Android自定义View实现叶子飘动旋转效果（四）

上一篇实现了叶子飘动功能，《Android自定义叶子飘动》 现在实现旋转效果

要实现这个效果，要在之前的功能上添加2个功能

1、通过matrix.postTranslate(int x, int y)在添加在Y轴上滑动

2、通过matrix.postRotate(float degrees, float px, float py)实现叶子旋转

代码实现

1、获取Y坐标

 private float getMatrixY() {
    float w = (float) ((float) 2 * Math.PI / width);
    int y = (int) (18 * Math.sin(w * getMatrixX())) + (height-mLeafHeight)/2;
    return y;
  }

math.sin(Math.PI....)的取值范围貌似是-1~1之间。通过X坐标在整个width的比例，获取到Y坐标的比例。

这里方法有很多，我这边叶子Y坐标默认在Y轴中间，然后上下+-18px实现在Y轴的滑动，18滑动浮动比较大了

public LeafView(Context context, AttributeSet attrs) {
    super(context, attrs);
    mResources = getResources();
    bgBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf_kuang, null)).getBitmap();
    leafBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf, null))).getBitmap();
   mLeafHeight = leafBitmap.getWidht();   

    bgPaint = new Paint();
    bgPaint.setColor(mResources.getColor(R.color.bg_color));
  }

  @Override
  protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    width = w;
    height = h;
    bgDestRect = new Rect(0, 0 , width, height);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    bgRect = new RectF(0, 0 , width, height);
    //添加黄色背景
    canvas.drawRect(bgRect, bgPaint);
    //添加背景图片
    canvas.drawBitmap(bgBitmap, null, bgDestRect, null);
    //添加叶子
    Matrix matrix = new Matrix();
    matrix.postTranslate(getMatriX(), getMatrixY);
    canvas.drawBitmap(leafBitmap, new Matrix(), new Paint());
    //重复调用onDraw()
    postInvalidate();
  }

  long cycleTime = 5000;  //叶子滑动一周的时间5秒
  long startTime = 0;   //叶子滑动开始时间
  private float getMatriX() {
    float betweenTime = startTime - System.currentTimeMillis();
    //周期结束再加一个cycleTime
    if(betweenTime < 0) {
      startTime = System.currentTimeMillis() + cycleTime;
      betweenTime = cycleTime;
    }
    //通过时间差计算出叶子的坐标
    float fraction = (float) betweenTime / cycleTime;
    float x = (int)(width * fraction);
    return x;
  }
  
  private float getMatrixY() {
    float w = (float) ((float) 2 * Math.PI / width);
    int y = (int) (18 * Math.sin(w * getMatrixX())) + (height-mLeafHeight)/2;
    return y;
  }

看下效果就这样，在Y轴上实现上下浮动，如果要浮动小点，可以把18改小

2、实现旋转

主要通过matrix.postRotate(float degrees, float px, float py)

degrees就是角度（0~360），px，py就是图片的中心点

  private int getRotate() {
    float scale = ((startTime - System.currentTimeMillis())%cycleTime)/ (float)cycleTime;
    int rotate = (int)(scale * 360);
    return rotate;
  }

同样，通过当前叶子在X轴的比例，来计算出旋转的角度(0~360)

完整代码：

public class LeafView extends View {
  private Resources mResources;
  private Bitmap mLeafBitmap, bgBitmap;
  private int width, height;
  private int mLeafWidth,mLeafHeight;
  private Paint bgPaint;
  private RectF bgRect;
  private Rect bgDestRect;

  public LeafView(Context context, AttributeSet attrs) {
    super(context, attrs);
    mResources = getResources();
    mLeafBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf, null)).getBitmap();
    mLeafWidth = mLeafBitmap.getWidht();
    mLeafHeight = mLeafBitmap.getHeight();
    bgBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf_kuang, null)).getBitmap();

    bgPaint = new Paint();
    bgPaint.setColor(mResources.getColor(R.color.bg_color));
  }

  @Override
  protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    width = w;
    height = h;
    bgDestRect = new Rect(0, 0 , width, height);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    bgRect = new RectF(0, 0 , width, height);
    //添加黄色白金
    canvas.drawRect(bgRect, bgPaint);
    //添加背景图片
    canvas.drawBitmap(bgBitmap, null, bgDestRect, null);

    canvas.save();
    Matrix matrix = new Matrix();
    //添加滑动
    matrix.postTranslate(getMatrixX(), getMatrixY());
    //添加旋转
    matrix.postRotate(getRotate(), getMatrixX() + mLeafWidth / 2, getMatrixY() + mLeafHeight / 2);
    canvas.drawBitmap(mLeafBitmap, matrix, new Paint());
    canvas.restore();
    postInvalidate();

  }
  long cycleTime = 5000;  //叶子滑动一周的时间5秒
  long startTime = 0;
  private float getMatrixX() {
    float betweenTime = startTime - System.currentTimeMillis();
    //周期结束再加一个cycleTime
    if(betweenTime < 0) {
      startTime = System.currentTimeMillis() + cycleTime;
      betweenTime = cycleTime;
    }
    //通过时间差计算出叶子的坐标
    float fraction = (float) betweenTime / cycleTime;
    float x = (int)(width * fraction);
    return x;
  }
  private float getMatrixY() {
    float w = (float) ((float) 2 * Math.PI / width);
    int y = (int) (18 * Math.sin(w * getMatrixX())) + (height-mLeafHeight)/2;
    return y;
  }
  private int getRotate() {
    float scale = ((startTime - System.currentTimeMillis())%cycleTime)/ (float)cycleTime;
    int rotate = (int)(scale * 360);
    return rotate;
  }
}

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