draw_ellipse — Interactive drawing of an ellipse.
draw_ellipse returns the parameter for any orientated ellipse, which
has been created interactively by the user in the window.
The created ellipse is described by its center,
Column, its orientation,
Phi, and its two half axes,
To create an ellipse you have to determine the center of the ellipse with the
left mouse button. Keeping the button pressed determines the length (
and the orientation (
Phi) of the first half axis.
In doing so a temporary default length for the second half axis is assumed, which may be
modified afterwards on demand.
After another mouse click in the center of the created ellipse you can move it.
A mouse click close to a vertex “grips” it to modify the length of the appropriate
half axis. You may modify the orientation only, if a vertex of the first half axis is
Pressing the right mouse button terminates the procedure. On macOS
draw_ellipse can also be terminated by pressing the escape key.
After terminating the procedure the ellipse is not visible in the window any longer.
If used in a buffer window, mouse events have to be supplied by the application, while the draw operator must be run in another thread.
Row index of the center.
Column index of the center.
Orientation of the first half axis in radians.
First half axis.
Second half axis.
read_image(Image,'monkey') draw_ellipse(WindowHandle,Row,Column,Phi,Radius1,Radius2) gen_ellipse(Ellipse,Row,Column,Phi,Radius1,Radius2) reduce_domain(Image,Ellipse,GrayEllipse) sobel_amp(GrayEllipse,Sobel,'sum_abs',3) dev_display(Sobel)
draw_ellipse returns TRUE, if the window is valid and the
needed drawing mode (see
set_insert) is available.
If necessary, an exception is raised.