Refactor Scene3D to work with both RHI and GL Qt3D renderers

- Depending on whether we are using RHI or GL we need to either trigger
  the rendering after the beforeRendering or beforeRenderPassRecording
  have been fired

  -> beforeRendering
     The RHI command buffer is set up but nothing has been
     recorded yet. This is what we want for the RHI backend
     but we will need to make sure we don't call begin/endFrame
     nor use swap chains other than the one QtQuick is using.
     This means RenderSurfaceSelector won't be possible.

  -> beforeRenderPassRecording
     The RHI command for buffer uploads have been uploaded but the
     actual RenderPass draw calls have yet to be made. The screen
     has been cleared already, so this is the best place for the
     GL backend which expects the screen to have been cleared.

- The GL backend can use a QOpenGLFrameBufferObject but that is not
  possible with the RHI backend.
- The RHI backend uses a custom QRhiRenderTarget that takes care of
  blitting its color attachment into a QRhiTexture which is then
  bound to a QSGTexture

The overall Scene3DItem/Scene3DRender architecture remains the same:
- processChange
- Render Qt3D content into Texture
- Set texture on a custom QSGNode quad

Change-Id: Id6c317342d0a227d5295cbfefefc3ed12da160d7
Reviewed-by: Mike Krus <mike.krus@kdab.com>

4 files changed, 16 insertions, 28 deletions

diff --git a/src/render/backend/abstractrenderer_p.h b/src/render/backend/abstractrenderer_p.h
index 6f849128a..2eec1bc1b 100644
--- a/src/render/backend/abstractrenderer_p.h
+++ b/src/render/backend/abstractrenderer_p.h
@@ -69,6 +69,9 @@ class QScreen;
 class QOpenGLTexture;
 class QMouseEvent;
 class QKeyEvent;
+class QRhi;
+class QRhiRenderTarget;
+class QRhiCommandBuffer;
 
 namespace Qt3DCore {
 class QAbstractFrameAdvanceService;
@@ -118,9 +121,16 @@ public:
     };
     Q_DECLARE_FLAGS(BackendNodeDirtySet, BackendNodeDirtyFlag)
 
+    enum RenderDriver {
+        Qt3D,
+        Scene3D,
+    };
+
     virtual void dumpInfo() const = 0;
 
     virtual API api() const = 0;
+    virtual void setRenderDriver(RenderDriver driver) = 0;
+    virtual RenderDriver renderDriver() const = 0;
 
     virtual qint64 time() const = 0;
     virtual void setTime(qint64 time) = 0;
@@ -172,8 +182,11 @@ public:
 
     virtual QVariant executeCommand(const QStringList &args) = 0;
 
-    // For QtQuick rendering (Scene2D)
+    // For QtQuick rendering (Scene3D/2D)
     virtual void setOpenGLContext(QOpenGLContext *ctx) = 0;
+    virtual void setRHIContext(QRhi *ctx) = 0;
+    virtual void setDefaultRHIRenderTarget(QRhiRenderTarget *defaultTarget) = 0;
+    virtual void setRHICommandBuffer(QRhiCommandBuffer *commandBuffer) = 0;
     virtual void setScreen(QScreen *) {}
     virtual QScreen *screen() const { return nullptr; }
     virtual bool accessOpenGLTexture(Qt3DCore::QNodeId nodeId, QOpenGLTexture **texture, QMutex **lock, bool readonly) = 0;
diff --git a/src/render/frontend/qrenderapi.h b/src/render/frontend/qrenderapi.h
index fc046642a..df1a4a692 100644
--- a/src/render/frontend/qrenderapi.h
+++ b/src/render/frontend/qrenderapi.h
@@ -51,6 +51,7 @@ enum class API {
     Vulkan,
     DirectX,
     Metal,
+    RHI,
     Null
 };
 
diff --git a/src/render/frontend/qrenderaspect.cpp b/src/render/frontend/qrenderaspect.cpp
index bd6d7d831..3c5c2c053 100644
--- a/src/render/frontend/qrenderaspect.cpp
+++ b/src/render/frontend/qrenderaspect.cpp
@@ -630,29 +630,6 @@ QRenderAspect::~QRenderAspect()
 {
 }
 
-// Called by Scene3DRenderer only
-void QRenderAspectPrivate::renderInitialize(QOpenGLContext *context)
-{
-    if (m_renderer->api() == API::OpenGL)
-        m_renderer->setOpenGLContext(context);
-    m_renderer->initialize();
-}
-
-/*! \internal */
-void QRenderAspectPrivate::render(bool swapBuffers)
-{
-    m_renderer->render(swapBuffers);
-}
-
-/*
- * \internal
- * Only called when rendering with QtQuick 2 and a Scene3D item
- */
-void QRenderAspectPrivate::renderShutdown()
-{
-    m_renderer->shutdown();
-}
-
 std::vector<Qt3DCore::QAspectJobPtr> QRenderAspect::jobsToExecute(qint64 time)
 {
     using namespace Render;
diff --git a/src/render/frontend/qrenderaspect_p.h b/src/render/frontend/qrenderaspect_p.h
index 71dcf0468..b1b7bedc3 100644
--- a/src/render/frontend/qrenderaspect_p.h
+++ b/src/render/frontend/qrenderaspect_p.h
@@ -71,7 +71,7 @@ QT_BEGIN_NAMESPACE
 
 class QSurface;
 class QScreen;
-
+class QRhi;
 namespace Qt3DRender {
 
 class QSceneImporter;
@@ -113,9 +113,6 @@ public:
     void unregisterBackendTypes();
     void loadSceneParsers();
     void loadRenderPlugin(const QString &pluginName);
-    void renderInitialize(QOpenGLContext *context);
-    void render(bool swapBuffers = true);
-    void renderShutdown();
     void registerBackendType(const QMetaObject &, const Qt3DCore::QBackendNodeMapperPtr &functor);
     std::vector<Qt3DCore::QAspectJobPtr> createGeometryRendererJobs() const;
     std::vector<Qt3DCore::QAspectJobPtr> createPreRendererJobs() const;