BitmapShader描述:
Shader used to draw a bitmap as a texture. The bitmap can be repeated or mirrored by setting the tiling mode.
用来将bitmap 绘制为纹理的着色器。通过设置平铺模式，位图可以重复或镜像
BitmapShader是Shader的子类
BitmapShader
ComposeShader
LinearGradient
RadialGradient
SweepGradient

其他之类逐一学习使用..

test111.png

这是原图 我们要的效果是这样

Screenshot_20170629113943.png

创建一个CircleImageView继承ImageView

主要重写
onDraw
onMeasure
这两个方法

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //取宽度或者高度的最小值
        int size = Math.min(getMeasuredWidth(), getMeasuredHeight());
        mRadius = size / 2;
        setMeasuredDimension(size, size);
    } 

private float mScale; private int mRadius; //圆形图片的半径 BitmapShader mBitmapShader; Paint mBitmapPaint; @Override protected void onDraw(Canvas canvas) { //创建一个画笔 mBitmapPaint = new Paint(); //把Drawable转化为Bitmap Bitmap bitmap = getBitmapFromDrawable(getDrawable()); //设置一个BitmapShader //Shader.TileMode.CLAMP 当所画图形的尺寸大于Bitmap的尺寸的时候，会用Bitmap四边的颜色填充剩余空间 //REPEAT 重复平铺整个绘制的区域
//MIRROR 镜像平铺整个绘制的区 mBitmapShader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP); //计算缩放比例 mScale = ((mRadius * 2.0f) / Math.min(bitmap.getHeight(), bitmap.getWidth())); //可以保证显示的时候图片内容照应Shader大小,否者图片显示偏移 Matrix matrix = new Matrix(); matrix.setScale(mScale, mScale); mBitmapShader.setLocalMatrix(matrix); //添加Shader mBitmapPaint.setShader(mBitmapShader); //画圆 canvas.drawCircle(mRadius, mRadius, mRadius, mBitmapPaint);

} 

 private Bitmap getBitmapFromDrawable(Drawable drawable) {
        if (drawable == null) {
            return null;
        }
        if (drawable instanceof BitmapDrawable) {
            return ((BitmapDrawable) drawable).getBitmap();
        }
        Bitmap bitmap;
        bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(),
                drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
        drawable.draw(canvas);
        return bitmap;

    } 
```