Qt3D: QGeometryData::detach() does not function as expected
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StackOverflow is failing me, so I wondered if anyone here would be able to explain some Qt3D to me:
I'm trying to get my head around how the QGeometryData class works in the Qt3D library. I understand that it encapsulates shared data, but even after calling detach() (whose description is "Force this geometry to ensure it has its own unshared internal data block, making a copy in the case that it is currently shared"), modifications to my original object are reflected in the QGeometryData object when they shouldn't be, as far as I can see.
My process is as follows:
- A RenderBox object (my class) is set up to reside at the origin of the world.
- toGeomData() is called in order to convert the object's data (origin, min/max points) into actual geometry data:
@QGeometryData RenderBox::toGeomData() const
{
// Calculate the min and max co-ordinates in world space.
QVector3D min = m_vecPosition + minimum();
QVector3D max = m_vecPosition + maximum();
QColor colMin = colorMin();
QColor colMax = colorMax();
float colMinR = colMin.redF();
float colMinG = colMin.greenF();
float colMinB = colMin.blueF();
float colMaxR = colMax.redF();
float colMaxG = colMax.greenF();
float colMaxB = colMax.blueF();
QGeometryData geom;// Order of vertices: // 0. Minimum // 1. Minimum with modified X co-ord // 2. Minimum with modified X and Z co-ords // 3. Minimum with modified Z co-ord // 4. Maximum with modified Z co-ord // 5. Maximum with modified Z and X co-ords // 6. Maximum with modified X co-ord // 7. Maximum // This gives us an easy counter-clockwise winding for the top and bottom faces. const QVector3D verts[8] = // Taking Z as "north" and looking down on the box (Y pointing at us), we have: { min, // Lower SE 0 QVector3D(max.x(), min.y(), min.z()), // Lower SW 1 QVector3D(max.x(), min.y(), max.z()), // Lower NW 2 QVector3D(min.x(), min.y(), max.z()), // Lower NE 3 QVector3D(max.x(), max.y(), min.z()), // Upper SW 4 QVector3D(min.x(), max.y(), min.z()), // Upper SE 5 QVector3D(min.x(), max.y(), max.z()), // Upper NE 6 max // Upper NW 7 }; QColor cols[8] = { QColor(0.0, 0.0, 0.0), QColor(0.0, 0.0, 0.0), QColor(0.0, 0.0, 0.0), QColor(0.0, 0.0, 0.0), QColor(0.0, 0.0, 0.0), QColor(0.0, 0.0, 0.0), QColor(0.0, 0.0, 0.0), QColor(0.0, 0.0, 0.0) }; QVector3D dir = (max - min).normalized(); // Set each vertex's colour appropriately. for ( int i = 0; i < 8; i++ ) { float extent = scalarProjection((verts[i]-min).normalized(), dir); //qDebug() << "Extent for" << verts[i] << "=" << extent; cols[i].setRedF(colMinR + (extent * (colMaxR-colMinR))); cols[i].setGreenF(colMinG + (extent * (colMaxG-colMinG))); cols[i].setBlueF(colMinB + (extent * (colMaxB-colMinB))); } // Normals for faces const QVector3D nTop(0, 1, 0); // Up = +Y const QVector3D nBottom(0, -1, 0); // Down = -Y const QVector3D nNorth(0, 0, 1); // North = +Z const QVector3D nSouth(0, 0, -1); // South = -Z const QVector3D nEast(-1, 0, 0); // East = -X const QVector3D nWest(1, 0, 0); // West = +X int n = 0; // Top face geom.appendVertex(verts[4], verts[5], verts[6], verts[7]); geom.appendNormal(nTop, nTop, nTop, nTop); geom.appendColor(cols[4], cols[5], cols[6], cols[7]); geom.appendIndex(n);geom.appendIndex(n+1);geom.appendIndex(n+2); geom.appendIndex(n+2);geom.appendIndex(n+3);geom.appendIndex(n); n += 4; // Bottom face geom.appendVertex(verts[0], verts[1], verts[2], verts[3]); geom.appendNormal(nBottom, nBottom, nBottom, nBottom); geom.appendColor(cols[0], cols[1], cols[2], cols[3]); geom.appendIndex(n);geom.appendIndex(n+1);geom.appendIndex(n+2); geom.appendIndex(n+2);geom.appendIndex(n+3);geom.appendIndex(n); // ...and so on. // Return the GeomData. return geom;}@
- A copy of the QGeometryData is returned.
- detach() is called on the returned copy.
- The RenderBox then has its origin changed from 0, 0, 0 to 2, 2, 2.
- The original QGeometryData, exported before the change, is given to the scene builder; the RenderBox is not.
- When the scene renders, the geometry is present at 2, 2, 2 and not 0, 0, 0 as expected.
Am I interpreting this wrong? Is there a way to export an object (which contains only minimal data, ie. origin and min/max vectors) to geometry data (ie. vertices and normals) and have the geometry data then become completely independent of the object?
Thanks.
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Hi,
Since Qt3D is not yet released, I would recommend asking this question on the "interest":http://lists.qt-project.org/mailman/listinfo/interest mailing list. You'll find there Qt's developers/maintainers (this forum is more user oriented)
