PFA(3g) — Subroutines

Name

PFA − Defines a 2D fill area primitive.

Operating States: PHOP, ∗, STOP, ∗
PHIGS standard function
Creates a structure element

Syntax

PFA (N, PXA, PYA)

Argument     Data Type        Access    Description
---------------------------------------------------------------------------
N            Integer          Read      Number of points
PXA(N),      Array of reals   Read      Coordinates of the points, in
PYA(N)                                  modeling coordinates, that
                                        specify the fill area
---------------------------------------------------------------------------

Description

PFA uses a list of points to define a two-dimensional fill area primitive. Depending on the current edit mode, this function either inserts the new structure element directly after the element indicated by the pointer or replaces the element indicated by the pointer. The pointer then points to the new fill area element.

The PFA function, with its bound attributes, defines a polygon interior in two-dimensional (x and y) form. The polygon may be filled but does not have edges. (Compare this function to the fill area set functions, which define polygon interiors and edges.)

A call to PFA has the following effects during structure traversal:

•Digital PHIGS generates a two-dimensional polygon interior.

•Digital PHIGS closes any unclosed polygon, implicitly.

•Digital PHIGS binds the current values of the fill area interior attributes, as defined in the PHIGS traversal state list, to the fill area primitive.

If Digital PHIGS clips an area, it generates new boundaries for the area as part of the displayed interior. Whether Digital PHIGS actually displays these boundaries depends upon the current HLHSR mode. The PSIR interior style setting (for example, HOLLOW) also affects boundary representation.

The interior of a fill area primitive is defined as follows:

•For a specified point, a straight line is created starting at that point and continuing to infinity.

•If the number of intersections between the straight line and the fill area boundary is odd, the point is within the fill area.

•If the number of intersections between the straight line and the fill area boundary is even, the point is outside the fill area.

•If the straight line passes through a fill area vertex tangentially, the intersection count is not affected.

If Digital PHIGS is in immediate mode, it performs this function immediately, but the function does not create a structure element. If you have information about the shape of the fill area, use the DFAW3 function instead of this function for increased performance.

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PFA(3g) — Subroutines

Name

Syntax

Description

See Also