Qt Quick 3D - Custom Geometry Example

 // Copyright (C) 2020 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

 #include "examplegeometry.h"
 #include <QRandomGenerator>
 #include <QVector3D>

 ExampleTriangleGeometry::ExampleTriangleGeometry()
 {
     updateData();
 }

 void ExampleTriangleGeometry::setNormals(bool enable)
 {
     if (m_hasNormals == enable)
         return;

     m_hasNormals = enable;
     emit normalsChanged();
     updateData();
     update();
 }

 void ExampleTriangleGeometry::setNormalXY(float xy)
 {
     if (m_normalXY == xy)
         return;

     m_normalXY = xy;
     emit normalXYChanged();
     updateData();
     update();
 }

 void ExampleTriangleGeometry::setUV(bool enable)
 {
     if (m_hasUV == enable)
         return;

     m_hasUV = enable;
     emit uvChanged();
     updateData();
     update();
 }

 void ExampleTriangleGeometry::setUVAdjust(float f)
 {
     if (m_uvAdjust == f)
         return;

     m_uvAdjust = f;
     emit uvAdjustChanged();
     updateData();
     update();
 }

 void ExampleTriangleGeometry::updateData()
 {
     clear();

     int stride = 3 * sizeof(float);
     if (m_hasNormals)
         stride += 3 * sizeof(float);
     if (m_hasUV)
         stride += 2 * sizeof(float);

     QByteArray vertexData(3 * stride, Qt::Initialization::Uninitialized);
     float *p = reinterpret_cast<float *>(vertexData.data());

     // a triangle, front face = counter-clockwise
     *p++ = -1.0f; *p++ = -1.0f; *p++ = 0.0f;
     if (m_hasNormals) {
         *p++ = m_normalXY; *p++ = m_normalXY; *p++ = 1.0f;
     }
     if (m_hasUV) {
         *p++ = 0.0f + m_uvAdjust; *p++ = 0.0f + m_uvAdjust;
     }
     *p++ = 1.0f; *p++ = -1.0f; *p++ = 0.0f;
     if (m_hasNormals) {
         *p++ = m_normalXY; *p++ = m_normalXY; *p++ = 1.0f;
     }
     if (m_hasUV) {
         *p++ = 1.0f - m_uvAdjust; *p++ = 0.0f + m_uvAdjust;
     }
     *p++ = 0.0f; *p++ = 1.0f; *p++ = 0.0f;
     if (m_hasNormals) {
         *p++ = m_normalXY; *p++ = m_normalXY; *p++ = 1.0f;
     }
     if (m_hasUV) {
         *p++ = 1.0f - m_uvAdjust; *p++ = 1.0f - m_uvAdjust;
     }

     setVertexData(vertexData);
     setStride(stride);
     setBounds(QVector3D(-1.0f, -1.0f, 0.0f), QVector3D(+1.0f, +1.0f, 0.0f));

     setPrimitiveType(QQuick3DGeometry::PrimitiveType::Triangles);

     addAttribute(QQuick3DGeometry::Attribute::PositionSemantic,
                  0,
                  QQuick3DGeometry::Attribute::F32Type);

     if (m_hasNormals) {
         addAttribute(QQuick3DGeometry::Attribute::NormalSemantic,
                      3 * sizeof(float),
                      QQuick3DGeometry::Attribute::F32Type);
     }

     if (m_hasUV) {
         addAttribute(QQuick3DGeometry::Attribute::TexCoordSemantic,
                      m_hasNormals ? 6 * sizeof(float) : 3 * sizeof(float),
                      QQuick3DGeometry::Attribute::F32Type);
     }
 }

 ExamplePointGeometry::ExamplePointGeometry()
 {
     updateData();
 }

 void ExamplePointGeometry::updateData()
 {
     clear();

     constexpr auto randomFloat = [](const float lowest, const float highest) -> float {
         return lowest + QRandomGenerator::global()->generateDouble() * (highest - lowest);
     };
     constexpr int NUM_POINTS = 2000;
     constexpr int stride = 3 * sizeof(float);

     QByteArray vertexData;
     vertexData.resize(NUM_POINTS * stride);
     float *p = reinterpret_cast<float *>(vertexData.data());

     for (int i = 0; i < NUM_POINTS; ++i) {
         *p++ = randomFloat(-5.0f, +5.0f);
         *p++ = randomFloat(-5.0f, +5.0f);
         *p++ = 0.0f;
     }

     setVertexData(vertexData);
     setStride(stride);
     setBounds(QVector3D(-5.0f, -5.0f, 0.0f), QVector3D(+5.0f, +5.0f, 0.0f));

     setPrimitiveType(QQuick3DGeometry::PrimitiveType::Points);

     addAttribute(QQuick3DGeometry::Attribute::PositionSemantic,
                  0,
                  QQuick3DGeometry::Attribute::F32Type);
 }