Android Open Source - RoboDroid Joystick View

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Back to project page RoboDroid.
License

The source code is released under:
Apache License
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Java Source Code

package ch.bfh.mobilecomputing.fs2014.robodroid;
//from w w  w  . j  a  va 2s  . co m
import java.util.LinkedList;
import java.util.List;

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

public class JoystickView extends View {
  private int centerX, centerY;
  private float posX, posY;

  private int stickRadius;
  private int radius;

  private Paint linePaint;
  private Paint stickPaint;

  private List<JoystickEvent> eventListeners = new LinkedList<>();

  public JoystickView(Context context) {
    super(context);
    init();
  }

  public JoystickView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  private void init() {
    linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    linePaint.setColor(Color.LTGRAY);
    linePaint.setStyle(Paint.Style.STROKE);

    stickPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    stickPaint.setColor(Color.DKGRAY);
    stickPaint.setStyle(Paint.Style.FILL);
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // get the diameter
    int d = Math.min(MeasureSpec.getSize(widthMeasureSpec),
        MeasureSpec.getSize(heightMeasureSpec));

    setMeasuredDimension(d, d);

    // before measure, get the center of view
    centerX = (int) getWidth() / 2;
    centerY = (int) getHeight() / 2;
    if (posX == 0) {
      posX = centerX;
      posY = centerY;
    }

    radius = d / 2;
    stickRadius = (int) (radius * 0.25);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    centerX = (getWidth()) / 2;
    centerY = (getHeight()) / 2;

    canvas.drawCircle(centerX, centerY, radius * 1.0f, linePaint);
    canvas.drawCircle(centerX, centerY, radius * 0.5f, linePaint);

    canvas.drawLine(centerX, centerY - radius, centerX, centerY + radius,
        linePaint);
    canvas.drawLine(centerX - radius, centerY, centerX + radius, centerY,
        linePaint);

    // painting the move button
    canvas.drawCircle(posX, posY, stickRadius, stickPaint);
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    if (event.getAction() == MotionEvent.ACTION_UP) {
      posX = centerX;
      posY = centerY;
      fireJoystickMove(0, 0);
      invalidate();
      return true;
    }
    posX = event.getX();
    posY = event.getY();
    float x = posX - centerX;
    float y = posY - centerY;
    float abs = (float) Math.sqrt((posX - centerX) * (posX - centerX)
        + (posY - centerY) * (posY - centerY));

    if (abs > radius - stickRadius) {
      float f = (radius - stickRadius) / abs;
      x = x * f;
      y = y * f;
      posX = x + centerX;
      posY = y + centerY;
    }
    fireJoystickMove(x, y);
    invalidate();
    return true;
  }

  private void fireJoystickMove(float x, float y) {
    float max = radius - stickRadius;
    float rX = x / max;
    float rY = y / max;
    for (JoystickEvent event : eventListeners)
      event.onJoystickMove(rX, rY);
  }

  public void addEventListener(JoystickEvent eventListener) {
    eventListeners.add(eventListener);
  }

  public static interface JoystickEvent {
    /**
     * Returns relative values x, y between -1 and 1;
     * 
     * @param x
     * @param y
     */
    public void onJoystickMove(float x, float y);
  }

  private static float PI = (float) Math.PI;
  private static float PI_HALF = (float) (Math.PI / 2);

  /**
   * @param x
   * @param y
   * @return the angle between the y axis and P(x/y) in radians
   */
  public static float getAngle(float x, float y) {
    if (x != 0) {
      if (y != 0) {
        if (x > 0)
          return PI + PI_HALF - (float) Math.atan(y / x);
        else
          return PI_HALF - (float) Math.atan(y / x);
      } else {
        if (x < 0)
          return PI_HALF;
        else
          return PI + PI_HALF;
      }
    } else {
      if (y < 0) {
        return 0;
      } else {
        return PI;
      }
    }
  }

  /**
   * @param x
   * @param y
   * @return the distance between O(0/0) and P(x/y)
   */
  public static float getValue(float x, float y) {
    return (float) Math.sqrt(x * x + y * y);
  }
}
Java Source Code List
