CashFlow, A Visualization Framework for 3D Flow - Studierstube ...

Software Design3.7. DataAccess Node3.7.1 Virtual Array Types in CashFlowFor more flexibility three different kinds of virtual arrays are available. Since they actas data filters evaluated at runtime it is important to keep their abilities and weaknessesin mind. Table 3.1 on page 58 gives an overview on the memory consumption and CPUload of each virtual array type. The three different kinds of virtual arrays encapsulatein the DataAccess node are:⋄ Single Block Virtual Array⋄ Multiple Block Virtual Array⋄ Random Virtual ArrayEach of the three types has its own iterator. All iterators use the same interface.The following attributes are used for all virtual arrays:• lengthNumber of items inside the virtual array.• offsetNumber of items from the first item in the real array to the first item in the virtualarray. Possible values are in the range [0..(real array length-1)].• keyA unique string used to refer to the real data array, which is stored in a MultiDatanode.Additional attributes at runtime used by iterators:– indexPosition in the virtual array used by iterators at runtime.Possible values are in the range [0..(length-1)].– real indexThe index in the real array is computed either from the index in the virtual arrayor is returned from the iterator.Single Block Virtual ArrayThis iterator is very simple. It defines a block of successive values as a new virtualarray shown in figure 3.11. The length of the virtual array is equal to the length ofthe block of the real array. The real index can be computed by adding the offset tothe virtual index. The range of the virtual index is [0..5]. The difference between thevirtual index and the real index is constant while the virtual index increases.54