android 圆角图片的实现和封装

public class RoundCornersTransformation implements Transformation {

    private float mRadius;

    private DrawCornerImage mDrawCornerImage;

    private Paint mPaint;


    public RoundCornersTransformation(float radius, DrawCornerImage drawCornerImage) {
        mRadius = radius;
        mDrawCornerImage = drawCornerImage;
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
    }

    @Override
    public Bitmap transform(Bitmap source) {//这里为主要逻辑，原理可以套用在其他地方，比如 Glide
        int width = source.getWidth();
        int height = source.getHeight();
        Bitmap newSource = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(newSource);
        mPaint.setShader(new BitmapShader(source, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP));
        source.recycle();
        //画圆角的逻辑代码，交给 DrawCornerImage 接口的具体实现类
        mDrawCornerImage.drawCornerImage(canvas, mPaint, mRadius, width, height);
        return newSource;
    }

    @Override
    public String key() {
        return RoundCornersTransformation.class.toString();
    }
}

public interface DrawCornerImage {
    void drawCornerImage(Canvas canvas, Paint paint,float radius, int right, int bottom);
}

public class DrawTopCornerImage implements DrawCornerImage {

    @Override
    public void drawCornerImage(Canvas canvas, Paint paint, float radius, int right, int bottom) {
        //绘制一个全部圆角的矩形区域长宽分别为 right 和 bottom
        canvas.drawRoundRect(new RectF(0, 0, right, bottom), radius, radius, paint);
        //绘制一个矩形长宽分别为 right 和  bottom-radius，相当于底部和上面对齐而高度差个 radius, 和上面所绘制的并集，即为图片的可见区域。并集即为上部为圆角而底部是直角的一个区域
        canvas.drawRect(new RectF(0, radius, right, bottom), paint);

    }
}

Picasso.with(this)
                .load(R.drawable.ic_girl)
                .transform(new RoundCornersTransformation(corner, new DrawTopLeftCornerImage()))// here change draw strategy：DrawAllCornerImage ,DrawBottomCornerImage etc.
                .into(iv);

    @Override
    public Bitmap transform(Bitmap source) {
        float ivWidth = 600;//600 为布局中,在我测试机中 ImageView 的像素大小
        float ivHeight = 600;//600 为布局中, 在我测试机中 ImageView 的像素大小
        int width = source.getWidth();
        int height = source.getHeight();
        //按照 ImageView 的大小创建一个 Bitmap
        Bitmap newSource = Bitmap.createBitmap(ivWidth , ivHeight , Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(newSource);
        BitmapShader bitmapShader = new BitmapShader(source, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        float scale;
       // ImageView 和原图片的宽高比，取其大值为了放大后能够完全覆盖 ImageView 的大小
        scale = Math.max(ivWidth / width, ivHeight / height);
       //利用 Matrix 矩阵进行缩放和居中操作
        mShaderMatrix.reset();
        mShaderMatrix.setScale(scale, scale);
       //将放大后的图片向上移动，达到中心位置（实际情况根据图片的各种大小，有可能也会在 x 轴方向进行移动，这里仅作示例演示）
        mShaderMatrix.postTranslate(0, -(height * scale - ivHeight) / 2.0f);
        bitmapShader.setLocalMatrix(mShaderMatrix);
        mPaint.setShader(bitmapShader);
        source.recycle();
        mDrawCornerImage.drawCornerImage(canvas, mPaint, mRadius, ivWidth, ivHeight);
        return newSource;
    }