rotate() in Tkinter

Stephen D Evans stevee at recombinant.demon.co.uk
Wed Dec 6 21:28:50 CET 2000


To rotate an oval convert the oval to a polygon and rotate that. Polygons are
easy to rotate, but this has to be done to the points before calling
create_polygon().

Referring to Tk documentation - The canvas does not support rotation.
'Practical Programming in Tcl and Tk', 3rd edition, 2000, by Brent B. Welsh,
publisher Prentice Hall PTR

This is a simple example.

(There are better methods of creating the points for an oval. Try fast
generation of ellipsoids in 'Graphics Gems V', 1995, edited by Alan W Paeth,
publisher AP Professional)

#
#
import math
import Tkinter


def poly_oval(x0,y0, x1,y1, steps=20, rotation=0):
    """return an oval as coordinates suitable for create_polygon"""

    # x0,y0,x1,y1 are as create_oval

    # rotation is in degrees anti-clockwise, convert to radians
    rotation = rotation * math.pi / 180.0

    # major and minor axes
    a = (x1 - x0) / 2.0
    b = (y1 - y0) / 2.0

    # center
    xc = x0 + a
    yc = y0 + b

    point_list = []

    # create the oval as a list of points
    for i in range(steps):

        # Calculate the angle for this step
        # 360 degrees == 2 pi radians
        theta = (math.pi * 2) * (float(i) / steps)

        x1 = a * math.cos(theta)
        y1 = b * math.sin(theta)

        # rotate x, y
        x = (x1 * math.cos(rotation)) + (y1 * math.sin(rotation))
        y = (y1 * math.cos(rotation)) - (x1 * math.sin(rotation))

        point_list.append(round(x + xc))
        point_list.append(round(y + yc))

    return point_list



import Tkinter
root = Tkinter.Tk()
canvas = Tkinter.Canvas(root, width=400, height=400)

dict = {}
dict['outline'] = 'black'
dict['fill']   = 'yellow'
dict['smooth'] = 'true'

# use a polygon to draw an oval rotated 30 degrees anti-clockwise
apply(canvas.create_polygon, tuple(poly_oval(40,40, 200,300, rotation=30)),
dict)

canvas.pack()
root.mainloop()

-- Stephen D Evans


Dethe Elza wrote:

> I'm trying to create a complex cursor in Tkinter.  I want to have an image
> which I can rotate, change the color of, and move about.  I can build it as
> a vector image, but I use ovals.  I haven't found any way to rotate images,
> vector drawings, or ovals in Tk.
>
> TIA
>
> --Dethe
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