Qt Quick 3D - Stencil Outline Extension Example

 // Copyright (C) 2023 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

 #ifndef OUTLINERENDEREXTENSION_H
 #define OUTLINERENDEREXTENSION_H

 #include <QtQuick3D/qquick3drenderextensions.h>
 #include <QtQmlIntegration>

 class OutlineRenderExtension : public QQuick3DRenderExtension
 {
     Q_OBJECT
     Q_PROPERTY(QQuick3DObject * target READ target WRITE setTarget NOTIFY targetChanged)
     Q_PROPERTY(QQuick3DObject * outlineMaterial READ outlineMaterial WRITE setOutlineMaterial NOTIFY outlineMaterialChanged)
     Q_PROPERTY(float outlineScale READ outlineScale WRITE setOutlineScale NOTIFY outlineScaleChanged)
     QML_ELEMENT

 public:
     OutlineRenderExtension() = default;
     ~OutlineRenderExtension() override;

     float outlineScale() const;
     void setOutlineScale(float newOutlineScale);

     QQuick3DObject *target() const;
     void setTarget(QQuick3DObject *newTarget);

     QQuick3DObject *outlineMaterial() const;
     void setOutlineMaterial(QQuick3DObject *newOutlineMaterial);

 signals:
     void outlineColorChanged();
     void outlineScaleChanged();
     void targetChanged();
     void outlineMaterialChanged();

 protected:
     QSSGRenderGraphObject *updateSpatialNode(QSSGRenderGraphObject *node) override;

 private:
     enum Dirty : quint8
     {
         Target = 1 << 0,
         OutlineMaterial = 1 << 1,
         OutlineScale = 1 << 2
     };

     using DirtyT = std::underlying_type_t<Dirty>;

     void markDirty(Dirty v);

     QPointer<QQuick3DObject> m_target;
     QPointer<QQuick3DObject> m_outlineMaterial;
     float m_outlineScale = 1.05f;
     DirtyT m_dirtyFlag {};
 };

 #endif // OUTLINERENDEREXTENSION_H