opencv ellipse

opencv ellipse

/** @brief Draws a simple or thick elliptic arc or fills an ellipse sector.

The function cv::ellipse with more parameters draws an ellipse outline, a filled ellipse, an elliptic
arc, or a filled ellipse sector. The drawing code uses general parametric form.
A piecewise-linear curve is used to approximate the elliptic arc
boundary. If you need more control of the ellipse rendering, you can retrieve the curve using
cv::ellipse2Poly and then render it with polylines or fill it with cv::fillPoly. If you use the first
variant of the function and want to draw the whole ellipse, not an arc, pass `startAngle=0` and
`endAngle=360`. If `startAngle` is greater than `endAngle`, they are swapped. The figure below explains
the meaning of the parameters to draw the blue arc.

![Parameters of Elliptic Arc](pics/ellipse.svg)

@param img Image.
@param center Center of the ellipse.
@param axes Half of the size of the ellipse main axes.
@param angle Ellipse rotation angle in degrees.
@param startAngle Starting angle of the elliptic arc in degrees.
@param endAngle Ending angle of the elliptic arc in degrees.
@param color Ellipse color.
@param thickness Thickness of the ellipse arc outline, if positive. Otherwise, this indicates that
a filled ellipse sector is to be drawn.
@param lineType Type of the ellipse boundary. See the line description.
@param shift Number of fractional bits in the coordinates of the center and values of axes.
 */
CV_EXPORTS_W void ellipse(InputOutputArray img, Point center, Size axes,
                        double angle, double startAngle, double endAngle,
                        const Scalar& color, int thickness = 1,
                        int lineType = LINE_8, int shift = 0);

void ellipse( InputOutputArray _img, Point center, Size axes,
              double angle, double start_angle, double end_angle,
              const Scalar& color, int thickness, int line_type, int shift )
{
    CV_INSTRUMENT_REGION();

    Mat img = _img.getMat();

    if( line_type == CV_AA && img.depth() != CV_8U )
        line_type = 8;

    CV_Assert( axes.width >= 0 && axes.height >= 0 &&
        thickness <= MAX_THICKNESS && 0 <= shift && shift <= XY_SHIFT );

    double buf[4];
    scalarToRawData(color, buf, img.type(), 0);

    int _angle = cvRound(angle);
    int _start_angle = cvRound(start_angle);
    int _end_angle = cvRound(end_angle);
    Point2l _center(center);
    Size2l _axes(axes);
    _center.x <<= XY_SHIFT - shift;
    _center.y <<= XY_SHIFT - shift;
    _axes.width <<= XY_SHIFT - shift;
    _axes.height <<= XY_SHIFT - shift;

    EllipseEx( img, _center, _axes, _angle, _start_angle,
               _end_angle, buf, thickness, line_type );
}

void ellipse(InputOutputArray _img, const RotatedRect& box, const Scalar& color,
             int thickness, int lineType)
{
    CV_INSTRUMENT_REGION();

    Mat img = _img.getMat();

    if( lineType == CV_AA && img.depth() != CV_8U )
        lineType = 8;

    CV_Assert( box.size.width >= 0 && box.size.height >= 0 &&
               thickness <= MAX_THICKNESS );

    double buf[4];
    scalarToRawData(color, buf, img.type(), 0);

    int _angle = cvRound(box.angle);
    Point2l center(cvRound(box.center.x),
                 cvRound(box.center.y));
    center.x = (center.x << XY_SHIFT) + cvRound((box.center.x - center.x)*XY_ONE);
    center.y = (center.y << XY_SHIFT) + cvRound((box.center.y - center.y)*XY_ONE);
    Size2l axes(cvRound(box.size.width),
              cvRound(box.size.height));
    axes.width  = (axes.width  << (XY_SHIFT - 1)) + cvRound((box.size.width - axes.width)*(XY_ONE>>1));
    axes.height = (axes.height << (XY_SHIFT - 1)) + cvRound((box.size.height - axes.height)*(XY_ONE>>1));
    EllipseEx( img, center, axes, _angle, 0, 360, buf, thickness, lineType );
}

static void
EllipseEx( Mat& img, Point2l center, Size2l axes,
           int angle, int arc_start, int arc_end,
           const void* color, int thickness, int line_type )
{
    axes.width = std::abs(axes.width), axes.height = std::abs(axes.height);
    int delta = (int)((std::max(axes.width,axes.height)+(XY_ONE>>1))>>XY_SHIFT);
    delta = delta < 3 ? 90 : delta < 10 ? 30 : delta < 15 ? 18 : 5;

    std::vector<Point2d> _v;
    ellipse2Poly( Point2d((double)center.x, (double)center.y), Size2d((double)axes.width, (double)axes.height), angle, arc_start, arc_end, delta, _v );

    std::vector<Point2l> v;
    Point2l prevPt(0xFFFFFFFFFFFFFFFF, 0xFFFFFFFFFFFFFFFF);
    v.resize(0);
    for (unsigned int i = 0; i < _v.size(); ++i)
    {
        Point2l pt;
        pt.x = (int64)cvRound(_v[i].x / XY_ONE) << XY_SHIFT;
        pt.y = (int64)cvRound(_v[i].y / XY_ONE) << XY_SHIFT;
        pt.x += cvRound(_v[i].x - pt.x);
        pt.y += cvRound(_v[i].y - pt.y);
        if (pt != prevPt) {
            v.push_back(pt);
            prevPt = pt;
        }
    }

    // If there are no points, it's a zero-size polygon
    if (v.size() == 1) {
        v.assign(2, center);
    }

    if( thickness >= 0 )
        PolyLine( img, &v[0], (int)v.size(), false, color, thickness, line_type, XY_SHIFT );
    else if( arc_end - arc_start >= 360 )
        FillConvexPoly( img, &v[0], (int)v.size(), color, line_type, XY_SHIFT );
    else
    {
        v.push_back(center);
        std::vector<PolyEdge> edges;
        CollectPolyEdges( img,  &v[0], (int)v.size(), edges, color, line_type, XY_SHIFT );
        FillEdgeCollection( img, edges, color );
    }
}

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