arc.c

来自「开放源码的编译器open watcom 1.6.0版的源代码」· C语言 代码 · 共 133 行

/****************************************************************************
*
*                            Open Watcom Project
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*    Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
*
*  ========================================================================
*
*    This file contains Original Code and/or Modifications of Original
*    Code as defined in and that are subject to the Sybase Open Watcom
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*    except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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* Description:  WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
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****************************************************************************/


#include "gdefn.h"


short _WCI86FAR _CGRAPH _arc( short x1, short y1, short x2, short y2,
/*====================*/ short x3, short y3, short x4, short y4 )

/* This function draws an elliptical arc.  The virtual ellipse is defined by
   the rectangle whose opposite corners are ( x1, y1 ) and ( x2, y2 ).  The
   intersections of the vectors from the center of the ellipse to the points
   ( x3, y3 ) and ( x4, y4 ) define the start and end points respectively
   where the arc is drawn in a counter clockwise direction. */

{
    short           success;

    if( _GrProlog() ) {
        success = _L2arc( _VtoPhysX( x1 ), _VtoPhysY( y1 ),
                          _VtoPhysX( x2 ), _VtoPhysY( y2 ),
                          _VtoPhysX( x3 ), _VtoPhysY( y3 ),
                          _VtoPhysX( x4 ), _VtoPhysY( y4 ) );
        if( success ) {
            _moveto( _GetLogX( _ArcInfo.end.xcoord ),
                     _GetLogY( _ArcInfo.end.ycoord ) );
        }
        _GrEpilog();
    } else {
        success = 0;
    }
    return( success );
}

Entry( _ARC, _arc ) // alternate entry-point


#define sgn( x )    ( x == 0 ? 0 : ( x < 0 ? -1 : 1 ) )


short _WCI86FAR _CGRAPH _getarcinfo( struct xycoord _WCI86FAR *start,
/*===========================*/ struct xycoord _WCI86FAR *end,
                                struct xycoord _WCI86FAR *fillpoint )

/* This function returns the starting and ending points of the last arc
   or pie drawn. The points are in viewport coordinates. The fillpoint
   is an inside point that can be used by floodfill to fill a pie slice.
   This is not used in WATCOM C Graphics which uses a specialized fill
   routine for pie slices.  */

{
    short               success;
    short               x1, y1;
    short               x2, y2;
    short               x3, y3;
    long                xprod;

    success = ( _ErrorStatus == _GROK );
    if( success ) {
        start->xcoord = _GetLogX( _ArcInfo.start.xcoord );
        start->ycoord = _GetLogY( _ArcInfo.start.ycoord );
        end->xcoord = _GetLogX( _ArcInfo.end.xcoord );
        end->ycoord = _GetLogY( _ArcInfo.end.ycoord );

        x1 = _ArcInfo.start.xcoord - _ArcInfo.centre.xcoord;
        y1 = _ArcInfo.start.ycoord - _ArcInfo.centre.ycoord;
        x2 = _ArcInfo.end.xcoord - _ArcInfo.centre.xcoord;
        y2 = _ArcInfo.end.ycoord - _ArcInfo.centre.ycoord;
        x3 = 3 * ( x1 + x2 ) / 8;
        y3 = 3 * ( y1 + y2 ) / 8;
        xprod = (long) x1 * y2 - (long) x2 * y1;
        if( xprod == 0 ) {
            if( x1 != x2 || y1 != y2 ) {    // 180 degrees apart
                x3 = sgn( y1 );     // offset from centre
                y3 = -sgn( x1 );
            }
        } else if( xprod > 0 ) {    // more than 180
            x3 = -x3;
            y3 = -y3;
        }
        fillpoint->xcoord = _GetLogX( x3 + _ArcInfo.centre.xcoord );
        fillpoint->ycoord = _GetLogY( y3 + _ArcInfo.centre.ycoord );
    }
    return( success );
}

Entry( _GETARCINFO, _getarcinfo ) // alternate entry-point


short _WCI86FAR _L2arc( short x1, short y1, short x2, short y2,
/*==============*/ short x3, short y3, short x4, short y4 )

/* This function draws an elliptical arc.  The virtual ellipse is defined by
   the rectangle whose opposite corners are ( x1, y1 ) and ( x2, y2 ). The
   intersections of the vectors from the center of the ellipse to the points
   ( x3, y3 ) and ( x4, y4 ) define the start and end points respectively
   where the arc is drawn in a counter clockwise direction. All values
   are in physical coordinates. */

{
    _L1Arc( _GBORDER, x1, y1, x2, y2, x3, y3, x4, y4 );
    return( _ErrorStatus == _GROK );
}