FlightInterp_Andorid/java/com/example/ex4/Joystick.java

package com.example.ex4;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;

public class Joystick extends SurfaceView implements SurfaceHolder.Callback, View.OnTouchListener {

    private float centerX;
    private float centerY;
    private float baseRadius;
    private float hatRadius;
    private JoystickListener joystickCallback;
    //CTOR
    public Joystick(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        getHolder().addCallback(this);
        setOnTouchListener(this);
        if (context instanceof JoystickListener)
            joystickCallback = (JoystickListener) context;
    }
    //CTOR
    public Joystick(Context context, AttributeSet attrs, int defStyleAttr)
    {
        super(context, attrs, defStyleAttr);
        getHolder().addCallback(this);
        setOnTouchListener(this);
        if (context instanceof JoystickListener)
            joystickCallback = (JoystickListener) context;
    }
    //CTOR
    public Joystick(Context context)
    {
        super(context);
        getHolder().addCallback(this);
        setOnTouchListener(this);
        if (context instanceof JoystickListener)
            joystickCallback = (JoystickListener) context;
    }
    //instantiate dimenstions for drawing the Joystick
    private void setupDimensions()
    {
        centerX = getWidth() / 2;
        centerY = getHeight() / 2;
        baseRadius = Math.min(getWidth(), getHeight()) / 4;
        hatRadius = Math.min(getWidth(), getHeight()) / 7;
    }
    //method to be called when Joystick surface is created
    @Override
    public void surfaceCreated(SurfaceHolder surfaceHolder)
    {
        setupDimensions();
        drawJoystick(centerX, centerY);
    }
    //method to be called when Joystick surface is changed
    @Override
    public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2)
    {
        setupDimensions();
        drawJoystick(centerX,centerY);
    }
    //method to be called when Joystick sutface is destroyed
    @Override
    public void surfaceDestroyed(SurfaceHolder surfaceHolder)
    {
        //nothing...
    }
    /*when Joystick is touched, method will be called and will compute values to be sent as
    * arguments to the JoystickCallBack onJoystickMoved even handler*/
    @Override
    public boolean onTouch(View view, MotionEvent event)
    {
        if (view.equals(this))
        {
            if (event.getAction() != MotionEvent.ACTION_UP)
            {
                float displacement = (float) Math.sqrt((Math.pow(event.getX() - centerX, 2)) +
                        Math.pow(event.getY() - centerY, 2));
                if (displacement < baseRadius)
                {
                    drawJoystick(event.getX(), event.getY());
                    joystickCallback.onJoystickMoved((centerX - event.getX()) / baseRadius,
                            (event.getY() - centerY) / baseRadius, getId());
                }
                else {
                    float ratio = baseRadius / displacement;
                    float constrainedX = centerX + (event.getX() - centerX) * ratio;
                    float constrainedY = centerY + (event.getY() - centerY) * ratio;
                    drawJoystick(constrainedX, constrainedY);
                    joystickCallback.onJoystickMoved((constrainedX - centerX) / baseRadius,
                            (centerY - constrainedY) / baseRadius, getId());
                }
            } else {
                drawJoystick(centerX, centerY);
                joystickCallback.onJoystickMoved(0, 0, getId());
            }
        }
        return true;
    }
    //draw the Joystick
    private void drawJoystick(float x, float y)
    {
        if (getHolder().getSurface().isValid())
        {
            Canvas drawCanvas = this.getHolder().lockCanvas();
            Paint colors = new Paint();
            drawCanvas.drawColor(Color.WHITE);
            colors.setARGB(175, 50, 50, 50);
            drawCanvas.drawCircle(centerX, centerY, baseRadius, colors);
            colors.setARGB(200, 50, 50, 200);
            drawCanvas.drawCircle(x, y, hatRadius, colors);
            getHolder().unlockCanvasAndPost(drawCanvas);
        }
    }
    //inteface defining the onJoystickMoved event handler
    public interface JoystickListener
    {
        void onJoystickMoved(float xPercent, float yPercent, int source);
    }
}