画圆形背景头像

public class CircleDisplayer extends RoundedBitmapDisplayer {
    // 构造函数  public CircleDisplayer() {
        super(0);
    }

    // 显示位图  @Override
    public void display(Bitmap bitmap, ImageAware imageAware,
            LoadedFrom loadedFrom) {
        imageAware.setImageDrawable(new CircleDrawable(bitmap, margin));
    }

    public static class CircleDrawable extends Drawable {
        private final int margin;
        private final RectF mRect = new RectF();
        private final BitmapShader bitmapShader;
        private final Paint paint;
        private RectF mBitmapRect;

        public CircleDrawable(Bitmap bitmap, int margin) {
            this.margin = 0;
            // 创建着色器  bitmapShader = new BitmapShader(bitmap, Shader.TileMode.CLAMP,
                    Shader.TileMode.CLAMP);
            mBitmapRect = new RectF(margin, margin, bitmap.getWidth() - margin,
                    bitmap.getHeight() - margin);
            // 设置画笔  paint = new Paint();
            paint.setAntiAlias(true);
            paint.setShader(bitmapShader);
        }

        // 画圆，覆盖原来的位图  @Override
        protected void onBoundsChange(Rect bounds) {
            super.onBoundsChange(bounds);
            mRect.set(margin, margin, bounds.width() - margin, bounds.height()
                    - margin);

            // 调整位图，设置该矩阵，转换映射源矩形和目的矩形  Matrix shaderMatrix = new Matrix();
            shaderMatrix.setRectToRect(mBitmapRect, mRect,
                    Matrix.ScaleToFit.FILL);
            // 设置着色器矩阵  bitmapShader.setLocalMatrix(shaderMatrix);
        }

        // 画出其边界（通过设置的setBounds）  @Override
        public void draw(Canvas canvas) {
            canvas.drawRoundRect(mRect, mRect.width() / 2, mRect.height() / 2,
                    paint);
        }

        /**  * 返回此绘制对象的不透明度/透明度 ，返回的值是抽象的格式常数的PixelFormat之一：未知，半透明，透明或不透明  * */  @Override
        public int getOpacity() {
            // 半透明  return PixelFormat.TRANSLUCENT;
        }

        // 设置透明度  @Override
        public void setAlpha(int alpha) {
            paint.setAlpha(alpha);
        }

        // 彩色滤光片（通过设置setColorFilter）  @Override
        public void setColorFilter(ColorFilter cf) {
            paint.setColorFilter(cf);
        }
    }
}