rendernode example: Add support for Metal

Plus clarify QQuickWindow::begin/endExternalCommands() in combination
with QSGRenderNode in the docs. As the example demonstrates, calling
these functions is not necessary within render() of a render node.

Also fix an issue with resetting the scissor in the renderer after
calling render() of a QSGRenderNode.

Change-Id: If8c2dab38d62aa444266d37901f062a51e767f68
Reviewed-by: Christian Strømme <christian.stromme@qt.io>

2 files changed, 16 insertions, 3 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index 88a731b229..8b5e2a012a 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -4666,6 +4666,11 @@ const QQuickWindow::GraphicsStateInfo *QQuickWindow::graphicsStateInfo()
     beginExternalCommands() and endExternalCommands() together provide a
     replacement for resetOpenGLState().
 
+    Calling this function and endExternalCommands() is not necessary within the
+    \l{QSGRenderNode::render()}{render()} implementation of a QSGRenderNode
+    because the scene graph performs the necessary steps implicitly for render
+    nodes.
+
     \note This function has no effect when the scene graph is using OpenGL
     directly and the RHI graphics abstraction layer is not in use. Refer to
     resetOpenGLState() in that case.
@@ -4704,6 +4709,11 @@ void QQuickWindow::beginExternalCommands()
     beginExternalCommands() and endExternalCommands() together provide a
     replacement for resetOpenGLState().
 
+    Calling this function and beginExternalCommands() is not necessary within the
+    \l{QSGRenderNode::render()}{render()} implementation of a QSGRenderNode
+    because the scene graph performs the necessary steps implicitly for render
+    nodes.
+
     \note This function has no effect when the scene graph is using OpenGL
     directly and the RHI graphics abstraction layer is not in use. Refer to
     resetOpenGLState() in that case.
diff --git a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
index 293cc4cb6b..2441e14fda 100644
--- a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
+++ b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
@@ -4563,11 +4563,14 @@ void Renderer::renderRhiRenderNode(const Batch *batch) // split prepare-render (
     rd->m_matrix = nullptr;
     rd->m_clip_list = nullptr;
 
-    if (changes & QSGRenderNode::ViewportState)
+    if ((changes & QSGRenderNode::ViewportState)
+            || (changes & QSGRenderNode::ScissorState))
+    {
+        // Reset both flags if either is reported as changed, since with the rhi
+        // it could be setViewport() that will record the resetting of the scissor.
         m_pstate.viewportSet = false;
-
-    if (changes & QSGRenderNode::ScissorState)
         m_pstate.scissorSet = false;
+    }
 
     // Do not bother with RenderTargetState. Where applicable, endExternal()
     // ensures the correct target is rebound. For others (like Vulkan) it makes