File content as of revision 0:be41a15e7a86:

#include "Joystick.h"

Joystick::Joystick(PinName vertPin,PinName horizPin)
{
    vert = new AnalogIn(vertPin);
    horiz = new AnalogIn(horizPin);
}

void Joystick::init()
{
    // read centred values of joystick
    _x0 = horiz->read();
    _y0 = vert->read();

    // this assumes that the joystick is centred when the init function is called
    // if perfectly centred, the pots should read 0.5, but this may
    // not be the case and x0 and y0 will be used to calibrate readings
}

Direction Joystick::get_direction()
{
    float angle = get_angle();  // 0 to 360, -1 for centred

    Direction d;
    // partition 360 into segments and check which segment the angle is in
    if (angle < 0.0f) {
        d = CENTRE;   // check for -1.0 angle
    } else if (angle < 22.5f) {  // then keep going in 45 degree increments
        d = N;
    } else if (angle < 67.5f) {
        d = NE;
    } else if (angle < 112.5f) {
        d = E;
    } else if (angle < 157.5f) {
        d = SE;
    } else if (angle < 202.5f) {
        d = S;
    } else if (angle < 247.5f) {
        d = SW;
    } else if (angle < 292.5f) {
        d = W;
    } else if (angle < 337.5f) {
        d = NW;
    } else {
        d = N;
    }

    return d;
}

// this method gets the magnitude of the joystick movement
float Joystick::get_mag()
{
    Polar p = get_polar();
    return p.mag;
}

// this method gets the angle of joystick movement (0 to 360, 0 North)
float Joystick::get_angle()
{
    Polar p = get_polar();
    return p.angle;
}

// get raw joystick coordinate in range -1 to 1
// Direction (x,y)
// North     (0,1)
// East      (1,0)
// South     (0,-1)
// West      (-1,0)
Vector2D Joystick::get_coord()
{
    // read() returns value in range 0.0 to 1.0 so is scaled and centre value
    // substracted to get values in the range -1.0 to 1.0
    float x = 2.0f*( horiz->read() - _x0 );
    float y = 2.0f*( vert->read() - _y0 );

    // Note: the values are negated so positive is up and right.
    Vector2D coord = {-x,y};
    return coord;
}

// This maps the raw x,y coord onto a circular grid.
// See:  http://mathproofs.blogspot.co.uk/2005/07/mapping-square-to-circle.html
Vector2D Joystick::get_mapped_coord()
{
    Vector2D coord = get_coord();

    // do the transformation
    float x = coord.x*sqrt(1.0f-pow(coord.y,2.0f)/2.0f);
    float y = coord.y*sqrt(1.0f-pow(coord.x,2.0f)/2.0f);

    Vector2D mapped_coord = {x,y};
    return mapped_coord;
}

// this function converts the mapped coordinates into polar form
Polar Joystick::get_polar()
{
    // get the mapped coordinate
    Vector2D coord = get_mapped_coord();

    // at this point, 0 degrees (i.e. x-axis) will be defined to the East.
    // We want 0 degrees to correspond to North and increase clockwise to 359
    // like a compass heading, so we need to swap the axis and invert y
    float x = coord.y;
    float y = coord.x;

    float mag = sqrt(x*x+y*y);  // pythagoras
    float angle = RAD2DEG*atan2(y,x);
    // angle will be in range -180 to 180, so add 360 to negative angles to
    // move to 0 to 360 range
    if (angle < 0.0f) {
        angle+=360.0f;
    }

    // the noise on the ADC causes the values of x and y to fluctuate slightly
    // around the centred values. This causes the random angle values to get
    // calculated when the joystick is centred and untouched. This is also when
    // the magnitude is very small, so we can check for a small magnitude and then
    // set the angle to -1. This will inform us when the angle is invalid and the
    // joystick is centred

    if (mag < TOL) {
        mag = 0.0f;
        angle = -1.0f;
    }

    Polar p = {mag,angle};
    return p;
}