Android Bitmap 圆角

第一种是生成圆角背景:

Button mView = (Button)findViewById(R.id.mView);
		
		Bitmap myCoolBitmap = ((BitmapDrawable) getResources().getDrawable(
				R.drawable.icon)).getBitmap();
		int w = myCoolBitmap.getWidth(), h = myCoolBitmap.getHeight();
		
		Bitmap rounder = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
		Canvas canvas = new Canvas(rounder);
		Paint xferPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		xferPaint.setColor(Color.RED);
		canvas.drawRoundRect(new RectF(0, 0, w, h), 20.0f, 20.0f, xferPaint);
		xferPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
		canvas.drawBitmap(myCoolBitmap, 0, 0, null);
		canvas.drawBitmap(rounder, 0, 0, xferPaint);
		
		Drawable drawable = new BitmapDrawable(rounder);  

		mView.setBackgroundDrawable(drawable);

第二种是真的圆角的位图:

public Bitmap getRoundedCornerBitmap(Bitmap bitmap) {
		// 创建一个指定宽度和高度的空位图对象
		Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),
				bitmap.getHeight(), Config.ARGB_8888);
		// 用该位图创建画布
		Canvas canvas = new Canvas(output);
		// 画笔对象
		final Paint paint = new Paint();
		// 画笔的颜色
		final int color = 0xff424242;
		// 矩形区域对象
		final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
		// 未知
		final RectF rectF = new RectF(rect);
		// 拐角的半径
		final float roundPx = 30;
		// 消除锯齿
		paint.setAntiAlias(true);
		// 画布背景色
		canvas.drawARGB(0, 0, 0, 0);
		// 设置画笔颜色
		paint.setColor(color);
		// 绘制圆角矩形
		canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
		// 未知
		paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
		// 把该图片绘制在该圆角矩形区域中
		canvas.drawBitmap(bitmap, rect, rect, paint);
		// 最终在画布上呈现的就是该圆角矩形图片，然后我们返回该Bitmap对象
		return output;
	}