plarc.c

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// plarc()
//
// Copyright (C) 2009  Hezekiah M. Carty
//
// This file is part of PLplot.
//
// PLplot is free software; you can redistribute it and/or modify
// it under the terms of the GNU Library General Public License as published
// by the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// PLplot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public License
// along with PLplot; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
//


#include "plplotP.h"

#define CIRCLE_SEGMENTS    ( PL_MAXPOLY - 1 )
#define DEG_TO_RAD( x )    ( ( x ) * M_PI / 180.0 )

void plarc_approx( PLFLT x, PLFLT y, PLFLT a, PLFLT b, PLFLT angle1, PLFLT angle2, PLFLT rotate, PLBOOL fill );

//--------------------------------------------------------------------------
// plarc_approx : Plot an approximated arc with a series of lines
//
//--------------------------------------------------------------------------
void
plarc_approx( PLFLT x, PLFLT y, PLFLT a, PLFLT b, PLFLT angle1, PLFLT angle2, PLFLT rotate, PLBOOL fill )
{
    PLINT i;
    PLFLT theta0, theta_step, theta, d_angle;
    PLINT segments;
    PLFLT xs[CIRCLE_SEGMENTS + 1], ys[CIRCLE_SEGMENTS + 1];
    PLFLT cphi, sphi, ctheta, stheta;

    // The difference between the start and end angles
    d_angle = DEG_TO_RAD( angle2 - angle1 );
    if ( fabs( d_angle ) > M_PI * 2.0 )
        d_angle = M_PI * 2.0;

    // Calculate cosine and sine of angle of major axis wrt the x axis
    cphi = cos( DEG_TO_RAD( rotate ) );
    sphi = sin( DEG_TO_RAD( rotate ) );

    // The number of line segments used to approximate the arc
    segments = (PLINT) ( fabs( d_angle ) / ( 2.0 * M_PI ) * CIRCLE_SEGMENTS );
    // Always use at least 2 arc points, otherwise fills will break.
    if ( segments < 2 )
        segments = 2;
    // The start angle in radians and number of radians in each approximating
    // segment.
    theta0 = DEG_TO_RAD( angle1 );

    theta_step = d_angle / ( segments - 1 );

    // The coordinates for the circle outline
    for ( i = 0; i < segments; i++ )
    {
        theta  = theta0 + theta_step * (PLFLT) i;
        ctheta = cos( theta );
        stheta = sin( theta );
        xs[i]  = x + a * ctheta * cphi - b * stheta * sphi;
        ys[i]  = y + a * ctheta * sphi + b * stheta * cphi;
    }

    if ( fill )
    {
        // Add the center point if we aren't drawing a circle
        if ( fabs( d_angle ) < M_PI * 2.0 )
        {
            xs[segments] = x;
            ys[segments] = y;
            segments++;
        }
        // Draw a filled arc
        plfill( segments, xs, ys );
    }
    else
    {
        // Draw the arc outline
        plline( segments, xs, ys );
    }
}

//--------------------------------------------------------------------------
// plarc : Plot an arc
//
//
//--------------------------------------------------------------------------
void
c_plarc( PLFLT x, PLFLT y, PLFLT a, PLFLT b, PLFLT angle1, PLFLT angle2, PLFLT rotate, PLBOOL fill )
{
    PLINT      xscl[2], yscl[2];
    PLINT      clpxmi, clpxma, clpymi, clpyma;
    arc_struct *arc_info;

    // TODO: For now, only unrotated plots use the driver-accelerated path.
    if ( plsc->dev_arc && plsc->diorot == 0 )
    {
        arc_info = (arc_struct *) malloc( (size_t) sizeof ( arc_struct ) );

        xscl[0] = plP_wcpcx( x - a );
        xscl[1] = plP_wcpcx( x + a );
        yscl[0] = plP_wcpcy( y - b );
        yscl[1] = plP_wcpcy( y + b );
        difilt( xscl, yscl, 2, &clpxmi, &clpxma, &clpymi, &clpyma );

        arc_info->x = 0.5 * ( xscl[1] + xscl[0] );
        arc_info->y = 0.5 * ( yscl[1] + yscl[0] );
        arc_info->a = 0.5 * ( xscl[1] - xscl[0] );
        arc_info->b = 0.5 * ( yscl[1] - yscl[0] );

        arc_info->angle1 = angle1;
        arc_info->angle2 = angle2;
        arc_info->rotate = rotate;
        arc_info->fill   = fill;

        plP_esc( PLESC_ARC, arc_info );

        free( arc_info );
    }
    else
    {
        plarc_approx( x, y, a, b, angle1, angle2, rotate, fill );
    }
}