rhi: vulkan: expose the instance in the nativeHandles query

Mainly for completeness, but it has practical uses: someone retrieving
a QRhi instance from somewhere should be able to tell the
QVulkanInstance, and so the VkInstance, used by that QRhi without
resorting to investigating other objects (e.g. retrieving the instance
from the QWindow). This provides symmetry to other 3D APIs and QRhi
backends where just a single QRhi instance is sufficient to get the
MTLDevice, ID3D11Device/Context, etc. i.e. all that is needed to
work with the 3D API directly.

Change-Id: I5a8b9871a543ea648c76b868bf6ff7be5f2098f2
Reviewed-by: Jonas Karlsson <jonas.karlsson@qt.io>
Reviewed-by: Hatem ElKharashy <hatem.elkharashy@qt.io>

src/gui/rhi/qrhi_platform.h

@@ -86,9 +86,12 @@ struct Q_GUI_EXPORT QRhiVulkanNativeHandles : public QRhiNativeHandles
     VkDevice dev = VK_NULL_HANDLE;
     quint32 gfxQueueFamilyIdx = 0;
     quint32 gfxQueueIdx = 0;
-    VkQueue gfxQueue = VK_NULL_HANDLE;
     // and optionally, the mem allocator
     void *vmemAllocator = nullptr;
+
+    // only for querying (rhi->nativeHandles())
+    VkQueue gfxQueue = VK_NULL_HANDLE;
+    QVulkanInstance *inst = nullptr;
 };
 
 struct Q_GUI_EXPORT QRhiVulkanCommandBufferNativeHandles : public QRhiNativeHandles

src/gui/rhi/qrhivulkan.cpp

@@ -225,6 +225,13 @@ QT_BEGIN_NAMESPACE
     Graphics queue index.
 */
 
+/*!
+    \variable QRhiVulkanNativeHandles::vmemAllocator
+
+    Relevant only when importing an existing memory allocator object,
+    leave it set to \nullptr otherwise.
+*/
+
 /*!
     \variable QRhiVulkanNativeHandles::gfxQueue
 
@@ -233,10 +240,10 @@ QT_BEGIN_NAMESPACE
 */
 
 /*!
-    \variable QRhiVulkanNativeHandles::vmemAllocator
+    \variable QRhiVulkanNativeHandles::inst
 
-    Relevant only when importing an existing memory allocator object,
-    leave it set to \nullptr otherwise.
+    Output only, not used by QRhi::create(), only set by the
+    QRhi::nativeHandles() accessor. The QVulkanInstance used by the QRhi.
 */
 
 /*!
@@ -819,6 +826,7 @@ bool QRhiVulkan::create(QRhi::Flags flags)
     nativeHandlesStruct.gfxQueueIdx = gfxQueueIdx;
     nativeHandlesStruct.gfxQueue = gfxQueue;
     nativeHandlesStruct.vmemAllocator = allocator;
+    nativeHandlesStruct.inst = inst;
 
     return true;
 }

tests/auto/gui/rhi/qrhi/tst_qrhi.cpp

@@ -487,6 +487,8 @@ void tst_QRhi::nativeHandles()
         case QRhi::Vulkan:
         {
             const QRhiVulkanNativeHandles *vkHandles = static_cast<const QRhiVulkanNativeHandles *>(rhiHandles);
+            QVERIFY(vkHandles->inst);
+            QCOMPARE(vkHandles->inst, &vulkanInstance);
             QVERIFY(vkHandles->physDev);
             QVERIFY(vkHandles->dev);
             QVERIFY(vkHandles->gfxQueue);