If you are using your own image rendering and I/O functions, you can use any channel ordering. The drawing functions process each channel independently and do not depend on the channel order or even on the used color space. The whole image can be converted from BGR to RGB or to a different color space using
If a drawn figure is partially or completely outside the image, the drawing functions clip it. Also, many drawing functions can handle pixel coordinates specified with sub-pixel accuracy. This means that the coordinates can be passed as fixed-point numbers encoded as integers. The number of fractional bits is specified by the ``shift`` parameter and the real point coordinates are calculated as
:math:`\texttt{Point}(x,y)\rightarrow\texttt{Point2f}(x*2^{-shift},y*2^{-shift})` . This feature is especially effective when rendering antialiased shapes.
..note:: The functions do not support alpha-transparency when the target image is 4-channel. In this case, the ``color[3]`` is simply copied to the repainted pixels. Thus, if you want to paint semi-transparent shapes, you can paint them in a separate buffer and then blend it with the main image.
..ocv:function:: void ellipse(Mat& img, Point center, Size axes, double angle, double startAngle, double endAngle, const Scalar& color, int thickness=1, int lineType=8, int shift=0)
:param box:Alternative ellipse representation via :ocv:class:`RotatedRect` or ``CvBox2D``. This means that the function draws an ellipse inscribed in the rotated rectangle.
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
:ocv:func:`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`` . The figure below explains the meaning of the parameters.
This function is much faster than the function ``fillPoly`` . It can fill not only convex polygons but any monotonic polygon without self-intersections,
that is, a polygon whose contour intersects every horizontal line (scan line) twice at the most (though, its top-most and/or the bottom edge could be horizontal).
:param font:Pointer to the font structure initialized by the function
:param fontFace:Font name identifier. Only a subset of Hershey fonts http://sources.isc.org/utils/misc/hershey-font.txt are supported now:
***CV_FONT_HERSHEY_SIMPLEX** normal size sans-serif font
***CV_FONT_HERSHEY_PLAIN** small size sans-serif font
***CV_FONT_HERSHEY_DUPLEX** normal size sans-serif font (more complex than ``CV_FONT_HERSHEY_SIMPLEX`` )
***CV_FONT_HERSHEY_COMPLEX** normal size serif font
***CV_FONT_HERSHEY_TRIPLEX** normal size serif font (more complex than ``CV_FONT_HERSHEY_COMPLEX`` )
***CV_FONT_HERSHEY_COMPLEX_SMALL** smaller version of ``CV_FONT_HERSHEY_COMPLEX``
***CV_FONT_HERSHEY_SCRIPT_SIMPLEX** hand-writing style font
***CV_FONT_HERSHEY_SCRIPT_COMPLEX** more complex variant of ``CV_FONT_HERSHEY_SCRIPT_SIMPLEX``
The parameter can be composited from one of the values above and an optional ``CV_FONT_ITALIC`` flag, which indicates italic or oblique font.
:param hscale:Horizontal scale. If equal to ``1.0f`` , the characters have the original width depending on the font type. If equal to ``0.5f`` , the characters are of half the original width.
:param vscale:Vertical scale. If equal to ``1.0f`` , the characters have the original height depending on the font type. If equal to ``0.5f`` , the characters are of half the original height.
:param shear:Approximate tangent of the character slope relative to the vertical line. A zero value means a non-italic font, ``1.0f`` means about a 45 degree slope, etc.
The function ``line`` draws the line segment between ``pt1`` and ``pt2`` points in the image. The line is clipped by the image boundaries. For non-antialiased lines with integer coordinates, the 8-connected or 4-connected Bresenham algorithm is used. Thick lines are drawn with rounding endings.
Antialiased lines are drawn using Gaussian filtering. To specify the line color, you may use the macro ``CV_RGB(r, g, b)`` .
The class ``LineIterator`` is used to get each pixel of a raster line. It can be treated as versatile implementation of the Bresenham algorithm where you can stop at each pixel and do some extra processing, for example, grab pixel values along the line or draw a line with an effect (for example, with XOR operation).
:param thickness:Thickness of lines that make up the rectangle. Negative values, like ``CV_FILLED`` , mean that the function has to draw a filled rectangle.
The function ``rectangle`` draws a rectangle outline or a filled rectangle whose two opposite corners are ``pt1`` and ``pt2``, or ``r.tl()`` and ``r.br()-Point(1,1)``.
..ocv:cfunction:: void cvPolyLine( CvArr* img, CvPoint** pts, int* npts, int contours, int isClosed, CvScalar color, int thickness=1, int lineType=8, int shift=0 )
:param isClosed:Flag indicating whether the drawn polylines are closed or not. If they are closed, the function draws a line from the last vertex of each curve to its first vertex.
:param fontFace:Font type. One of ``FONT_HERSHEY_SIMPLEX``, ``FONT_HERSHEY_PLAIN``, ``FONT_HERSHEY_DUPLEX``, ``FONT_HERSHEY_COMPLEX``, ``FONT_HERSHEY_TRIPLEX``, ``FONT_HERSHEY_COMPLEX_SMALL``, ``FONT_HERSHEY_SCRIPT_SIMPLEX``, or ``FONT_HERSHEY_SCRIPT_COMPLEX``,
