/**
 * Created by AItsuki on 2016/1/12.
 */
public class BallView extends View {

    private final Random mRandom;

    class Ball {
        int radius; // 半徑
        float cx;   // 圓心
        float cy;   // 圓心
        float vx; // X軸速度
        float vy; // Y軸速度
        Paint paint;

        // 移動(dòng)
        void move() {
            //向角度的方向移動(dòng)，偏移圓心
            cx += vx;
            cy += vy;
        }

        int left() {
            return (int) (cx - radius);
        }

        int right() {
            return (int) (cx +radius);
        }

        int bottom() {
            return (int) (cy + radius);
        }

        int top() {
            return (int) (cy - radius);
        }
    }

    private int mCount = 40;   // 小球個(gè)數(shù)
    private int maxRadius;  // 小球最大半徑
    private int minRadius; // 小球最小半徑
    private int minSpeed = 5; // 小球最小移動(dòng)速度
    private int maxSpeed = 20; // 小球最大移動(dòng)速度

    private int mWidth = 200;
    private int mHeight = 200;


    public Ball[] mBalls;   // 用來保存所有小球的數(shù)組

    public BallView(Context context, AttributeSet attrs) {
        super(context, attrs);

        // 初始化所有球(設(shè)置顏色和畫筆, 初始化移動(dòng)的角度)
        mRandom = new Random();
        RandomColor randomColor = new RandomColor(); // 隨機(jī)生成好看的顏色，github開源庫(kù)。
        mBalls = new Ball[mCount];

        for(int i=0; i< mCount; i++) {
            mBalls[i] = new Ball();
            // 設(shè)置畫筆
            Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
            paint.setColor(randomColor.randomColor());
            paint.setStyle(Paint.Style.FILL);
            paint.setAlpha(180);
            paint.setStrokeWidth(0);

            // 設(shè)置速度
            float speedX = (mRandom.nextInt(maxSpeed -minSpeed +1)+5)/10f;
            float speedY = (mRandom.nextInt(maxSpeed -minSpeed +1)+5)/10f;
            mBalls[i].paint = paint;
            mBalls[i].vx = mRandom.nextBoolean() ? speedX : -speedX;
            mBalls[i].vy = mRandom.nextBoolean() ? speedY : -speedY;
        }

        // 圓心和半徑測(cè)量的時(shí)候才設(shè)置
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        mWidth = resolveSize(mWidth, widthMeasureSpec);
        mHeight = resolveSize(mHeight, heightMeasureSpec);
        setMeasuredDimension(mWidth, mHeight);
        maxRadius = mWidth/12;
        minRadius = maxRadius/2;

        // 初始化圓的半徑和圓心
        for (int i=0; i<mBalls.length; i++) {
            mBalls[i].radius = mRandom.nextInt(maxRadius+1 - minRadius) +minRadius;
//            mBalls[i].mass = (int) (Math.PI * mBalls[i].radius * mBalls[i].radius);
            // 初始化圓心的位置， x最小為 radius， 最大為mwidth- radius
            mBalls[i].cx = mRandom.nextInt(mWidth - mBalls[i].radius) + mBalls[i].radius;
            mBalls[i].cy = mRandom.nextInt(mHeight - mBalls[i].radius) + mBalls[i].radius;
        }
    }

 

    @Override
    protected void onDraw(Canvas canvas) {
        long startTime = System.currentTimeMillis();

        // 先畫出所有圓
        for (int i = 0; i < mCount; i++) {
            Ball ball = mBalls[i];
            canvas.drawCircle(ball.cx, ball.cy, ball.radius, ball.paint);
        }

        // 球碰撞邊界
        for (int i = 0; i < mCount; i++) {
            Ball ball = mBalls[i];
            collisionDetectingAndChangeSpeed(ball); // 碰撞邊界的計(jì)算
            ball.move(); // 移動(dòng)
        }

        long stopTime = System.currentTimeMillis();
        long runTime = stopTime - startTime;
        // 16毫秒執(zhí)行一次
        postInvalidateDelayed(Math.abs(runTime -16));
    }

 

    // 判斷球是否碰撞碰撞邊界
    public void collisionDetectingAndChangeSpeed(Ball ball) {
        int left = getLeft();
        int top = getTop();
        int right = getRight();
        int bottom = getBottom();

        float speedX = ball.vx;
        float speedY = ball.vy;

        // 碰撞左右，X的速度取反。 speed的判斷是防止重復(fù)檢測(cè)碰撞，然后黏在墻上了=。=
        if(ball.left() <= left && speedX < 0) {
            ball.vx = -ball.vx;
        } else if(ball.top() <= top && speedY < 0) {
            ball.vy = -ball.vy;
        } else if(ball.right() >= right && speedX >0) {
            ball.vx = -ball.vx;
        } else if(ball.bottom() >= bottom && speedY >0) {
            ball.vy = -ball.vy;
        }
    }

}