/**
* 四种屏幕尺寸分类：: small, normal, large, and xlarge
* 四种密度分类: ldpi (low), mdpi (medium), hdpi (high), and xhdpi (extra high)
* 四种屏幕的DPI：ldpi是120dpi，mdpi是160dpi，hdpi是240dpi，xhdpi是320dpi
* 四种屏幕对应density：0.75,1,1.5,2
* 四种图片资源文件夹：drawable-ldpi,drawable-mdpi,drawable-hdpi,drawable-xhdpi
*/
/**
 * 圆角
 *
 * @Project App_View
 * @Package com.android.view.drawable
 * @author chenlin
 * @version 1.0
 * @Note TODO
 */
public class RoundImageDrawable extends Drawable {
 private Paint mPaint;
 private Bitmap mBitmap;
 private RectF mRectF;
 private int mRound;
 public RoundImageDrawable(Bitmap bitmap) {
  this.mBitmap = bitmap;
  mPaint = new Paint();
  mPaint.setAntiAlias(true);
  BitmapShader shader = new BitmapShader(mBitmap, TileMode.CLAMP, TileMode.CLAMP);
  mPaint.setShader(shader);
 }
 /**
  * 初始化区域
  */
 @Override
 public void setBounds(int left, int top, int right, int bottom) {
  mRectF = new RectF(left, top, right, bottom);
  super.setBounds(left, top, right, bottom);
 }
 /**
  * 核心代码： 绘制圆角
  */
 @Override
 public void draw(Canvas canvas) {
  canvas.drawRoundRect(mRectF, mRound, mRound, mPaint);
 }
 /**
  * 暴露给外面设置圆角的大小
  *
  * @param round
  */
 public void setRound(int round) {
  this.mRound = round;
 }
 /**
  * getIntrinsicWidth、getIntrinsicHeight主要是为了在View使用wrap_content的时候，
  * 提供一下尺寸，默认为-1可不是我们希望的
  */
 @Override
 public int getIntrinsicHeight() {
  return mBitmap.getHeight();
 }
 @Override
 public int getIntrinsicWidth() {
  return mBitmap.getWidth();
 }
 /**
  * 根据画笔设定drawable的透明度
  */
 @Override
 public void setAlpha(int alpha) {
  mPaint.setAlpha(alpha);
 }
 /**
  * 根据画笔设定drawable的颜色过滤器
  */
 @Override
 public void setColorFilter(ColorFilter cf) {
  mPaint.setColorFilter(cf);
 }
 @Override
 public int getOpacity() {
  return PixelFormat.TRANSLUCENT;
 }
}

public class RoundActivity extends Activity {
 private ImageView mImageView;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_round_drawable);
  setContentView(R.layout.activity_round_drawable);
  mImageView = (ImageView) findViewById(R.id.iv_round);
  Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.aa);
  RoundImageDrawable drawable = new RoundImageDrawable(bitmap);
  drawable.setRound(30);
  mImageView.setImageDrawable(drawable); }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical" >
 <ImageView
  android:id="@+id/iv_round"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:scaleType="fitXY" />
</LinearLayout>

mWidth = Math.min(bitmap.getWidth(), bitmap.getHeight());
canvas.drawCircle(mWidth / 2, mWidth / 2, mRadius, mPaint);

/**
 * 圆形
 * @Project  App_View
 * @Package  com.android.view.drawable
 * @author   chenlin
 * @version  1.0
 * @Note    TODO
 */
public class CircleImageDrawable extends Drawable {
  private Bitmap mBitmap;
  private Paint mPaint;
  private int mWidth;
  private int mRadius;
  public CircleImageDrawable(Bitmap bitmap){
    this.mBitmap = bitmap;
    mPaint.setAntiAlias(true);
    BitmapShader shader = new BitmapShader(mBitmap, TileMode.CLAMP, TileMode.CLAMP);
    mPaint.setShader(shader);
    mWidth = Math.min(bitmap.getWidth(), bitmap.getHeight());
    mRadius = mWidth / 2;
  }
  /**
   * 核心代码
   */
  @Override
  public void draw(Canvas canvas) {
    canvas.drawCircle(mWidth / 2, mWidth / 2, mRadius, mPaint);
  }
  /**
   * getIntrinsicWidth、getIntrinsicHeight主要是为了在View使用wrap_content的时候，
   * 提供一下尺寸，默认为-1可不是我们希望的
   */
  @Override
  public int getIntrinsicHeight() {
    return mWidth;
  }
  @Override
  public int getIntrinsicWidth() {
    return mWidth;
  }
  @Override
  public void setAlpha(int alpha) {
    mPaint.setAlpha(alpha);
  }
  @Override
  public void setColorFilter(ColorFilter cf) {
    mPaint.setColorFilter(cf);
  }
  @Override
  public int getOpacity() {
    return PixelFormat.TRANSLUCENT;
  }
}