SeniorUI0502_Xfermode圆角效果

高级UI汇总​​​​​​​
SeniorUI05_Paint_Xfermode模式
##一、Effect Picture

##二、Demo
RoundImageView
##三、Requirement
自定义控件实现圆角效果
##四、Theory

• 利用Xfermode的效果，先画一个圆形的图片Dst（圆角外透明，取其透明度Da）
• 设置paint的Xfermode为PorterDuff.Mode.SRC_IN（[Sa * Da, Sc * Da]）
• 画要显示的图片Src
• canvas.restoreToCount(layerId)显示

##五、CoreCode

public class RoundImageView extends View {

    private Paint mBitmapPaint;
    private Bitmap mBitmapSrc, mBitmapDst;

    public RoundImageView(Context context) {
        this(context, null);
    }

    public RoundImageView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RoundImageView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        mBitmapPaint = new Paint();

        mBitmapSrc = BitmapFactory.decodeResource(getResources(),R.drawable.xyjy6);
        mBitmapDst =BitmapFactory.decodeResource(getResources(),R.drawable.shade);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int layerId = canvas.saveLayer(0, 0, getWidth(), getHeight(), null, Canvas.ALL_SAVE_FLAG);
        canvas.drawBitmap(mBitmapDst,0,0,mBitmapPaint);
        mBitmapPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        canvas.drawBitmap(mBitmapSrc,0,0,mBitmapPaint);
        mBitmapPaint.setXfermode(null);
        canvas.restoreToCount(layerId);
    }
}

其他Xfermode也可以实现圆角效果：
RoundImageView_DSTIN
RoundImageView_SRCATOP