tutorial_05.docu 3.98 KB
 Jan Möbius committed Feb 06, 2009 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 /** \page tutorial_05 Using standard properties This example shows: - How to add and remove a standard property, - How to get and set the value of a standard property. As we already have seen, we can bind additional data to the mesh entities by means of properties. %OpenMesh provides a set of so-called standard properties. Unlike the custom properties these have some special features and a different interface, which are the matter in this tutorial. The following table lists all available standard properties and the suitable entity for which it can be used.
To add a standard property to an entity simply use the appropriate request method, e.g. \c  request_face_normal(). The only exception is the position (*). It cannot be added because it is permanently available, hence it cannot be removed as well. In this example we -# add vertex normals to a mesh object -# load a file -# check if the file provides vertex normals and calculate them if not -# move every vertex one unit length along its normal direction -# print the resulting positions to std::cout Let's start with adding vertex normals to the mesh: \dontinclude 05-std_properties/properties.cc \skipline request_vertex_normals In a similar manner we can request the other standard properties. For example the face normals: \skipline request_face_normals We need them to calculate the vertex normals with \c update_normals(), if the file didn't provide any. But we can do more with standard properties. We can verify if the mesh has already the property vertex normals \dontinclude 05-std_properties/properties.cc \skipline has_vertex_normals \until } And after usage we remove them again \skipline release_vertex_normals But, what happens if for example the vertex status property has been requested twice? Then the first release does nothing, but the second one will remove it. The standard properties have a reference counter, which is incremented by one for each request and decremented by one for each release. If the counter reaches 0 the property will be removed from memory. Now we know how to add and remove standard properties, but how do we access them? Again we need the mesh object. Unlike the custom properties, where we accessed one with the mesh member function \c property(), for each standard property the mesh provides a get and a set method. We have used one pair of get/set methods already in the previous three tutorials, where we computed a new location for the vertex position. Here we move all vertices a unit length along their normal direction: \dontinclude 05-std_properties/properties.cc \skipline MyMesh::VertexIter \until { \skipline mesh.set_point \skipline } The get-methods take an entity handle and return the value of the desired property, and the set-methods require an additional parameter to pass the new value to the property. According to the table not every pair of get/set-methods apply to every entity. For example a face has normally no texture coordinates, hence a call to \c mesh.texcoord( _face_handle ) will result in an error when compiling the code. Since we know how to add/remove/access standard properties, one further question remains. What data types do they have? And are there more hidden secrets? The next tutorial (\ref tutorial_06) will give the answer. The complete source looks like this: \include 05-std_properties/properties.cc */