Rotate sprite in libgdx by following the position of finger on android

Question

I'm trying to rotate a sprite based upon where my finger is placed on the touch screen.

I have an arrow and i want the arrow to be pointing at my finger at all times as i'm drag it around over the screen.

I could easily set the sprite to any rotation using sprite.setRotation(angle)

How should i go about this?

Much appreciated if you can point me in the right direction.

Answer 1

(ax, ay) is coordinates of the center of the arrow, and (fx, fy) is the coordinates of the finger, and a is the angle, here is some pseudocode:

dx = fx - ax
dy = fy - ay
if (dx == 0) {
    a = 90
    return
}
if (dy == 0) {
    a = 0
    return
}
//tan(a) == abs(dy) / abs(dx) therefore
a = arctan(dy / dx)
if (dx > 0 && dy > 0) {
    // do nothing, a is correct
} else if (dx > 0 && dy < 0) {
    a = 360 - a
} else if (dx < 0 && dy > 0) {
    a = 180 - a
} else {
    a = 180 + a
}

I didn't implement and test it yet, I'll do it later if there will be need