pt_continues_arc()

static int pt_continues_arc ( const POINT4D *  a1, const POINT4D *  a2, const POINT4D *  a3, const POINT4D *  b  )

static

Returns LW_TRUE if b is on the arc formed by a1/a2/a3, but not within that portion already described by a1/a2/a3.

Definition at line 799 of file lwstroke.c.

References distance2d_pt_pt(), EPSILON_SQLMM, lw_arc_angle(), lw_arc_center(), LW_FALSE, lw_segment_side(), LW_TRUE, and LWDEBUGF.

Referenced by pta_unstroke().

{
        POINT2D center;
        POINT2D *t1 = (POINT2D*)a1;
        POINT2D *t2 = (POINT2D*)a2;
        POINT2D *t3 = (POINT2D*)a3;
        POINT2D *tb = (POINT2D*)b;
        double radius = lw_arc_center(t1, t2, t3, &center);
        double b_distance, diff;

        /* Co-linear a1/a2/a3 */
        if ( radius < 0.0 )
                return LW_FALSE;

        b_distance = distance2d_pt_pt(tb, &center);
        diff = fabs(radius - b_distance);
        LWDEBUGF(4, "circle_radius=%g, b_distance=%g, diff=%g, percentage=%g", radius, b_distance, diff, diff/radius);

        /* Is the point b on the circle? */
        if ( diff < EPSILON_SQLMM )
        {
                int a2_side = lw_segment_side(t1, t3, t2);
                int b_side  = lw_segment_side(t1, t3, tb);
                double angle1 = lw_arc_angle(t1, t2, t3);
                double angle2 = lw_arc_angle(t2, t3, tb);

                /* Is the angle similar to the previous one ? */
                diff = fabs(angle1 - angle2);
                LWDEBUGF(4, " angle1: %g, angle2: %g, diff:%g", angle1, angle2, diff);
                if ( diff > EPSILON_SQLMM )
                {
                        return LW_FALSE;
                }

                /* Is the point b on the same side of a1/a3 as the mid-point a2 is? */
                /* If not, it's in the unbounded part of the circle, so it continues the arc, return true. */
                if ( b_side != a2_side )
                        return LW_TRUE;
        }
        return LW_FALSE;
}

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