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

Software Design3.7. DataAccess NodeThe parameter length defines the number of items inside the virtual array. Figure3.12 sketches a real array of length 12 and a virtual array of length 6. The multipleblock virtual array defines several successive block were each block has a constant size.The constant size of the blocks is addressed as increment. The range of the virtual indexis [0..5]. Inside of each block a constant number of successive items are accessedand the corresponding attribute is repeat. In figure 3.12 these items are colored blue.Figure 3.12: CashFlow: Multiple Block Virtual Array: Several successive blocks are reorganized as avirtual array. Attributes are the offset the number of blocks, the size per block and the number of valuesread per block.To compute the real index from the virtual index a division or modulo operation isneeded. Thus iterators are useful and random access to a virtual index is more expensiveto compute compared with the single block virtual array. The difference betweenthe virtual index and the real index increases while the virtual index increases. If theparameters increment and repeat are the same, the multiple block degenerates to a singleblock virtual array. This should be avoided and the single block virtual array shouldbe used, because of its better performance.Random Virtual ArrayFigure 3.13: CashFlow: Random Virtual Array: Random fields of the original array create the virtualarray. Attributes are a list of indices providing information on the random mapping.The random virtual array requires one additional array of attributes.• look–up tableEach virtual index is mapped to one real index. Even more than one virtual indexmay point to the same real index. Accordingly the number of items in the lookup56