两个Bitmap合并为一个

/**
     * 合并两张bitmap为一张
     *
     * @param background
     * @param foreground
     * @return Bitmap
     */
    public static Bitmap combineBitmap(Bitmap background, Bitmap foreground) {
        if (background == null) {
            return null;
        }
        int bgWidth = background.getWidth();
        int bgHeight = background.getHeight();
        foreground =zoomImg(foreground,200,200);
        int fgWidth = foreground.getWidth();
        int fgHeight = foreground.getHeight();
        Bitmap newmap = Bitmap.createBitmap(bgWidth, bgHeight, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(newmap);
        canvas.drawBitmap(background, 0, 0, null);
        canvas.drawBitmap(foreground, (bgWidth - fgWidth) / 2, (bgHeight - fgHeight) / 2, null);
        canvas.save(Canvas.ALL_SAVE_FLAG);
        canvas.restore();
        return newmap;
    }

    /**
     * 缩放bitmap
     * @param bm
     * @param newWidth
     * @param newHeight
     * @return
     */
    public static Bitmap zoomImg(Bitmap bm, int newWidth ,int newHeight){
        // 获得图片的宽高
        int width = bm.getWidth();
        int height = bm.getHeight();
        // 计算缩放比例
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
        // 取得想要缩放的matrix参数
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);
        // 得到新的图片
        Bitmap newbm = Bitmap.createBitmap(bm, 0, 0, width, height, matrix, true);
        return newbm;
    }