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.

Pick-to: 6.1
Fixes: QTBUG-90665
Change-Id: I53081bac382ab89573359886e4f5c4b41be8e86d
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>

4 files changed, 7 insertions, 4 deletions

diff --git a/tests/manual/qmldynamicdata/qml/qmldynamicdata/main.qml b/tests/manual/qmldynamicdata/qml/qmldynamicdata/main.qml
index 25bf3486..74ec5cb9 100644
--- a/tests/manual/qmldynamicdata/qml/qmldynamicdata/main.qml
+++ b/tests/manual/qmldynamicdata/qml/qmldynamicdata/main.qml
@@ -32,7 +32,7 @@ import QtDataVisualization 1.2
 import QtQuick.Controls
 import "."
 
-Rectangle {
+Item {
     id: mainView
     width: 1280
     height: 720
diff --git a/tests/manual/qmlgradient/qml/qmlgradient/main.qml b/tests/manual/qmlgradient/qml/qmlgradient/main.qml
index 7df90def..c692a72a 100644
--- a/tests/manual/qmlgradient/qml/qmlgradient/main.qml
+++ b/tests/manual/qmlgradient/qml/qmlgradient/main.qml
@@ -34,7 +34,7 @@ import QtQuick.Controls
 import QtDataVisualization 1.2
 import "."
 
-Rectangle {
+Item {
     id: mainwindow
 
     function updateinfoLabels()
diff --git a/tests/manual/qmlmultitest/qml/qmlmultitest/main.qml b/tests/manual/qmlmultitest/qml/qmlmultitest/main.qml
index 890f9479..54c85e95 100644
--- a/tests/manual/qmlmultitest/qml/qmlmultitest/main.qml
+++ b/tests/manual/qmlmultitest/qml/qmlmultitest/main.qml
@@ -33,7 +33,7 @@ import QtQuick.Controls
 import QtDataVisualization 1.2
 import "."
 
-Rectangle {
+Item {
     id: mainView
     width: 800
     height: 600
@@ -57,6 +57,7 @@ Rectangle {
             Layout.fillWidth: true
             border.color: surfaceGraph.theme.gridLineColor
             border.width: 2
+            color: "#00000000"
 
             Surface3D {
                 id: surfaceGraph
@@ -145,6 +146,7 @@ Rectangle {
             Layout.fillWidth: true
             border.color: scatterGraph.theme.gridLineColor
             border.width: 2
+            color: "#00000000"
 
             Scatter3D {
                 id: scatterGraph
@@ -185,6 +187,7 @@ Rectangle {
             Layout.fillWidth: true
             border.color: barGraph.theme.gridLineColor
             border.width: 2
+            color: "#00000000"
 
             Bars3D {
                 id: barGraph
diff --git a/tests/manual/qmlperf/qml/qmlperf/main.qml b/tests/manual/qmlperf/qml/qmlperf/main.qml
index 1ff64ad5..60930606 100644
--- a/tests/manual/qmlperf/qml/qmlperf/main.qml
+++ b/tests/manual/qmlperf/qml/qmlperf/main.qml
@@ -33,7 +33,7 @@ import QtQuick.Controls
 import QtDataVisualization 1.2
 import "."
 
-Rectangle {
+Item {
     id: mainview
     width: 1280
     height: 1024