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Im using Pythonista 2 on my IPhone, and I'm trying to create a touch joystick. Its a simple concept, I touch somewhere on my screen, the joystick and the boundary snap to that position. Then, when I move my finger, the boundary stays still but the joystick inside moves, until i get to the edge of the boundary, then it follows on the circumference of the circle in between the center of the boundary and my finger. Here is the code:

def touch_moved(self, touch):
    global r
    r = 90
    l = (touch.location-c[0],touch.location-c[1])
    a = math.degrees(math.tan(l[1]/l[0]))
    if (touch.location[0] - c[0])**2 + (touch.location[1] - c[1])**2 < r**2:
        self.joystick.position = touch.location
    else:
        self.joystick.position = ((math.cos(a)*r)+c[0],(math.sin(a)*r)+c[1])`

But the joystick spazzes out on the circumference, so any help is appreciated.

Martin Krämer
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BrrrIce
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1 Answers1

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  1. You're using a as a parameter to sin and cos, but it came from a call to math.degrees(); trig functions always operate on radians, not degrees.

  2. a is derived from the result of a call to tan, which should be a warning sign: tan uses an angle as input, not normally as an output. You probably want the inverse function here, atan. Actually, what you really want is math.atan2(), which takes the horizontal and vertical values as separate parameters. As your code is written, you will get a divide-by-zero error if the touch position is directly above or below the center point.

  3. Your calculation of l seems wrong - shouldn't you be using indexes [0] and [1] with touch.location, like you're doing two lines later?

jasonharper
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