphicsConfiguration::~QQuickGraphicsConfiguration()
 }
 
 /*!
+    \return the list of Vulkan instance extensions Qt Quick prefers to
+    have enabled on the VkInstance.
+
+    In most cases Qt Quick is responsible for creating a QVulkanInstance. This
+    function is not relevant then. On the other hand, when using
+    QQuickRenderControl in combination with Vulkan-based rendering, it is the
+    application's responsibility to create a QVulkanInstance and associate it
+    with the (offscreen) QQuickWindow. In this case, it is expected that the
+    application queries the list of instance extensions to enable, and passes
+    them to QVulkanInstance::setExtensions() before calling
+    QVulkanInstance::create().
+
+    \since 6.1
+ */
+QByteArrayList QQuickGraphicsConfiguration::preferredInstanceExtensions()
+{
+#if QT_CONFIG(vulkan)
+    return QRhiVulkanInitParams::preferredInstanceExtensions();
+#else
+    return {};
+#endif
+}
+
+/*!
     Sets the list of additional \a extensions to enable on the graphics device
     (such as, the \c VkDevice).
 
diff --git a/src/quick/items/qquickgraphicsconfiguration.h b/src/quick/items/qquickgraphicsconfiguration.h
index 1c65d27502..36a14257ce 100644
--- a/src/quick/items/qquickgraphicsconfiguration.h
+++ b/src/quick/items/qquickgraphicsconfiguration.h
@@ -55,6 +55,8 @@ public:
     QQuickGraphicsConfiguration(const QQuickGraphicsConfiguration &other);
     QQuickGraphicsConfiguration &operator=(const QQuickGraphicsConfiguration &other);
 
+    static QByteArrayList preferredInstanceExtensions();
+
     void setDeviceExtensions(const QByteArrayList &extensions);
     QByteArrayList deviceExtensions() const;
 
diff --git a/src/quick/items/qquickrendercontrol.cpp b/src/quick/items/qquickrendercontrol.cpp
index c7a1ad973d..d71af669f0 100644
--- a/src/quick/items/qquickrendercontrol.cpp
+++ b/src/quick/items/qquickrendercontrol.cpp
@@ -273,10 +273,13 @@ int QQuickRenderControl::samples() const
     To configure which device extensions to enable (for example, for Vulkan),
     call QQuickWindow::setGraphicsConfiguration() before this function.
 
-    \note When using Vulkan, QQuickRenderControl does not create a
-    QVulkanInstance automatically. Rather, it is the application's
-    responsibility to create a suitable QVulkanInstance and
-    \l{QWindow::setVulkanInstance()}{associate it} with the QQuickWindow.
+    \note When using Vulkan, QQuickRenderControl does not create a QVulkanInstance
+    automatically. Rather, it is the application's responsibility to create a
+    suitable QVulkanInstance and \l{QWindow::setVulkanInstance()}{associate it} with
+    the QQuickWindow. Before initializing the QVulkanInstance, it is strongly
+    encouraged to query the list of Qt Quick's desired instance extensions by calling
+    the static function QQuickGraphicsConfiguration::preferredInstanceExtensions()
+    and to pass the returned list to QVulkanInstance::setExtensions().
 
     Returns \c true on success, \c false otherwise.
 
@@ -285,7 +288,7 @@ int QQuickRenderControl::samples() const
 
     \since 6.0
 
-    \sa QQuickRenderTarget, QQuickGraphicsDevice
+    \sa QQuickRenderTarget, QQuickGraphicsDevice, QQuickGraphicsConfiguration::preferredInstanceExtensions()
  */
 bool QQuickRenderControl::initialize()
 {