See the k3d::selection namespace for details on this data, which is strongly-coupled to the OpenGL selection mechanism. The selection set stores a list of records, where each record stores a hierarchical list of IDs for gprims that are contained within the set. A selection set represents a set membership where gprims (points, edges, polygons, etc) are either inside or outside the set.At the end of the pipeline, the selection state is used by mappers to change how gprims are rendered based on their state (i.e. The state is stored in arrays that are part of the geometric data set, and thus move through the pipeline like any other variable. A selection state is the actual state (selected versus not selected) of a collection of gprims (points, edges, polygons, etc).K-3D makes an explicit distinction between selection state, selection set, and selection operation structures: Pol圜ylinder -> SelectEdgeRings -> ScalePoints -> Actor/MapperĪ key requirement in the above use cases is the ability to combine user interaction with filter-generated selection - whether a filter creates a selection outright or modifies the selection in its outputs, the user should be able to manually "override" the selection without discarding it entirely, and with a minimum of effort. The user interactively deselects some of the selected edges and applies a ScalePoints filter, which only modifies the selected edges, leaving the selection unchanged: User interactively selects an edge on the cylinder, then applies a SelectEdgeRings filter, which expands the selection to include a "ring" of edges around the circumference of the cylinder. PolySphere -> SelectCube -> TranslatePoints ->Actor/Mapper The user then applies a TranslatePoints filter, which only modifies the positions of the selected points, leaving the selection unchanged: User applies a SelectCube filter, which selects all of the points that fall within a three-dimensional bounding box. Pol圜ube -> ConnectVertices -> Actor/Mapper The selection is changed so that the newly-created edges are now selected: User interactively selects two points on a face diagonal and applies a ConnectVertices filter, which splits the face into two triangles. User interactively selects one face of the cube and applies a ExtrudeFaces filter, which extrudes the selected face, leaving the selection unchanged: Because selection is a critical part of the process, it has received a lot of attention. Typically, users tend to go through an iterative process where they begin with a simple geometric source (cube, sphere, cylinder, etc) and add complexity through a set of select/modify/repeat operations. Data tends to be orders of magnitude smaller in some areas - a typical 3D character model using subdivision surfaces or NURBS will number points and elements in the thousands to tens-of-thousands range. The bulk of the functionality revolves around interactive modelling (creation) of 3D datasets, rather than working with existing experimental or simulated data. Of course, there are significant differences, too: K-3D isn't client-server, nor is it parallel. Geometric data can include arbitrary arrays of user-defined data which are equivalent to variables in ParaView. Geometric data moves through the pipeline using a heterogeneous data structure which is roughly comparable to unstructured grids in ParaView. K-3D ( ) is an open-source artists' tool that has some striking similarities to ParaView - in particular, it is based on an implicit, demand-driven pipeline architecture where users make connections between sources, filters, and sinks to manipulate their data.
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