c++ - Qt3D:如何使用Qt C++在线框模式下渲染网格？

Question

Qt3D文档在增加，但是仍然缺少一些信息，尤其是没有Qml/QtQuick的情况下如何做事情。在网上搜索了大量有关以线框模式渲染网格的信息之后，我发现了许多有用的提示和示例，这些提示和示例共同产生了一个示例查看器，我想在此展示该示例查看器，以帮助所有撰写本文的人以及其他可能已经搜索了类似的示例。
最有用的链接是:
Qt basic shapes example
Qt wireframe example
Qt material documentation
Qt MyCylinder example
关于在Qt3DWindow中使用事件过滤器的Stackoverflow问答:Mouse controls over Qt 3D Window
可以使用鼠标旋转和缩放网格。
查看器的屏幕截图

欢迎对如何改善此问题发表任何评论。特别是，我对如何编写可以以不同颜色渲染正面和背面或每个顶点渲染颜色的着色器程序感兴趣。
这是代码:

// ######### Opening the viewer #########
void MainWindow::import3dMeshInMeshViewer(QString name) 
{
    if (!m_viewer3D)
    {
        m_viewer3D = new Viewer3D(this);
    }
    m_viewer3D->sceneModifier()->addTriangleMeshCustomMaterial(name, m_meshVector);
    m_viewer3D->show();
}

// #########  Viewer class h  #########
class Viewer3D : public QDialog
{
    Q_OBJECT

    public:
        Viewer3D(QWidget *parent = 0);
        SceneModifier* sceneModifier() {return m_sceneModifier;}

    protected:
        bool eventFilter(QObject *obj, QEvent *ev);
        void mouseMoveEvent(QMouseEvent *ev);
        void mousePressEvent(QMouseEvent *ev);
        void mouseReleaseEvent(QMouseEvent *ev);
        void wheelEvent(QWheelEvent *we);
    private:

        QPointer<Qt3DCore::QEntity> m_rootEntity;
        QPointer<SceneModifier> m_sceneModifier;
        Qt3DExtras::Qt3DWindow *m_view;
        QPoint m_moveStartPoint;
        QMatrix4x4 m_cameraMatrix;
};


// ######### Viewer class cpp #########
Viewer3D::Viewer3D(QWidget *parent) :
    QDialog(parent)
{
    setAttribute(Qt::WA_DeleteOnClose);
    m_moveStartPoint.setX(-1);

    m_view = new Qt3DExtras::Qt3DWindow();

    m_view->installEventFilter(this);

    m_view->defaultFrameGraph()->setClearColor(QColor(QRgb(0x4d4d4f)));

    QWidget *container = QWidget::createWindowContainer(m_view);
    QSize screenSize = m_view->screen()->size();
    container->setMinimumSize(QSize(200, 100));
    container->setMaximumSize(screenSize);

    QHBoxLayout *hLayout = new QHBoxLayout(this);
    QVBoxLayout *vLayout = new QVBoxLayout();
    hLayout->addWidget(container, 1);

    setWindowTitle(QStringLiteral("Mesh Viewer"));

    // Root entity
    m_rootEntity = new Qt3DCore::QEntity();

    // Scene modifier
    m_sceneModifier = new SceneModifier(m_rootEntity);

    // Window geometry
    resize(parent->geometry().width() * 0.8, parent->geometry().height() * 0.8);
    move(parent->geometry().center() - QPoint(width() / 2, height() / 2));

    // Camera
    Qt3DRender::QCamera *cameraEntity = m_view->camera();

    //cameraEntity->lens()->setPerspectiveProjection(22.5f, m_view->width()/m_view->height(), 0.01f, 1000.0f);
    cameraEntity->setPosition(QVector3D(0, 0, 500.0f));
    cameraEntity->setUpVector(QVector3D(0, 1, 0));
    cameraEntity->setViewCenter(QVector3D(0, 0, 0));
    cameraEntity->transform()->setScale(1.f);

    // Set root object of the scene
    m_view->setRootEntity(m_rootEntity);
}

bool Viewer3D::eventFilter(QObject *obj, QEvent *ev)
{
    if (ev->type() == QEvent::Wheel)
    {
        wheelEvent(dynamic_cast<QWheelEvent*>(ev));
        return true;
    }
    else if (ev->type() == QEvent::MouseButtonPress)
    {
        mousePressEvent(dynamic_cast<QMouseEvent*>(ev));
        return true;
    }
    else if (ev->type() == QEvent::MouseMove)
    {
        mouseMoveEvent(dynamic_cast<QMouseEvent*>(ev));
        return true;
    }
    else if (ev->type() == QEvent::MouseButtonRelease)
    {
        mouseReleaseEvent(dynamic_cast<QMouseEvent*>(ev));
        return true;
    }

    return QObject::eventFilter(obj, ev);
}

void Viewer3D::wheelEvent(QWheelEvent *we)
{
    Qt3DCore::QTransform* transform = m_view->camera()->transform();

    float scale = transform->scale();
    QPoint delta = we->angleDelta();
    float zoom_distance = scale * static_cast<float>(delta.y()) / 500.f;
    scale -= zoom_distance;
    scale = std::min(10.0000f, scale);
    scale = std::max(0.001f, scale);
    transform->setScale(scale);
}

void Viewer3D::mousePressEvent(QMouseEvent *ev)
{
    if (ev->button() == Qt::LeftButton)
    {
        m_moveStartPoint = ev->pos();
        m_cameraMatrix = m_view->camera()->transform()->matrix();
    }
}

void Viewer3D::mouseMoveEvent(QMouseEvent *ev)
{
    if (m_moveStartPoint.x() > -1)
    {
        QPoint delta = ev->pos() - m_moveStartPoint;
        float angle = static_cast<float>(QPoint::dotProduct(delta, delta)) / 100.f;
        QVector3D axis = QVector3D(delta.y(), delta.x(), 0);

        QMatrix4x4 rotationMatrix = Qt3DCore::QTransform::rotateAround(-m_view->camera()->position(), angle, axis);

        QMatrix4x4 matrix = rotationMatrix * m_cameraMatrix;
        m_view->camera()->transform()->setMatrix(matrix);
    }
}

void Viewer3D::mouseReleaseEvent(QMouseEvent *ev)
{
    if (m_moveStartPoint.x() > -1)
    {
        m_moveStartPoint.setX(-1);
        m_cameraMatrix = m_view->camera()->transform()->matrix();
    }
}


// #########  Scene modifier class h #########
class SceneModifier : public QObject
{
    Q_OBJECT

    public:
        SceneModifier(Qt3DCore::QEntity* rootEntity);
        void addTriangleMeshCustomMaterial(QString name, const std::vector<Import3d::Triangle>& meshVector);

    private:
        Qt3DCore::QEntity* m_rootEntity;
};

// #########  Scene modifier class cpp #########
#include "SceneModifier.h"
#include "TriangleMeshRenderer.h"
#include "MaterialWireFrame.h"

SceneModifier::SceneModifier(Qt3DCore::QEntity* rootEntity) :
    m_rootEntity(rootEntity),
    QObject(rootEntity)
{
}

void SceneModifier::addTriangleMeshCustomMaterial(QString name, const std::vector<Import3d::Triangle>& meshVector)
{
    if (!m_rootEntity)
    {
        return;
    }

    // Mesh entity
    Qt3DCore::QEntity *triangleMeshEntity = new Qt3DCore::QEntity(m_rootEntity);
    triangleMeshEntity->setObjectName(QStringLiteral("customMeshEntity"));

    TriangleMeshRenderer *triangleMeshRenderer = new TriangleMeshRenderer(meshVector);
    MaterialWireFrame* materialWireFrame = new MaterialWireFrame();
    Qt3DCore::QTransform *transform = new Qt3DCore::QTransform;
    transform->setScale(1.f);

    triangleMeshEntity->addComponent(triangleMeshRenderer);
    triangleMeshEntity->addComponent(transform);
    triangleMeshEntity->addComponent(materialWireFrame);

    //emit meshAdded(name, triangleMeshEntity);
}

// ######### Point and Triangle structs #########
struct Point
{
    QVector3D p; //point x, y, z
    QVector3D c; //color red, green, blue

    Point() {}

    Point(float xp, float yp, float zp)
    {
        p = QVector3D(xp, yp, zp);
        c = QVector3D(0, 0, 0);
    }
    Point(QVector3D pos, unsigned char r, unsigned char g, unsigned char b)
    {
        p = pos;
        c = QVector3D(static_cast<float>(r) / 255.f,
                      static_cast<float>(g) / 255.f,
                      static_cast<float>(b) / 255.f);
    }
};

struct Triangle 
{
    Point vertices[3];

    Triangle()
    {
    }

    Triangle(Point p1, Point p2, Point p3)
    {
        vertices[0] = p1;
        vertices[1] = p2;
        vertices[2] = p3;
    }

};


// ######### TriangleMeshRenderer class h #########
class TriangleMeshRenderer : public Qt3DRender::QGeometryRenderer
{
    Q_OBJECT
public:
    explicit TriangleMeshRenderer(const std::vector<Import3d::Triangle>& meshVector, Qt3DCore::QNode *parent = 0);
    ~TriangleMeshRenderer();
};


class TriangleMeshGeometry : public Qt3DRender::QGeometry
{
    Q_OBJECT
public:
    TriangleMeshGeometry(const std::vector<Import3d::Triangle>& meshVector, TriangleMeshRenderer *parent);
};


// ######### TriangleMeshRenderer class cpp #########
TriangleMeshRenderer::TriangleMeshRenderer(const std::vector<Import3d::Triangle>& meshVector, QNode *parent)
    : Qt3DRender::QGeometryRenderer(parent)
{
    setPrimitiveType(Qt3DRender::QGeometryRenderer::Triangles);
    setGeometry(new TriangleMeshGeometry(meshVector, this));
}

TriangleMeshRenderer::~TriangleMeshRenderer()
{
}

TriangleMeshGeometry::TriangleMeshGeometry(const std::vector<Import3d::Triangle>& meshVector, TriangleMeshRenderer *parent)
    : Qt3DRender::QGeometry(parent)
{
    Qt3DRender::QBuffer *vertexDataBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, this);
    Qt3DRender::QBuffer *indexDataBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::IndexBuffer, this);

    // Vertexbuffer
    QByteArray vertexBufferData;
    // Buffer size = triangle count * 3 * (3 + 3 + 3), 3 vertices per trinalge, each 3 floats for vertex position x,y,z, 3 floats normal and 3 floats color
    int bytesPerVertex = 9 * sizeof(float);
    int bytesPerTriangle = 3 * bytesPerVertex;
    vertexBufferData.resize(static_cast<int>(meshVector.size()) * bytesPerTriangle);
    char* pByte = vertexBufferData.data();
    int i = 0;
    // Indexbuffer
    QByteArray indexBufferData;
    indexBufferData.resize(static_cast<int>(meshVector.size()) * 3 * sizeof(uint));
    uint* rawIndexArray = reinterpret_cast<uint*>(indexBufferData.data());
    int idx = 0;

    for (int n = 0; n < meshVector.size(); ++n)
    {
        QVector3D nt = QVector3D::normal(meshVector[n].vertices[0].p, meshVector[n].vertices[1].p, meshVector[n].vertices[2].p); 

        for (int v = 0; v < 3; ++v)
        {
            // Vertex
            *reinterpret_cast<float*>(pByte) = meshVector[n].vertices[v].p.x(); pByte += 4;
            *reinterpret_cast<float*>(pByte) = meshVector[n].vertices[v].p.y(); pByte += 4;
            *reinterpret_cast<float*>(pByte) = meshVector[n].vertices[v].p.z(); pByte += 4;
            // Normal
            *reinterpret_cast<float*>(pByte) = nt.x(); pByte += 4;
            *reinterpret_cast<float*>(pByte) = nt.y(); pByte += 4;
            *reinterpret_cast<float*>(pByte) = nt.z(); pByte += 4;
            // Color
            *reinterpret_cast<float*>(pByte) = meshVector[n].vertices[v].c.x(); pByte += 4;
            *reinterpret_cast<float*>(pByte) = meshVector[n].vertices[v].c.y(); pByte += 4;
            *reinterpret_cast<float*>(pByte) = meshVector[n].vertices[v].c.z(); pByte += 4;

            // Index
            rawIndexArray[idx] = static_cast<uint>(idx++);
        }
    }

    vertexDataBuffer->setData(vertexBufferData);
    indexDataBuffer->setData(indexBufferData);

    // Attributes
    Qt3DRender::QAttribute *positionAttribute = new Qt3DRender::QAttribute();
    positionAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
    positionAttribute->setBuffer(vertexDataBuffer);
    positionAttribute->setDataType(Qt3DRender::QAttribute::Float);
    positionAttribute->setDataSize(3);
    positionAttribute->setByteOffset(0);
    positionAttribute->setByteStride(bytesPerVertex);
    positionAttribute->setCount(3 * static_cast<int>(meshVector.size()));
    positionAttribute->setName(Qt3DRender::QAttribute::defaultPositionAttributeName());

    Qt3DRender::QAttribute *normalAttribute = new Qt3DRender::QAttribute();
    normalAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
    normalAttribute->setBuffer(vertexDataBuffer);
    normalAttribute->setDataType(Qt3DRender::QAttribute::Float);
    normalAttribute->setDataSize(3);
    normalAttribute->setByteOffset(3 * sizeof(float));
    normalAttribute->setByteStride(bytesPerVertex);
    normalAttribute->setCount(3 * static_cast<int>(meshVector.size()));
    normalAttribute->setName(Qt3DRender::QAttribute::defaultNormalAttributeName());

    Qt3DRender::QAttribute *colorAttribute = new Qt3DRender::QAttribute();
    colorAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
    colorAttribute->setBuffer(vertexDataBuffer);
    colorAttribute->setDataType(Qt3DRender::QAttribute::Float);
    colorAttribute->setDataSize(3);
    colorAttribute->setByteOffset(6 * sizeof(float));
    colorAttribute->setByteStride(bytesPerVertex);
    colorAttribute->setCount(3 * static_cast<int>(meshVector.size()));
    colorAttribute->setName(Qt3DRender::QAttribute::defaultColorAttributeName());

    Qt3DRender::QAttribute *indexAttribute = new Qt3DRender::QAttribute();
    indexAttribute->setAttributeType(Qt3DRender::QAttribute::IndexAttribute);
    indexAttribute->setBuffer(indexDataBuffer);
    indexAttribute->setDataType(Qt3DRender::QAttribute::UnsignedInt);
    indexAttribute->setDataSize(1);
    indexAttribute->setByteOffset(0);
    indexAttribute->setByteStride(0);
    indexAttribute->setCount(3 * static_cast<int>(meshVector.size()));

    addAttribute(positionAttribute);
    addAttribute(normalAttribute);
    addAttribute(colorAttribute);
    addAttribute(indexAttribute);

    parent->setGeometry(this);
}

Answer 1

OP对编写着色器程序感兴趣，因此有必要在Qt中编写OpenGL，对吗？就像https://doc.qt.io/qt-5/qtgui-openglwindow-example.html和https://doc.qt.io/qt-5/qtopengl-hellogl2-example.htm一样。
https://doc.qt.io/qt-5/qopenglshaderprogram.html上有一个简单的着色器示例

program.addShaderFromSourceCode(QOpenGLShader::Vertex,
    "attribute highp vec4 vertex;\n"
    "uniform highp mat4 matrix;\n"
    "void main(void)\n"
    "{\n"
    "   gl_Position = matrix * vertex;\n"
    "}");
program.addShaderFromSourceCode(QOpenGLShader::Fragment,
    "uniform mediump vec4 color;\n"
    "void main(void)\n"
    "{\n"
    "   gl_FragColor = color;\n"
    "}");

从https://learnopengl.com/Getting-started/Hello-Triangle

To draw your triangles in wireframe mode, you can configure how OpenGL draws its primitives via glPolygonMode(GL_FRONT_AND_BACK, GL_LINE). The first argument says we want to apply it to the front and back of all triangles and the second line tells us to draw them as lines. Any subsequent drawing calls will render the triangles in wireframe mode until we set it back to its default using glPolygonMode(GL_FRONT_AND_BACK, GL_FILL).

从https://learnopengl.com/Advanced-OpenGL/Advanced-GLSL

The gl_FrontFacing variable tells us if the current fragment is part of a front-facing or a back-facing face. We could, for example, decide to output different colors for all back faces.