訪問Qt3D中的framebuffer

Question

我的任務：計算3D網格的像素坐標（例如制作快照），從特定的攝像機角度找到該網格的2D形狀。

我目前正在使用帶有QGeometryRenderer的Qt3D將包含網格的場景渲染到QWidget，它可以正常工作。 我嘗試使用QWidget :: render（）將QWidget的內容呈現為Pixmap，如本文所建議的如何創建QWidget的屏幕截圖？ 。 將像素圖保存為.jpg會產生具有默認背景顏色的空白圖像，這是有意義的，因為QWidget本身並未保存網格對象。

以下是我在mainwindow.cpp中設置場景的方法

// sets the scene objects, camera, lights,...
void MainWindow::setScene() {
    scene = custommesh->createScene(mesh->getVertices(), 
            mesh->getVerticesNormals(), 
            mesh->getFaceNormals(), 
            mesh->getVerticesIndex(), 
            mesh->getFacesIndex());              // QEntity*                         
    custommesh->setMaterial(scene);              // CustomMeshRenderer object
    camera = custommesh->setCamera(view);
    custommesh->setLight(scene, camera);
    custommesh->setCamController(scene, camera);

    view->setRootEntity(scene);                  // Qt3DExtras::Qt3DWindow object

    // Setting up a QWiget working as a container for the view
    QWidget *container = QWidget::createWindowContainer(view);
    container->setMinimumSize(QSize(500, 500));
    QSizePolicy policy = QSizePolicy(QSizePolicy::Policy(5), QSizePolicy::Policy(5));
    policy.setHorizontalStretch(1);
    policy.setVerticalStretch(1);
    container->setSizePolicy(policy);
    container->setObjectName("meshWidget");

    this->ui->meshLayout->insertWidget(0, container);
}

至於渲染，這里是custommeshrenderer類，其中定義了QGeometryRenderer，並在初始化網格時返回QEntity *。

#include "custommeshrenderer.h"
#include <Qt3DRender/QAttribute>
#include <Qt3DExtras>
#include <Qt3DRender/QGeometryRenderer>


CustommeshRenderer::CustommeshRenderer()
{
    rootEntity = new Qt3DCore::QEntity;
    customMeshEntity = new Qt3DCore::QEntity(rootEntity);
    transform = new Qt3DCore::QTransform;

    customMeshRenderer = new Qt3DRender::QGeometryRenderer;
    customGeometry = new Qt3DRender::QGeometry(customMeshRenderer);

    m_pVertexDataBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, customGeometry);
    m_pNormalDataBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, customGeometry);
    m_pColorDataBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, customGeometry);
    m_pIndexDataBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::IndexBuffer, customGeometry);

}

/**
    Set vertices and their normals for the scene

    @param vertices List with all vertices of the mesh
    @param vertices_normals List with all vertice normals
    @param face_normals List with all face normals
    @param vertice_idx List with the indices for the vertices
    @param face_idx List with all indices for the faces
    @return Entity where some components were added
*/
Qt3DCore::QEntity *CustommeshRenderer::createScene(QList<QVector3D> vertices, QList<QVector3D> vertices_normals, QList<QVector3D> face_normals, QList<int> vertices_idx, QList<QVector3D> faces_idx) {

    // Setting scale to 8.0
    transform->setScale(8.0f);

    // Setting all the colors to (200, 0, 0)
    QList<QVector3D> color_list;
    for(int i = 0; i < vertices.length(); i++) {
        color_list.append(QVector3D(200.0f, 0.0f, 0.0f));
    }

    // Fill vertexBuffer with data which hold the vertices, normals and colors
    // Build structure: Size of Verticles List * 3 (x,y,z) * 4 (since x,y,z are floats, which needs 4 bytes each) 
    vertexBufferData.resize(vertices.length() * 3 * (int)sizeof(float));
    float *rawVertexArray = reinterpret_cast<float *>(vertexBufferData.data());

    normalBufferData.resize(vertices_normals.length() * 3 * (int)sizeof(float));
    float *rawNormalArray = reinterpret_cast<float *>(normalBufferData.data());

    colorBufferData.resize(color_list.length() * 3 * (int)sizeof(float));
    float *rawColorArray = reinterpret_cast<float *>(colorBufferData.data());


    setRawVertexArray(rawVertexArray, vertices);
    setRawNormalArray(rawNormalArray, vertices_normals);
    setRawColorArray(rawColorArray, color_list);

    //Fill indexBufferData with data which holds the triangulation information (patches/tris/lines)
    indexBufferData.resize(faces_idx.length() * 3 * (int)sizeof(uint));
    uint *rawIndexArray = reinterpret_cast<uint *>(indexBufferData.data());

    setRawIndexArray(rawIndexArray, faces_idx);

    //Set data to buffers
    m_pVertexDataBuffer->setData(vertexBufferData);
    m_pNormalDataBuffer->setData(normalBufferData);
    m_pColorDataBuffer->setData(colorBufferData);
    m_pIndexDataBuffer->setData(indexBufferData);

    // Attributes
    Qt3DRender::QAttribute *positionAttribute = new Qt3DRender::QAttribute();
    positionAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
    positionAttribute->setBuffer(m_pVertexDataBuffer);
   // positionAttribute->setBuffer(m_pVertexDataBuffer.data());
    positionAttribute->setDataType(Qt3DRender::QAttribute::Float);
    positionAttribute->setDataSize(3);
    positionAttribute->setByteOffset(0);
    positionAttribute->setByteStride(3 * sizeof(float));
    positionAttribute->setCount(vertices.length());
    positionAttribute->setName(Qt3DRender::QAttribute::defaultPositionAttributeName());

    Qt3DRender::QAttribute *normalAttribute = new Qt3DRender::QAttribute();
    normalAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
    normalAttribute->setBuffer(m_pNormalDataBuffer);
    //normalAttribute->setBuffer(m_pNormalDataBuffer.data());
    normalAttribute->setDataType(Qt3DRender::QAttribute::Float);
    normalAttribute->setDataSize(3);
    normalAttribute->setByteOffset(0);
    normalAttribute->setByteStride(3 * sizeof(float));
    normalAttribute->setCount(vertices.length());
    normalAttribute->setName(Qt3DRender::QAttribute::defaultNormalAttributeName());

    Qt3DRender::QAttribute* colorAttribute = new Qt3DRender::QAttribute();
    colorAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
    colorAttribute->setBuffer(m_pColorDataBuffer);
    //colorAttribute->setBuffer(m_pColorDataBuffer.data());
    colorAttribute->setDataType(Qt3DRender::QAttribute::Float);
    colorAttribute->setDataSize(3);
    colorAttribute->setByteOffset(0);
    colorAttribute->setByteStride(3 * sizeof(float));
    colorAttribute->setCount(vertices.length());
    colorAttribute->setName(Qt3DRender::QAttribute::defaultColorAttributeName());

    Qt3DRender::QAttribute *indexAttribute = new Qt3DRender::QAttribute();
    indexAttribute->setAttributeType(Qt3DRender::QAttribute::IndexAttribute);
    indexAttribute->setBuffer(m_pIndexDataBuffer);
    //indexAttribute->setBuffer(m_pIndexDataBuffer.data());
    indexAttribute->setDataType(Qt3DRender::QAttribute::UnsignedInt);
    indexAttribute->setDataSize(3);
    indexAttribute->setByteOffset(0);
    indexAttribute->setByteStride(3 * sizeof(uint));
    indexAttribute->setCount(face_normals.length());

    customGeometry->addAttribute(positionAttribute);
    customGeometry->addAttribute(normalAttribute);
    /*customGeometry->addAttribute(colorAttribute);*/
    customGeometry->addAttribute(indexAttribute);

    //Set the final geometry and primitive type
    customMeshRenderer->setPrimitiveType(Qt3DRender::QGeometryRenderer::Triangles);
    customMeshRenderer->setVerticesPerPatch(3);
    customMeshRenderer->setGeometry(customGeometry);


    customMeshRenderer->setVertexCount(faces_idx.length()*3);

    customMeshEntity->addComponent(customMeshRenderer);
    customMeshEntity->addComponent(transform);

    setMaterial(customMeshEntity);

    return rootEntity;
}

訪問幀緩沖區的最佳方法是什么？還是有其他方法來獲取網格物體的快照？

我最后的希望是自己實現渲染管道（至少從投射的坐標到像素坐標），但我更喜歡另一種解決方案。 不幸的是我不得不依賴Qt3D並且無法切換到其他類如QOpenGLWidget。 至少我還沒有找到整合它的可能性。

我是Qt3D的新手，缺乏詳細的文檔並沒有讓它變得更容易。

Answer 1

您可以使用QRenderCapture 。 這基本上為你做了一個glReadPixels 。 這個文檔有點稀疏，但在線有一個例子 。

或者，我實現了一個離線渲染器 ，如果您不想要一個完整的3D窗口，它可以幫助您。

我不確定你的意思

計算3D網格的像素坐標（例如，制作快照）以從特定的攝像機角度找到該網格的2D形狀

但是如果你想要只用一種顏色（沒有高光）渲染整個網格，你可以嘗試QPerVertexColorMaterial ，它給了我完全相同的結果。