I feel like this should be pretty straightforward, but for my life I can't figure out how to draw a basic line using Qt 3D. The only guidance I've been able to find on the subject is this obscure video, in which there's an off-putting amount of raw byte buffer and memory manipulation going on via scarcely documented classes.
Is there a better way to do this using the shiny new API that I'm missing?
From the video you linked, I came up with the code below (also posted in Qt forums: https://forum.qt.io/topic/66808/qt3d-draw-grid-axis-lines/3).
First, you need to create your QGeometry. As it is a simple line, it is only composed of 2 vertices (start point, end point), and 2 indices (that links the vertices). To do so, you need to create 2 QByteArray and store them into a QBuffer. In the first one, you store the 2 vertices (x, y, and z coordinates for each). In the second, you just say that you want to link your first vertex to the second. As we use Qt3DRender::QGeometryRenderer::Lines
on the renderer, only 2 indices are required.
Once it is done, you just have to put your QGeometry in a QGeometryRenderer to have a mesh, and put the mesh in a QEntity so it appears in the tree and it is rendered.
#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);
}
Here's the correction I had to do on buffer type (I assume its deprecated now), respectively:
auto *buf = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, geometry);
auto *indexBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::IndexBuffer, geometry);
Mine is Qt 5.9 on Win 10.
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