Android Open Source - Android-Sessions Bouncy Ball View

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License

The source code is released under:

MIT License

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Java Source Code

package uk.ac.icappsoc.appsocthree.accel;
/* w w w.  ja v  a  2s  . c o  m*/
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

/** A ball that expects {@link #setGravity(float, float)} and consists of a bouncing ball. */
public class BouncyBallView extends View {

  // position, velocity and acceleration of ball
  private float x, y;
  private float vx, vy;
  private float ax, ay;
  
  // 1 radian = 57.2957795 degrees
  private static final float DEGREES_PER_RADIAN = 57.2957795f;
  private static final float FRICTION = 0.98f;
  private static final float RESTITUTION = 0.9f;
  
  private float radius;
  private Paint paint;
  
  public BouncyBallView(Context context, AttributeSet attrs) {
    super(context, attrs);
    
    float density = getResources().getDisplayMetrics().density;
    radius = density * 50;
    
    paint = new Paint();
    paint.setColor(Color.WHITE);
    paint.setAntiAlias(true);
    paint.setStrokeWidth(3 * density);
  }
  
  /**
   * Updates the latest gravity values.
   */
  public void setGravity(float gravx, float gravy){
    this.ax = gravx;
    this.ay = gravy;
  }
  
  @Override
  public void onDraw(Canvas canvas){
    super.onDraw(canvas);
    
    // update ball dynamics
    vx += ax;
    vy += ay;
    
    x += vx;
    y += vy;
    
    vx *= FRICTION;
    vy *= FRICTION;
    
    // collide with view boundaries
    if(x < radius){
      x = radius;
      vx *= -RESTITUTION;
    } else if(x > getWidth() - radius){
      x = getWidth() - radius;
      vx *= -RESTITUTION;
    }
    if(y < radius){
      y = radius;
      vy *= -RESTITUTION;
    } else if(y > getHeight() - radius){
      y = getHeight() - radius;
      vy *= -RESTITUTION;
    }
    
    // draw the ball
    canvas.drawCircle(x, y, radius, paint);
    // draw the direction of our acceleration
    drawGravDirection(canvas, getWidth() / 2, getHeight() / 2);
    
    // draw us again ASAP!
    invalidate();
  }

  private void drawGravDirection(Canvas canvas, float originX, float originY){
    float gravAngleDegrees = (float) (Math.atan2(ay, ax)) * DEGREES_PER_RADIAN;
    float gravMag = (float) Math.sqrt(ax * ax + ay * ay);
    
    // save canvas for future Canvas#restore() 'cause we'll be messing with it
    canvas.save();
    
    // offset start to origin
    canvas.translate(originX, originY);
    // rotate around origin
    canvas.rotate(gravAngleDegrees);
    // draw straight line (which will end up with the angle of the previous rotation)
    canvas.drawLine(0, 0, gravMag * radius / 5, 0, paint);
    
    // offset to tip of 'arrow'
    canvas.translate(gravMag * radius / 5, 0);
    // draw arrow tips
    canvas.rotate(135);
    canvas.drawLine(0, 0, radius / 5, 0, paint);
    canvas.rotate(90);
    canvas.drawLine(0, 0, radius / 5, 0, paint);
    
    // restore canvas to normal
    canvas.restore();
  }
}

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