I need to draw a polygon with Qt3D, but i found how i can do this with triangles. So. I found a code, that works more tightly with OpenGL from Qt3D. It was drawing the line but i changed one to draw triangles. When i set setPrimitiveType(Qt3DRender::QGeometryRenderer::TriangleStrip);, then it works. But i wanna use
setPrimitiveType(Qt3DRender::QGeometryRenderer::Triangles);, that don't work for some reason and don't draw anything. Maybe i did wrong configuration of vertex and index attributes? Or maybe i use incorrect input? (Example of my input is in the bottom)
void MainWindow::drawTriangles(const QPolygonF polygon, QColor color, Qt3DCore::QEntity *_rootEntity)
{
int numOfVertices = polygon.size();
auto *geometry = new Qt3DRender::QGeometry(_rootEntity);
// Create and fill vertex buffer
QByteArray bufferBytes;
bufferBytes.resize(3 * numOfVertices * static_cast<int>(sizeof(float)));
float *positions = reinterpret_cast<float*>(bufferBytes.data());
for(auto point : polygon){
float fHalfMapWidth = (dFittedMaxMapX_ - dFittedMinMapX_) / 2;
float fHalfMapHeight = (dFittedMaxMapY_ - dFittedMinMapY_) / 2;
*positions++ = static_cast<float>(point.x() - (dFittedMinMapX_ + fHalfMapWidth));
*positions++ = 0.0f; //We need to drow only on the surface
*positions++ = static_cast<float>(point.y() - (dFittedMinMapY_ + fHalfMapHeight));
}
auto *buf = new Qt3DRender::QBuffer(geometry);
buf->setData(bufferBytes);
auto *positionAttribute = new Qt3DRender::QAttribute(geometry); // Create a vertex attribute
positionAttribute->setName(Qt3DRender::QAttribute::defaultPositionAttributeName());
positionAttribute->setVertexBaseType(Qt3DRender::QAttribute::Float); // In vertex buffer we store floats
positionAttribute->setVertexSize(3); // Size of a vertex
positionAttribute->setAttributeType(Qt3DRender::QAttribute::VertexAttribute); // Type of an attribute
positionAttribute->setBuffer(buf); // Set vertex buffer
positionAttribute->setByteStride(3 * sizeof(float)); // Stride between vertices
geometry->addAttribute(positionAttribute); // Add the attribute in our Qt3DRender::QGeometry
// Create and fill an index buffer
QByteArray indexBytes;
indexBytes.resize(numOfVertices * static_cast<int>(sizeof(unsigned int))); // start to end
unsigned int *indices = reinterpret_cast<unsigned int*>(indexBytes.data());
for(unsigned int i = 0; i < static_cast<unsigned int>(numOfVertices); ++i) {
*indices++ = i;
}
auto *indexBuffer = new Qt3DRender::QBuffer(geometry);
indexBuffer->setData(indexBytes);
auto *indexAttribute = new Qt3DRender::QAttribute(geometry); // Create an index attribute
indexAttribute->setVertexBaseType(Qt3DRender::QAttribute::UnsignedInt); // In the index buffer we will store Unsigned int
indexAttribute->setAttributeType(Qt3DRender::QAttribute::IndexAttribute); // Type of an attribute
indexAttribute->setBuffer(indexBuffer); // Set the index buffer
indexAttribute->setCount(static_cast<unsigned int>(numOfVertices)); // As i understand, this is a number of vertices
geometry->addAttribute(indexAttribute); // Add attribute in our Qt3DRender::QGeometry
auto *poly = new Qt3DRender::QGeometryRenderer(_rootEntity);
poly->setGeometry(geometry);
//poly->setPrimitiveType(Qt3DRender::QGeometryRenderer::TriangleStrip); - Working variant
poly->setPrimitiveType(Qt3DRender::QGeometryRenderer::Triangles); // - This is not working variant
//Create a material
auto *material = new Qt3DExtras::QPhongMaterial(_rootEntity);
material->setAmbient(color);
auto *trianglesEntity = new Qt3DCore::QEntity(_rootEntity);
trianglesEntity->addComponent(poly); // Add our primitives
trianglesEntity->addComponent(material); // Add material
}
I tried to use three and four points. When i use 4 points, then it draws if i set primitive type to "TriangleStrip". But with "Triangles" It's don't work in both cases.
mapBorder << QPointF(300,200) << QPointF(100,200) << QPointF(200,0) << QPointF(300,200) << QPointF(200,0) << QPointF(500,200) << QPointF(500,300);
drawTriangles(mapBorder, QColor(Qt::black), mapEntity_);
Or can you to give me another suggestion how to draw polygon or triangle.
