I create a Qt3D mesh like this:
Qt3DCore::QEntity *newEntity = new Qt3DCore::QEntity(); Qt3DExtras::QConeMesh *mesh =new Qt3DExtras::QConeMesh(); mesh->setTopRadius(0.2); mesh->setBottomRadius(1.0); mesh->setLength(2.0); for(int i = 0; i < mesh->geometry()->attributes().size(); ++i) { mesh->geometry()->attributes().at(i)->buffer()->setSyncData(true); // To have access to data } newEntity->addComponent(mesh); The created mesh looks like this:
Later in the code, I try to export the above mesh in STL binary format. To do so, I extract the geometry and transformation components of the entity:
Qt3DCore::QComponent *compoMesh = nullptr; // place holder for mesh geometry of entity Qt3DCore::QComponent *compoTran = nullptr; // place holder for mesh transformation of entity QVector<Qt3DCore::QComponent *> compos = newEntity->components(); for(int i = 0; i < compos.size(); ++i) { if (qobject_cast<Qt3DRender::QGeometryRenderer *>(compos.at(i))) { compoMesh = compos.at(i); // mesh geometry component } else if (qobject_cast<Qt3DCore::QTransform *>(compos.at(i))) { compoTran = compos.at(i); // mesh transformation component } } Then I get the buffer data containing the vertex positions and normals:
Qt3DRender::QGeometryRenderer *mesh = qobject_cast<Qt3DRender::QGeometryRenderer *>(compoMesh); Qt3DRender::QGeometry *geometry = mesh->geometry(); QVector<Qt3DRender::QAttribute *> atts = geometry->attributes(); Now, we focus on vertex positions attribute and vertex normals attribute. We get the byte offset and byte stride for each, also we check if both are using the same data buffer:
for(int i = 0; i < atts.size(); ++i) { if(atts.at(i)->name() == Qt3DRender::QAttribute::defaultPositionAttributeName()) { byteOffsetPos = atts.at(i)->byteOffset(); byteStridePos = atts.at(i)->byteStride(); bufferPtrPos = atts.at(i)->buffer(); } else if(atts.at(i)->name() == Qt3DRender::QAttribute::defaultNormalAttributeName()) { byteOffsetNorm = atts.at(i)->byteOffset(); byteStrideNorm = atts.at(i)->byteStride(); bufferPtrNorm = atts.at(i)->buffer(); } } if(bufferPtrPos != bufferPtrNorm) { qDebug() << __func__ << "!!! Buffer pointer for position and normal are NOT the same"; // Throw error here } Then I use the byte offset and byte stride to extract triangles and write them to STL file. However the exported STL is NOT good:
I use the same code for exporting STL of custom meshes which works fine. However when I use the same code to export the Qt3D ready-made meshes like QConeMesh, the exported STL is NOT acceptable. Can anybody give me a hint.
UPDATE
As noted by @vre I'm going to post the rest of the code for writing triangles to STL file. It's a large code, I try my best to keep it clear and concise:
For getting triangle positions and normals, I loop over attributes and get the VertexBuffer buffer which stores all the positions and normals:
// I loop over attributes to get access to VertexBuffer buffer for(int i = 0; i < atts.size(); ++i) { Qt3DRender::QBuffer *buffer = atts.at(i)->buffer(); QByteArray data = buffer->data(); // We focus on VertexBuffer, NOT IndexBuffer! if( buffer->type() == Qt3DRender::QBuffer::VertexBuffer ) { // Number of triangles is number of vertices divided by 3: quint32 trianglesCount = atts.at(i)->count() / 3; // For each triangle, extract vertex positions and normals for(int j = 0; j < trianglesCount; ++j) { // Index for each triangle positions data // Each triangle has 3 vertices, hence 3 factor: // We already know byte-offset and byte-stride for positions int idxPos = byteOffsetPos + j * 3 * byteStridePos ; // Index for each triangle normals data // Each tirangle has 3 normals (right?), hence 3 factor: // We already know byte-offset and byte-stride for normals int idxNorm = byteOffsetNorm + j * 3 * byteStrideNorm; // Get x, y, z positions for 1st vertex // I have already checked that attribute base type is float by: `atts.at(i)->vertexBaseType();` QByteArray pos0x = data.mid(idxPos + 0 * sizeof(float), sizeof(float)); QByteArray pos0y = data.mid(idxPos + 1 * sizeof(float), sizeof(float)); QByteArray pos0z = data.mid(idxPos + 2 * sizeof(float), sizeof(float)); // Get x, y z for 1st normal QByteArray norm0x= data.mid(idxNorm + 0 * sizeof(float), sizeof(float)); QByteArray norm0y= data.mid(idxNorm + 1 * sizeof(float), sizeof(float)); QByteArray norm0z= data.mid(idxNorm + 2 * sizeof(float), sizeof(float)); // Get x, y, z positions for 2nd vertex QByteArray pos1x = data.mid(idxPos + 1 * byteStridePos + 0 * sizeof(float), sizeof(float)); QByteArray pos1y = data.mid(idxPos + 1 * byteStridePos + 1 * sizeof(float), sizeof(float)); QByteArray pos1z = data.mid(idxPos + 1 * byteStridePos + 2 * sizeof(float), sizeof(float)); // Get x, y, z for 2nd normal QByteArray norm1x= data.mid(idxNorm + 1 * byteStrideNorm + 0 * sizeof(float), sizeof(float)); QByteArray norm1y= data.mid(idxNorm + 1 * byteStrideNorm + 1 * sizeof(float), sizeof(float)); QByteArray norm1z= data.mid(idxNorm + 1 * byteStrideNorm + 2 * sizeof(float), sizeof(float)); // Get x, y, z positions for 3rd vertex QByteArray pos2x = data.mid(idxPos + 2 * byteStridePos + 0 * sizeof(float), sizeof(float)); QByteArray pos2y = data.mid(idxPos + 2 * byteStridePos + 1 * sizeof(float), sizeof(float)); QByteArray pos2z = data.mid(idxPos + 2 * byteStridePos + 2 * sizeof(float), sizeof(float)); // Get x, y, z for 3rd normal QByteArray norm2x= data.mid(idxNorm + 2 * byteStrideNorm+ 0 * sizeof(float), sizeof(float)); QByteArray norm2y= data.mid(idxNorm + 2 * byteStrideNorm+ 1 * sizeof(float), sizeof(float)); QByteArray norm2z= data.mid(idxNorm + 2 * byteStrideNorm+ 2 * sizeof(float), sizeof(float)); // Convert x, y, z byte arrays into floats float floatPos0x; if ( pos0x.size() >= sizeof(floatPos0x) ) { floatPos0x = *reinterpret_cast<const float *>( pos0x.data() ); } float floatPos0y; if ( pos0y.size() >= sizeof(floatPos0y) ) { floatPos0y = *reinterpret_cast<const float *>( pos0y.data() ); } float floatPos0z; if ( pos0z.size() >= sizeof(floatPos0z) ) { floatPos0z = *reinterpret_cast<const float *>( pos0z.data() ); } // Do the rest of byte-array to float conversions: // norm0x=>floatNorm0x, norm0y=>floatNorm0y, norm0z=>floatNorm0z // pos1x=>floatPos1x, pos1y=>floatPos1y, pos1z=>floatPos1z // norm1x=>floatNorm1x, norm1y=>floatNorm1y, norm1z=>floatNorm1z // pos2x=>floatPos2x, pos2y=>floatPos2y, pos2z=>floatPos2z // norm2x=>floatNorm2x, norm2y=>floatNorm2y, norm2z=>floatNorm2z // Compose positions matrix before applying transformations // I'm going to use `QMatrix4x4` but I have 3 vertices of 3x1 // Therefore I have to fill out `QMatrix4x4` with zeros and ones // Please see this question and its answer: https://stackoverflow.com/q/51979168/3405291 QMatrix4x4 floatPos4x4 = QMatrix4x4( floatPos0x, floatPos1x, floatPos2x, 0, floatPos0y, floatPos1y, floatPos2y, 0, floatPos0z, floatPos1z, floatPos2z, 0, 1 , 1 , 1 , 0 ); // Apply transformations to positions: // We already have transformations component `compoTran` from previous code: Qt3DCore::QTransform *tran = qobject_cast<Qt3DCore::QTransform *>(compoTran); QMatrix4x4 newFloatPos4x4 = tran->matrix() * floatPos4x4; // Get new positions after applying transformations: float newFloatPos0x = newFloatPos4x4(0,0); float newFloatPos0y = newFloatPos4x4(1,0); float newFloatPos0z = newFloatPos4x4(2,0); float newFloatPos1x = newFloatPos4x4(0,1); float newFloatPos1y = newFloatPos4x4(1,1); float newFloatPos1z = newFloatPos4x4(2,1); float newFloatPos2x = newFloatPos4x4(0,2); float newFloatPos2y = newFloatPos4x4(1,2); float newFloatPos2z = newFloatPos4x4(2,2); // Convert all the floats (after applying transformations) back to byte array: QByteArray newPos0x( reinterpret_cast<const char *>( &newFloatPos0x ), sizeof( newFloatPos0x ) ); QByteArray newPos0y( reinterpret_cast<const char *>( &newFloatPos0y ), sizeof( newFloatPos0y ) ); QByteArray newPos0z( reinterpret_cast<const char *>( &newFloatPos0z ), sizeof( newFloatPos0z ) ); QByteArray newPos1x( reinterpret_cast<const char *>( &newFloatPos1x ), sizeof( newFloatPos1x ) ); QByteArray newPos1y( reinterpret_cast<const char *>( &newFloatPos1y ), sizeof( newFloatPos1y ) ); QByteArray newPos1z( reinterpret_cast<const char *>( &newFloatPos1z ), sizeof( newFloatPos1z ) ); QByteArray newPos2x( reinterpret_cast<const char *>( &newFloatPos2x ), sizeof( newFloatPos2x ) ); QByteArray newPos2y( reinterpret_cast<const char *>( &newFloatPos2y ), sizeof( newFloatPos2y ) ); QByteArray newPos2z( reinterpret_cast<const char *>( &newFloatPos2z ), sizeof( newFloatPos2z ) ); // Log triangle vertex positions and normals (float numbers) // A sample log is posted on this question on StackOverflow qDebug() << __func__ << " pos 0: x " << newFloatPos0x << " y " << newFloatPos0y << " z " << newFloatPos0z; qDebug() << __func__ << " pos 1: x " << newFloatPos1x << " y " << newFloatPos1y << " z " << newFloatPos1z; qDebug() << __func__ << " pos 2: x " << newFloatPos2x << " y " << newFloatPos2y << " z " << newFloatPos2z; qDebug() << __func__ << " norm 0: x " << floatNorm0x << " y " << floatNorm0y << " z " << floatNorm0z; qDebug() << __func__ << " norm 1: x " << floatNorm1x << " y " << floatNorm1y << " z " << floatNorm1z; qDebug() << __func__ << " norm 2: x " << floatNorm2x << " y " << floatNorm2y << " z " << floatNorm2z; // Write the triangle to STL file // Note that STL file needs a header which is written in another section of code // Note that STL file needs total number of triangles which is written in another section of code // Note that STL file needs only one normal vector for each triangle, but here we have 3 normals (for 3 vertices), therefore I'm writing only the 1st normal to STL (is it OK?!) // `baStl` is a byte-array containing all the STL data // `baStl` byte-array is written to a file in another section of the code QBuffer tempBuffer(&baStl); tempBuffer.open(QIODevice::Append); tempBuffer.write( norm0x ); // vertex 0 Normal vector tempBuffer.write( norm0y ); tempBuffer.write( norm0z ); tempBuffer.write( newPos0x ); // New vertex 0 position tempBuffer.write( newPos0y ); tempBuffer.write( newPos0z ); tempBuffer.write( newPos1x ); // New vertex 1 position tempBuffer.write( newPos1y ); tempBuffer.write( newPos1z ); tempBuffer.write( newPos2x ); // New vertex 2 position tempBuffer.write( newPos2y ); tempBuffer.write( newPos2z ); tempBuffer.write("aa"); // Attribute byte count: UINT16: 2 bytes: content doesn't matter, just write 2 bytes tempBuffer.close(); } } } The above code works perfect for custom meshes. I mean when I import a STL file into my Qt3D application and then export it again as STL, the exported STL is good. The problem is: when creating Qt3D ready-made meshes like QConeMesh, the exported STL is screwed up, I mean the overall geometry is OK, but the triangles are messed up as shown in the above image.
My code logs following values when trying to export a QConeMesh. As can be seen, normal vectors have unit size which shows they are actually normals:
... exportStlUtil pos 0: x -10.6902 y -7.55854 z 4.76837e-07 exportStlUtil pos 1: x -12.8579 y -4.31431 z 2.98023e-07 exportStlUtil pos 2: x -13.6191 y -0.487476 z 5.96046e-08 exportStlUtil norm 0: x -0.707107 y 0 z 0.707107 exportStlUtil norm 1: x -0.92388 y 0 z 0.382683 exportStlUtil norm 2: x -1 y 0 z -8.74228e-08 exportStlUtil pos 0: x -12.8579 y 3.33936 z -1.19209e-07 exportStlUtil pos 1: x -10.6902 y 6.58359 z -3.57628e-07 exportStlUtil pos 2: x -7.44594 y 8.75132 z -4.76837e-07 exportStlUtil norm 0: x -0.92388 y 0 z -0.382683 exportStlUtil norm 1: x -0.707107 y 0 z -0.707107 exportStlUtil norm 2: x -0.382683 y 0 z -0.92388 exportStlUtil pos 0: x -3.61911 y 9.51252 z -4.76837e-07 exportStlUtil pos 1: x 0.207723 y 8.75132 z -4.76837e-07 exportStlUtil pos 2: x 3.45196 y 6.58359 z -3.57628e-07 exportStlUtil norm 0: x 1.19249e-08 y 0 z -1 exportStlUtil norm 1: x 0.382684 y 0 z -0.923879 exportStlUtil norm 2: x 0.707107 y 0 z -0.707107 exportStlUtil pos 0: x 5.61968 y 3.33936 z -1.19209e-07 exportStlUtil pos 1: x 6.38089 y -0.487479 z 5.96046e-08 exportStlUtil pos 2: x 6.38089 y -0.487477 z 0.133333 exportStlUtil norm 0: x 0.92388 y 0 z -0.382683 exportStlUtil norm 1: x 1 y 0 z 1.74846e-07 exportStlUtil norm 2: x 1 y 0 z 0 exportStlUtil pos 0: x 5.61968 y -4.31431 z 0.133334 exportStlUtil pos 1: x 3.45195 y -7.55854 z 0.133334 exportStlUtil pos 2: x 0.207721 y -9.72627 z 0.133334 exportStlUtil norm 0: x 0.92388 y 0 z 0.382683 exportStlUtil norm 1: x 0.707107 y 0 z 0.707107 exportStlUtil norm 2: x 0.382683 y 0 z 0.92388 ...