add qt6 support

FileHeightFieldImage.cc

@@ -176,8 +176,8 @@ void FileHeightFieldPNGPlugin::loadImageAsTriangleMesh(QImage& _image,TriMesh* _
   for ( int i = _minX ; i < _maxX ; ++i ) {
     for ( int j = _minY ; j < _maxY ; ++j ) {
       const QColor currentColor = _image.pixel(i,j);
-      double value = std::max(currentColor.redF(),currentColor.blueF());
-      value = std::max(currentColor.greenF(),value);
+      float value = std::max((float)currentColor.redF(),(float)currentColor.blueF());
+      value = std::max((float)currentColor.greenF(),value);
       TriMesh::VertexHandle vh = _mesh->add_vertex(TriMesh::Point(i,j,-value * _height));
       _mesh->set_color(vh,TriMesh::Color(currentColor.redF(),currentColor.greenF(),currentColor.blueF(),1.0f));
     }