Suduko

Introduction to Software Engineering (CSSE 1001)

Canvas

A tkinter Canvas is a window in which we can draw.

The following can be drawn in canvases:

• ▶ arc bitmap
  
• ▶ images
  
• ▶ lines
  
• ▶ polygons
  
• ▶ rectangles
  
• ▶ text
  
• ▶ ovals
  
• ▶ window

---

tk.Canvas

root = tk.Tk()
canvas = tk.Canvas(
    root,
    width=100,
    height=100,
    bg="pink"
   )
canvas.pack()

root.mainloop()

We assume the above has been executed from now on and will insert new code before root.mainloop().

tk.Canvas.create_text

Note we use the graphics coordinate system where the top-left corner is (0, 0) and increasing y moves south.

canvas.create_text(
    50, 100,
    text="*",
   )

canvas.create_text(
    50, 100,
    text="(50,100)",
    anchor=tk.NW
   )

tk.Canvas.create_line

canvas.create_line(
    50, 50,
    100, 100,
    fill="blue",
    width=10
)

tk.Canvas.create_rectangle

canvas.create_rectangle(
    50, 50,        # north-west corner
    100, 100,      # south-east corner
    width=1        # border width
   )

canvas.create_rectangle(
    125, 150, 175, 175,
    fill="light blue",   # fill colour
    width=10
   )

canvas.create_rectangle(
    150, 10, 190, 80,
    fill="light green",
    width=0
   )

tk.Canvas.create_window

tkinter widgets can be placed in canvases using window.

window = canvas.create_window(
    50, 50,
    width=100,
    height=50,
    window=tk.Button(text="Press Me"),   # any widget can go here
    anchor=tk.NW
   )

bind in tk.Canvas

We can bind inside canvases.

def handler(event):
    print(f"{event.x} {event.y}")

canvas.bind("<Button>", handler)

Clicking inside the canvas produces in the REPL:

178 155
81 89
151 83

Inheritance

Do not forget that tkinter objects are objects which we can use for inheritance.

class View(tk.Canvas):
    def __init__(self, master: tk.Tk, side: int, **kwargs) -> None:
        super().__init__(master,
                        width=side,
                        height=side,
                        bg="pink",
                        **kwargs)      # keyword arguments
        self.create_text(50, 50, text="*", fill="black")

root = tk.Tk()
view = View(root, 200)
view.pack()
root.mainloop()

Abstract Grid

For example, we can have an AbstractGrid class which inherits from a Canvas that extends it to include methods that interface with the canvas as if it were divided into a grid of smaller and equally sized rectangles.

class AbstractGrid(tk.Canvas):
    """A type of tkinter Canvas that provides support for
       using the canvas as a grid (i.e. a collection of
       rows and columns)."""

Sudoku Game — A tkinter Canvas

A full Sudoku game can be implemented on top of such a grid canvas.