SilverScreen Solid Modeler

Edges and Vertices

Edges and Vertices

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Edges and Vertices

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SilverScreenAPI

 

Edges and Vertices

 

 

Vertices

Each object in SilverScreen has a set of vertices. Each vertex in the set may be addressed by its vertex number. For an object that has n vertices, the range of vertex numbers is 1 through n.

 

For a given object and a given vertex number, the function xyz_of_vertex returns a pointer to the xyz-coordinate associated with that vertex. The following will display the coordinates of all vertices in the object obj:

 

C / C++ Code

 

 OBJECT_NODE *obj;

 int i;

 

 for ( i = 1 ; i <= obj->vertices ; i++ )

    ss_command ( "note vertex: %d  %z", i, xyz_of_vertex (obj,i) );

 

 

 

Edges

Each object also has a set of edges. Each edge is addressable with an edge number, and is associated with two vertex numbers.

 

For a given object and a given edge number, the function vertex1_of_edge will return the vertex number of the first vertex, while vertex2_of_edge will return the vertex number of the second. The following displays the vertex numbers of all edges in obj:

 

C / C++ Code

 

 for ( i = 1 ; i <= obj->edges ; i++ )

    ss_command ( "note edge: %d  %z %z",
                i,
                vertex1_of_edge (obj,i),
                vertex2_of_edge (obj,i) );

 

 

For obj, the addresses of the coordinates of the vertices of edge i can be expressed as:

 

C / C++ Code

 

 xyz_of_vertex (vertex1_of_edge (obj,i));

 xyz_of_vertex (vertex2_of_edge (obj,i));

 

 

However, two additional functions, xyz1_of_edge and xyz2_of_edge, allow simpler expressions that are equivalent to those shown above:

 

C / C++ Code

 

 xyz1_of_edge ( obj, i );

 xyz2_of_edge ( obj, i );

 

 

The following can thus be used to display the coordinates of the edges of obj:

 

C / C++ Code

 

 for ( i = 1 ; i <= obj->edges ; i++ )

    ss_command ( "note edge: %d %z %z", i,

                  xyz1_of_edge ( obj, i ),
                  xyz2_of_edge ( obj, i ) );

 

 

 

Primitive Structures

The structures of the point, line and round (circle/arc) nodes are shown below:

 

C / C++ Code

 

 POINT_NODE
    {
    // Common PRIM_NODE section omitted.

    VERTEX      point;
    int         point_type;
    USINT       point_width_style;
    double      point_size;
    RGB         point_rgb;
    };

 

 

 

C / C++ Code

 

 LINE_NODE
    {
    // Common PRIM_NODE section omitted.

    EDGE        edge;
    };

 

 

 

C / C++ Code

 

 ROUND_NODE
    {
    // Common PRIM_NODE section omitted.

    XYZ            horizontal;
    XYZ            vertical;
    double         start_angle;
    double         stop_angle;
    SURFACE_NODE   *sn;
    RGB            surface_rgb;
    RGB            round_rgb;
    int            surface_pattern_number;
    USINT          round_width_style;
    VERTEX         center;
    int            round_type;
    TEXTURE_DATA   *texture;
    };

 

 

Each of these primitives uses references to the edge and vertex lists. LINE_NODE has an edge number that can be used to retrieve the endpoints of the line. POINT_NODE and ROUND_NODE have vertex numbers that can be used to retrieve the coordinate of a point. We give several examples.

 

LINE_NODE contains an edge number edge. For LINE_NODE *p , the addresses of endpoints of p are given by the expressions:

 

C / C++ Code

 

 xyz1_of_edge ( p->parent, p->edge );

 xyz2_of_edge ( p->parent, p->edge );

 

 

The ROUND_NODE contains a vertex number center. For ROUND_NODE *r , the address of the center coordinate is given by:

 

C / C++ Code

 

 xyz_of_vertex ( r->parent, r->center );

 

 

 

In both cases above, note that r->parent is a pointer to the OBJECT_NODE that contains p.

 

Note: The distributed sample program lister.c , which lists the components of a SilverScreen drawing, provides a guide to navigating the drawing data structure.