# Tk_drag_and_zoom.py

# Tk_drag_and_zoom.py

# ZZZ almost works perfectly?

from tkinter import *
from math import *

ww = 600
hh = 600

fGrid = 300

fStartPanX = -ww / 2
fStartPanY = -hh / 2
x, y = -fStartPanX - fGrid / 2, -fStartPanY - fGrid / 2

prev_x, prev_y = x, y

dx, dy = x, y

fOffsetX = fOffsetY = 0

root = Tk()
root.title("Tk_drag_and_zoom.py")

canvas = Canvas(width=ww, height=hh, background="violet")
canvas.grid(row=0, column=0, sticky="nsew")

fWorldLeft = fWorldTop = fWorldRight = fWorldBottom = 0.0

Scale = 1.0
zoom = 0 # I shouldn't need this

def WorldToScreen(DX, DY):
    global  zoom # I shouldn't need this
    XX = int(dx + DX)
    YY = int(dy + DY)
    if zoom: # I shouldn't need this
        XX, YY = scale_to_cursor(XX, YY)
        zoom = 1
    return XX, YY

def btn_1(event):
    global fOffsetX, fOffsetY
    fOffsetX = event.x - dx
    fOffsetY = event.y - dy

def motion(event):
    global x, y, prev_x, prev_y
    prev_x, prev_y = x, y
    x = event.x
    y = event.y

def drag(event):
    global x, y, dx, dy
    x = event.x
    y = event.y
    dx, dy = x - fOffsetX, y - fOffsetY
    draw()

def draw():
    canvas.delete('all')

    # Draw Main Axes a 10x10 Unit Grid
    nLinesDrawnH = 0
    nLinesDrawnV = 0
    bl = br = 0
    if dx+fGrid > 0 and dx < ww and dy+fGrid > 0 and dy < hh:
        for xy in range(0, int(fGrid)+1, int(fGrid/9)):
            if dx+xy > 0 and xy < ww:
                # Draw 10 horizontal lines
                sx, sy = WorldToScreen(xy, 0)
                ex, ey = WorldToScreen(xy, fGrid-3)
                br = ey

                canvas.create_line(sx, sy, ex, ey, fill="black")
                nLinesDrawnH += 1

            if dy+xy > 0 and xy < hh:
                # Draw 10 vertical lines
                sx, sy = WorldToScreen(0, xy)
                ex, ey = WorldToScreen(fGrid-3, xy)
                bl = ex

                canvas.create_line(sx, sy, ex, ey, fill="black")
                nLinesDrawnV += 1
        sx, sy = WorldToScreen(0, 0)
        ex, ey = WorldToScreen(fGrid, fGrid)
        if bl * br:
            obj = canvas.create_rectangle(sx, sy, bl, br, width=0, fill="white")
            canvas.lower(obj) # vs canvas.lift(obj)
            print(nLinesDrawnH, nLinesDrawnV)
    else:
        print('offscreen')

    canvas.update()

def ZoomIn(event):
    global  dx, dy, Scale, zoom
    x = event.x
    y = event.y
    Scale *= 1.01
    zoom = 1
    draw()

def ZoomOut(event):
    global  dx, dy, Scale, zoom
    x = event.x
    y = event.y
    Scale *= 0.99
    zoom = 1
    draw()

def scale_to_cursor(XX, YY): # ZZZ almost how I want it to function
    sx = (XX - prev_x) * Scale + x
    sy = (YY - prev_y) * Scale + y
    return sx, sy

root.bind("<ButtonPress-1>", btn_1)
root.bind("<B1-Motion>", drag)
root.bind("<Motion>", motion)

root.bind("<q>", ZoomIn)
root.bind("<a>", ZoomOut)

draw()
root.mainloop()