使用Qt3D绘制机械手场景

1.前言

之前是使用Coin3D来绘制机械手场景的【Qt利用Coin3D（OpenInventor）进行3d绘图】。
后来需要在HarmonyOS显示这个机械手模型，但是想要编译Coin3D到HarmonyOS的话，显然太难了。
然后尝试使用OpenGL原生的函数来绘制，但是HarmonyOS对很多函数都不支持，一查，发现HarmonyOS支持OpenglES。那就麻烦了。
最后，一番兜兜转转，还是用回Qt3D吧。

2.效果

效果也还行，但是某些功能还得研究一下。
点、线、面、灯光等各种功能都ok。

3.实现过程

主要是参考了Qt自带的例程以及网上的一些资料。

3.1.场景代码

创建场景、摄像机、灯光等这些基本元素的代码，是参考Qt自带的例程实现的。比如下面的【Qt 3D Simple C++ Example】

3.2.自定义模型的渲染

【Qt3DExample】

3.3.绘制直线或者网格

【how-do-i-draw-a-simple-line-in-Qt3D】

int drawOriginGrid(const int rows,const int cols,const float step,const QColor& color,Qt3DCore::QEntity *_rootEntity)
{auto *geometry = new Qt3DRender::QGeometry(_rootEntity);QList<QVector3D> vertexList;// 横线for(int i = -rows; i <= rows; i++){vertexList << QVector3D(cols  * step, 0, i * step);vertexList << QVector3D(-cols * step, 0, i * step);}// 竖线for(int i = -cols; i <= cols; i++){vertexList << QVector3D(i * step, 0, rows * step);vertexList << QVector3D(i * step, 0, -rows * step);}QByteArray bufferBytes;bufferBytes.resize(3 * vertexList.length() * sizeof(float));float *positions = reinterpret_cast<float*>(bufferBytes.data());for(int i = 0; i < vertexList.length(); i++){QVector3D vertex = vertexList.at(i);*positions++ = vertex.x();*positions++ = vertex.y();*positions++ = vertex.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(vertexList.length());geometry->addAttribute(positionAttribute); // We add the vertices in the geometry// connectivity between verticesQByteArray indexBytes;indexBytes.resize(2 * vertexList.length() * sizeof(unsigned int));unsigned int *indices = reinterpret_cast<unsigned int*>(indexBytes.data());for(int i = 0; i < vertexList.length(); i++){*indices++ = i;}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(vertexList.length());geometry->addAttribute(indexAttribute); // We add the indices linking the points in the geometry// meshauto *line = new Qt3DRender::QGeometryRenderer(_rootEntity);line->setGeometry(geometry);line->setPrimitiveType(Qt3DRender::QGeometryRenderer::Lines);auto *material = new Qt3DExtras::QPhongMaterial(_rootEntity);material->setAmbient(color);material->setDiffuse(color);// entityauto *lineEntity = new Qt3DCore::QEntity(_rootEntity);lineEntity->addComponent(line);lineEntity->addComponent(material);return 0;
}

4.有待解决的一些问题

4.1.线宽的设置、背面消隐（culling）的设置

有资料说可以通过QRenderStateSet来设置，但是我设置了并没有得到有效的效果

    Qt3DExtras::Qt3DWindow *view = new Qt3DExtras::Qt3DWindow();view->defaultFrameGraph()->setClearColor(QColor(QRgb(0x2b2b2b)));if(0){using namespace Qt3DRender;qDebug() << "frameGraph:" << view->defaultFrameGraph() << view->activeFrameGraph();Qt3DRender::QRenderSurfaceSelector *surSel;auto childNodeList = view->activeFrameGraph()->childNodes();foreach (Qt3DCore::QNode * childNode, childNodeList) {qDebug() << "child:" << childNode;if(qobject_cast<Qt3DRender::QRenderSurfaceSelector*>(childNode)){surSel = qobject_cast<Qt3DRender::QRenderSurfaceSelector*>(childNode);}}qDebug() << surSel->childNodes() << surSel->childNodes()[0]->childNodes()<< surSel->childNodes()[0]->childNodes()[0]->childNodes();qDebug() << surSel->childNodes()[0]->childNodes()[0]->childNodes()[0];((Qt3DRender::QClearBuffers*)(surSel->childNodes()[0]->childNodes()[0]->childNodes()[0]))->setBuffers(QClearBuffers::ColorDepthBuffer);QRenderStateSet *renderStateSet = new QRenderStateSet(surSel->childNodes()[0]->childNodes()[0]);QCullFace *cullFace = new QCullFace();cullFace->setMode(QCullFace::NoCulling);// renderStateSet->addRenderState(cullFace);QLineWidth *lineWidth = new QLineWidth();lineWidth->setValue(100);// renderStateSet->addRenderState(lineWidth);QPointSize *ptSize = new QPointSize();ptSize->setValue(100);// renderStateSet->addRenderState(ptSize);qDebug() << surSel->childNodes()[0]->childNodes()[0]->childNodes();}

4.2.法线的问题

目前好像是支持点法线，不支持面法线，假如使用index模式来渲染面片时，会渲染出奇怪的效果