Overview

In this sections the tools that are helpfull for extracting data are presented. Although the context is to write display methods the tools are also usefull for calculating error estimators, norms of functions and for many other purposes.

There are exceptions, but most display methods extract the necessary data in the following way: The hierachical tree is traversed via the interface functions and on any leaf the data are fetched, calculated and rendered. As hanging nodes may occur in an adaptive traverse, hierachical projection is needed to assure continuity.

To support this, there are functions in GRAPE - namely g_traverse_hmesh2d() and g_traverse_hmesh3d() - that implement such an traverse. Among other things these routines need three call-back-functions as arguments.

• projection; in this routine the necessary data on the currrent element are collected and if appropriate interpolated.
• test_if_proceed; this functions controlls the traverse. It is decided whether to proceed on the next finer level or to stop on the current element and in the latter case whether to render on the current element or not. The outcome may be based on the projected data or for example on the error estimators included in the HMesh-interface.
• action_on_element; this functions should contain the code for rendering the data on an element.

Further arguments of g_traverse_hmesh2d() are the Hmesh2d object, a pointer to a HM2_GENERAL variable, the traverse mode, the level of interest, an array of pointers to the element data, a pointer to other arbitrary data possibly needed in the action_on_element routine and a mesh element flag.

The traverse mode, an variable of type integer, determines on which elements the action_on_element routine may be called. Possible values are G_LEAVES, G_PREFIX and G_POSTFIX. If the traverse mode is G_LEAVES the action is at most called on a leaf of the hierachical tree. In contrast if the traverse mode is G_PREFIX or G_POSTFIX the action_on_element routine may be called on all elements of the tree. In the case of G_PREFIX the action_on_element routine is called first on the parent element and after that the children are considered. Whereas in the case of G_POSTFIX only after the complete subtree of an element is traversed the action_on_element routine is called on the element itself.

The level of interest is the maximum depth of the hierachical traverse. In most display methods this should be the level of interest stored in the Hmesh2d object. Since this entry can be manipulated by the user via the uif-hm2-project it is not neccessary that display methods have an interactive element controlling it.

The interface functions of the Hmesh2d allow to choose which entries of the HELEMENT2D structure are filled by the interface. In the same way this choice can be made for the whole traverse with the mesh element flag.

Below the exact prototype of the traverse routine is printed. The other arguments are explained in the next section.

void g_traverse_hmesh2d(
 HMESH2D*     hmesh,
 HM2_GENERAL* general,
 int          traverse_mode,
 int          level_of_interest,
 int      (*projection)       (HELEMENT2D*  helement,
                               HM2_GENERAL* general,
                               void*        element_data,
                               void*        parent_data),
 int      (*test_if_proceed)  (HELEMENT2D*  helement,
                               HM2_GENERAL* general,
                               void*        element_data),
 int      (*action_on_element)(HELEMENT2D*  helement,
                               HM2_GENERAL* general,
                               void*        element_data,
                               void*        action_arg),
 void**   element_data,
 void*    action_arg,
 MESH_ELEMENT_FLAGS mesh_element_flag)