GSECNV(3g,L)                AIX Technical Reference                GSECNV(3g,L)



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gsecnv



PURPOSE

Converts an ellipse to a polyline.

C SYNTAX

int gsecnv_ (cx, cy, ma, mi, ang, bx, by, ex, ey, rot, len, x, y, pre)

int *cx, *cy, *ma, *mi, *ang, *bx, *by, *ex, *ey, *rot, *len, *x, *y, *pre;

FORTRAN SYNTAX

INTEGER function gsecnv (cx, cy, ma, mi, ang, bx, by, ex, ey, rot,
len, x, y, pre)

INTEGER cx, cy, ma, mi, ang, bx, by, ex, ey, rot, len, x(*), y(*), pre

PASCAL SYNTAX

FUNCTION gsecnv_ (

VAR cx, cy, ma, mi, ang, bx, by, ex, ey, rot, len: INTEGER;
VAR x, y: ARRAY [1..k] of INTEGER;
VAR pre: INTEGER
): INTEGER [PUBLIC];

DESCRIPTION

The gsecnv subroutine converts a counterclockwise elliptical arc definition
into an array of vertices.  The list of vertices can then be used to draw an
elliptical arc with the gspoly subroutine or to fill an elliptical arc with the
gsfply subroutine.  In general, it can be concatenated with other list(s) of
vertices to draw or fill more complex shapes, such as chord arcs, pie arcs, or
rectangles with round corners.  When the beginning and ending points are
identical, the list of vertices contains the full ellipse, which can then
be drawn or filled.

Parameters

cx, cy   Define the coordinates of the center of the ellipse.

ma, mi   Define half of the nonzero major and minor axes of the ellipse.

ang      Defines the off-axis angle of the ellipse.  If ang is 0, the major
         axis is the x-axis and the minor axis is the y-axis.  A positive value
         rotates the ellipse counterclockwise; a negative value rotates it
         clockwise.  All values are in degrees and modulo 360.



Processed November 7, 1990       GSECNV(3g,L)                                 1






GSECNV(3g,L)                AIX Technical Reference                GSECNV(3g,L)




bx, by   Define the coordinates of the beginning point of the arc.

ex, ey   Define the coordinates of the ending point of the arc.

rot      Specifies whether the application must perform rotational
         transformation.  Possible settings are:

         0    The coordinates of the beginning and ending points passed by the
              application correspond to an arc of an orthogonal ellipse.  No
              rotational transformation is performed, thus improving
              performance.

         1    The beginning and ending points are transformed by the
              application and lie on the off-axis ellipse.

         All other values are reserved and must not be used, as they may
         produce unpredictable results.

len      Defines the number of points in the coordinate x and y arrays.  It
         must be numerically at least one greater than the value contained in
         the precision parameter and greater than or equal to 65.

x, y     Define, as coordinate arrays, the vertices that represent the
         elliptical shape when drawn or filled.

pre      Defines precision level, which specifies the maximum number of line
         segments that can be generated for a full ellipse.  The number of line
         segments actually generated depends on the size of the ellipse.

         There are four levels of precision that can be requested:

           o 64 (65 vertices)

           o 128 (129 vertices)

           o 256 (257 vertices)

           o 512 (513 vertices).

         Therefore, len => pre + 1.

         All other precision values are reserved and must not be used, as their
         results are unpredictable.  The default value for pre is 64.

The subroutine allows ample leniency toward the accuracy of the specification
of the beginning and ending points.  The arc of the specified angle always
starts and ends exactly at the specified points.  If the beginning and ending
points are identical, a full ellipse of the specified angle is generated.

When the subroutine is invoked, the length parameter must contain the maximum
number of entries in the x and y arrays.  If erroneous conditions arise, len is



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GSECNV(3g,L)                AIX Technical Reference                GSECNV(3g,L)



set to 0.  Under normal conditions, len specifies the number of vertices
returned by the subroutine in the x and y arrays.

For Pascal, the application must declare the arrays passed as being fixed
length and declare the routine as accepting arrays of that length; the k in the
routine declaration must be a constant.

RETURN VALUE

GS_SUCC  Successful.
GS_CORD  Invalid coordinate.
GS_NCOR  Invalid number of coordinates.











































Processed November 7, 1990       GSECNV(3g,L)                                 3