如何在Qt3D中绘制一条简单的线？

Question

我觉得这应该是非常简单的,但对于我的生活,我无法弄清楚如何使用Qt 3D绘制基本线.我能够在这个主题上找到的唯一指导就是这个不起眼的视频,其中有一些原始字节缓冲区和内存操作通过几乎没有记录的类进行.

有没有更好的方法来使用我缺少的闪亮的新API？

Answer 1

从你链接的视频,我想出了下面的代码(也张贴在Qt的论坛:https://forum.qt.io/topic/66808/qt3d-draw-grid-axis-lines/3).

首先,您需要创建QGeometry.因为它是一条简单的线,它只由2个顶点(起点,终点)和2个索引(链接顶点)组成.为此,您需要创建2个QByteArray并将它们存储到QBuffer中.在第一个中,存储2个顶点(每个顶点的x,y和z坐标).在第二个中,您只是说要将第一个顶点链接到第二个顶点.正如我们Qt3DRender::QGeometryRenderer::Lines在渲染器上使用的那样,只需要2个索引.

完成后,您只需将QGeometry放入QGeometryRenderer中以获得网格,然后将网格放入QEntity中,使其显示在树中并进行渲染.

#include <Qt3DCore/QEntity>
#include <Qt3DCore/QTransform>
#include <Qt3DExtras/QPhongMaterial>
#include <Qt3DRender/QAttribute>
#include <Qt3DRender/QBuffer>
#include <Qt3DRender/QGeometry>

void drawLine(const QVector3D& start, const QVector3D& end, const QColor& color, Qt3DCore::QEntity *_rootEntity)
{
    auto *geometry = new Qt3DRender::QGeometry(_rootEntity);

    // position vertices (start and end)
    QByteArray bufferBytes;
    bufferBytes.resize(3 * 2 * sizeof(float)); // start.x, start.y, start.end + end.x, end.y, end.z
    float *positions = reinterpret_cast<float*>(bufferBytes.data());
    *positions++ = start.x();
    *positions++ = start.y();
    *positions++ = start.z();
    *positions++ = end.x();
    *positions++ = end.y();
    *positions++ = end.z();

    auto *buf = new Qt3DRender::QBuffer(geometry);
    buf->setData(bufferBytes);

    auto *positionAttribute = new Qt3DRender::QAttribute(geometry);
    positionAttribute->setName(Qt3DRender::QAttribute::defaultPositionAttributeName());
    positionAttribute->setVertexBaseType(Qt3DRender::QAttribute::Float);
    positionAttribute->setVertexSize(3);
    positionAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
    positionAttribute->setBuffer(buf);
    positionAttribute->setByteStride(3 * sizeof(float));
    positionAttribute->setCount(2);
    geometry->addAttribute(positionAttribute); // We add the vertices in the geometry

    // connectivity between vertices
    QByteArray indexBytes;
    indexBytes.resize(2 * sizeof(unsigned int)); // start to end
    unsigned int *indices = reinterpret_cast<unsigned int*>(indexBytes.data());
    *indices++ = 0;
    *indices++ = 1;

    auto *indexBuffer = new Qt3DRender::QBuffer(geometry);
    indexBuffer->setData(indexBytes);

    auto *indexAttribute = new Qt3DRender::QAttribute(geometry);
    indexAttribute->setVertexBaseType(Qt3DRender::QAttribute::UnsignedInt);
    indexAttribute->setAttributeType(Qt3DRender::QAttribute::IndexAttribute);
    indexAttribute->setBuffer(indexBuffer);
    indexAttribute->setCount(2);
    geometry->addAttribute(indexAttribute); // We add the indices linking the points in the geometry

    // mesh
    auto *line = new Qt3DRender::QGeometryRenderer(_rootEntity);
    line->setGeometry(geometry);
    line->setPrimitiveType(Qt3DRender::QGeometryRenderer::Lines);
    auto *material = new Qt3DExtras::QPhongMaterial(_rootEntity);
    material->setAmbient(color);

    // entity
    auto *lineEntity = new Qt3DCore::QEntity(_rootEntity);
    lineEntity->addComponent(line);
    lineEntity->addComponent(material);
}