Fix direct rendering doesn't show anything

Rendering a graph directly to background didn't
work in Qt 6 since it uses RHI and there is
no way to not clear the color buffer
before rendering. The graph uses direct OpenGL
calls to render directly to background. Enabled
direct rendering to qml3doscilloscope example.
In addition, RenderDirectToBackground_NoClear got
deprecated.

When rendering directly to background,
using non-transparent qml item as a background
will hide the graph. This was already mentioned
in the documentation but not clearly enough.
Updated documentation for AbstractGraph3D.

Fixes: QTBUG-90665
Change-Id: I53081bac382ab89573359886e4f5c4b41be8e86d
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>
(cherry picked from commit ad85513d4b38bdedac27a095bd3a988f1eda23a2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

9 files changed, 12 insertions, 10 deletions

diff --git a/examples/datavisualization/qml3doscilloscope/doc/src/qml3doscilloscope.qdoc b/examples/datavisualization/qml3doscilloscope/doc/src/qml3doscilloscope.qdoc
index 3772df32..a3b2f3f3 100644
--- a/examples/datavisualization/qml3doscilloscope/doc/src/qml3doscilloscope.qdoc
+++ b/examples/datavisualization/qml3doscilloscope/doc/src/qml3doscilloscope.qdoc
@@ -110,7 +110,6 @@
 
     \snippet qml3doscilloscope/qml/qml3doscilloscope/main.qml 3
 
-    \omit
     \section1 Enabling Direct Rendering
 
     Since this application potentially deals with a lot of rapidly changing data, we use direct
@@ -122,6 +121,5 @@
     \snippet qml3doscilloscope/main.cpp 1
     \dots 0
     \snippet qml3doscilloscope/main.cpp 2
-    \endomit
 
 */
diff --git a/examples/datavisualization/qml3doscilloscope/qml/qml3doscilloscope/main.qml b/examples/datavisualization/qml3doscilloscope/qml/qml3doscilloscope/main.qml
index ba733c21..51eba416 100644
--- a/examples/datavisualization/qml3doscilloscope/qml/qml3doscilloscope/main.qml
+++ b/examples/datavisualization/qml3doscilloscope/qml/qml3doscilloscope/main.qml
@@ -74,6 +74,7 @@ Item {
             axisY.segmentCount: 4
             axisZ.segmentCount: 4
             measureFps: true
+            renderingMode: AbstractGraph3D.RenderDirectToBackground
 
             onCurrentFpsChanged: (fps)=> {
                 if (fps > 10)
diff --git a/examples/datavisualization/qmlaxisformatter/qml/qmlaxisformatter/main.qml b/examples/datavisualization/qmlaxisformatter/qml/qmlaxisformatter/main.qml
index 7be207af..d7042535 100644
--- a/examples/datavisualization/qmlaxisformatter/qml/qmlaxisformatter/main.qml
+++ b/examples/datavisualization/qmlaxisformatter/qml/qmlaxisformatter/main.qml
@@ -34,7 +34,7 @@ import QtDataVisualization 1.2
 import CustomFormatter
 import "."
 
-Rectangle {
+Item {
     id: mainView
     width: 1280
     height: 1024
diff --git a/examples/datavisualization/qmlbars/qml/qmlbars/main.qml b/examples/datavisualization/qmlbars/qml/qmlbars/main.qml
index ab855fd9..76eff0f2 100644
--- a/examples/datavisualization/qmlbars/qml/qmlbars/main.qml
+++ b/examples/datavisualization/qmlbars/qml/qmlbars/main.qml
@@ -35,7 +35,7 @@ import QtQuick.Window
 import Qt.labs.qmlmodels
 import "."
 
-Rectangle {
+Item {
     id: mainview
     width: 1280
     height: 1024
diff --git a/examples/datavisualization/qmlcustominput/qml/qmlcustominput/main.qml b/examples/datavisualization/qmlcustominput/qml/qmlcustominput/main.qml
index 23fb13ee..77576127 100644
--- a/examples/datavisualization/qmlcustominput/qml/qmlcustominput/main.qml
+++ b/examples/datavisualization/qmlcustominput/qml/qmlcustominput/main.qml
@@ -33,7 +33,7 @@ import QtQuick.Controls
 import QtDataVisualization 1.2
 import "."
 
-Rectangle {
+Item {
     id: mainView
     width: 1280
     height: 720
diff --git a/examples/datavisualization/qmllegend/qml/qmllegend/main.qml b/examples/datavisualization/qmllegend/qml/qmllegend/main.qml
index 5100a378..5245fd67 100644
--- a/examples/datavisualization/qmllegend/qml/qmllegend/main.qml
+++ b/examples/datavisualization/qmllegend/qml/qmllegend/main.qml
@@ -33,7 +33,7 @@ import QtQuick.Layouts
 import QtDataVisualization 1.2
 import "."
 
-Rectangle {
+Item {
     id: mainView
     width: 800
     height: 600
diff --git a/examples/datavisualization/qmlmultigraph/qml/qmlmultigraph/main.qml b/examples/datavisualization/qmlmultigraph/qml/qmlmultigraph/main.qml
index cbfeb9d8..f30b1739 100644
--- a/examples/datavisualization/qmlmultigraph/qml/qmlmultigraph/main.qml
+++ b/examples/datavisualization/qmlmultigraph/qml/qmlmultigraph/main.qml
@@ -33,7 +33,7 @@ import QtQuick.Controls
 import QtDataVisualization 1.2
 import "."
 
-Rectangle {
+Item {
     id: mainView
     width: 800
     height: 600
@@ -58,6 +58,7 @@ Rectangle {
             Layout.fillWidth: true
             border.color: surfaceGraph.theme.gridLineColor
             border.width: 2
+            color: "#00000000"
 
             Surface3D {
                 id: surfaceGraph
@@ -134,6 +135,7 @@ Rectangle {
             Layout.fillWidth: true
             border.color: scatterGraph.theme.gridLineColor
             border.width: 2
+            color: "#00000000"
 
             Scatter3D {
                 id: scatterGraph
@@ -163,6 +165,7 @@ Rectangle {
             Layout.fillWidth: true
             border.color: barGraph.theme.gridLineColor
             border.width: 2
+            color: "#00000000"
 
             Bars3D {
                 id: barGraph
diff --git a/examples/datavisualization/qmlscatter/doc/src/qmlscatter.qdoc b/examples/datavisualization/qmlscatter/doc/src/qmlscatter.qdoc
index 667aea49..95d2bc66 100644
--- a/examples/datavisualization/qmlscatter/doc/src/qmlscatter.qdoc
+++ b/examples/datavisualization/qmlscatter/doc/src/qmlscatter.qdoc
@@ -80,11 +80,11 @@
     The last \c import just imports all the qml files in the same directory as our \c {main.qml},
     because that's where \c Data.qml is.
 
-    Then we create our main \c Rectangle and call it \c mainView:
+    Then we create our main \c Item and call it \c mainView:
 
     \snippet qmlscatter/qml/qmlscatter/main.qml 1
 
-    Then we'll add another \c Item inside the main \c Rectangle, and call it \c dataView.
+    Then we'll add another \c Item inside the main \c Item, and call it \c dataView.
     This will be the item to hold the Scatter3D graph. We'll anchor it to the parent bottom:
 
     \snippet qmlscatter/qml/qmlscatter/main.qml 9
diff --git a/examples/datavisualization/qmlscatter/qml/qmlscatter/main.qml b/examples/datavisualization/qmlscatter/qml/qmlscatter/main.qml
index bafbfc57..89863d84 100644
--- a/examples/datavisualization/qmlscatter/qml/qmlscatter/main.qml
+++ b/examples/datavisualization/qmlscatter/qml/qmlscatter/main.qml
@@ -36,7 +36,7 @@ import "."
 //! [0]
 
 //! [1]
-Rectangle {
+Item {
     id: mainView
     //! [1]
     width: 500