#! /usr/bin/env python

#------------------------------------------------------------------------------
# Equazione della retta - By C.Fin 2013 - Python2&3
#------------------------------------------------------------------------------

try: import Tkinter as tk
except ImportError: import tkinter as tk

#------------------------------------------------------------------------------

MINX, MINY = -15.0, -15.0   # coord. virtuali angolo basso sinistra
MAXX, MAXY = 15.0, 15.0     # coord. virtuali angolo alto destra  
WID,  HEI  = 500, 500       # dimensioni in pixel area grafica
KX1 = (WID-1) / (MAXX-MINX) # coefficienti per traslazione
KX2 = -MINX * KX1 
KY1 = (1.0-HEI) / (MAXY-MINY)
KY2 = -MINY*KY1 + HEI-1
CFONDO, CASSI, CRETTA, CGRIGL = "#252500", "#ca5500", "green", "#2a2a25"

#------------------------------------------------------------------------------
  
def trasla(x, y): return round(x*KX1 + KX2), round(y*KY1 + KY2)

#------------------------------------------------------------------------------

def disegna_quadro():
    for n in range(-14, 15): # disegna griglia
        if n != 0  and  n % 2 == 0:
            x1, y1 = trasla(n, MINY)
            x2, y2 = trasla(n, MAXY)
            tela.create_line(x1, y1, x2, y2, fill=CGRIGL)
            x1, y1 = trasla(MINX, n)
            x2, y2 = trasla(MAXX, n)
            tela.create_line(x1, y1, x2, y2, fill=CGRIGL)

    for n in range(-14, 15): # disegna scale
        x1, y1 = trasla(n, -0.3)
        x2, y2 = trasla(n, 0.2)
        tela.create_line(x1, y1, x2, y2, fill=CASSI)  # Scala X
        if n != 0  and  n % 2 == 0:
            tela.create_text(x1, y1+2, fill=CASSI, anchor="n", text=str(n))

        x1, y1 = trasla(-0.2, n)
        x2, y2 = trasla(0.3, n)
        tela.create_line(x1, y1, x2, y2, fill=CASSI)  # Scala Y
        if n != 0  and  n % 2 == 0:
            tela.create_text(x1-2, y1, fill=CASSI, anchor="e", text=str(n))

    x1, y1 = trasla(MINX, 0)
    x2, y2 = trasla(MAXX, 0)
    tela.create_line(x1, y1, x2, y2, fill=CASSI, arrow="last")  # Asse X
    x1, y1 = trasla(0, MINY)
    x2, y2 = trasla(0, MAXY)
    tela.create_line(x1, y1, x2, y2, fill=CASSI, arrow="last")  # Asse Y

#------------------------------------------------------------------------------

def aggiorna(_):
    a, b = slider_a.get(), slider_b.get()
    x1, y1 = trasla(MINX, a*MINX + b)
    x2, y2 = trasla(MAXX, a*MAXX + b)
    tela.coords(retta, x1, y1, x2, y2)
    s = "Y   =   %-2.2f * X   %s   %2.1f" % (a, "+" if b>=0 else "-", abs(b))
    tela.itemconfigure(testo, text=s)

#------------------------------------------------------------------------------

finestra = tk.Tk()
finestra.resizable(False, False)
finestra.title("La retta via")
tela = tk.Canvas(finestra, highlightthickness=0)
tela.configure(bg=CFONDO, width=WID, height=HEI)
tela.pack(side="left")
cornice_a = tk.Frame(finestra)
cornice_a.pack(side="left", fill="y")
tk.Label(cornice_a, text="a").pack(side="top")    
slider_a = tk.Scale(cornice_a, from_=20.0, to=-20.0, 
                    resolution=0.01, showvalue=0, command=aggiorna)
slider_a.pack(side="top", expand=1, fill="y")
cornice_b = tk.Frame(finestra)
cornice_b.pack(side="left", fill="y")
tk.Label(cornice_b, text="b").pack(side="top")    
slider_b = tk.Scale(cornice_b, from_=20.0, to=-20.0, 
                    resolution=0.1 , showvalue=0, command=aggiorna)
slider_b.pack(side="top", expand=1, fill="y")
disegna_quadro()
retta = tela.create_line(0, 0, 0, 0, fill=CRETTA)
testo = tela.create_text(30, 30, fill=CRETTA, anchor="nw", text="")
slider_a.set(-4.0)
slider_b.set(13.0)
finestra.mainloop()