NV21数据的旋转

　　镜像之后，果然要旋转。于是从网上搜索了几个算法，并进行了验证、优化。分享给大家。

　　需要提醒的是，如果进行编码，注意90、270时，宽高要进行对换。

    public static byte[] NV21_rotate_to_270(byte[] nv21_data, byte[] nv21_rotated, int width, int height)
    {
        int y_size = width * height;
        int i = 0;
     
        // Rotate the Y luma
        for (int x = width - 1; x >= 0; x--)
        {
            int offset = 0;
            for (int y = 0; y < height; y++)
            {
                nv21_rotated[i] = nv21_data[offset + x];
                i++;
                offset += width;
            }
        }
     
        // Rotate the U and V color components
        i = y_size;
        for (int x = width - 1; x > 0; x = x - 2)
        {
            int offset = y_size;
            for (int y = 0; y < height / 2; y++)
            {
                nv21_rotated[i] = nv21_data[offset + (x - 1)];
                i++;
                nv21_rotated[i] = nv21_data[offset + x];
                i++;
                offset += width;
            }
        }
        return nv21_rotated;
    }
        
    public static byte[] NV21_rotate_to_180(byte[] nv21_data, byte[] nv21_rotated, int width, int height)
    {
        int y_size = width * height;
        int buffser_size = y_size * 3 / 2;
        int i = 0;
        int count = 0;
     
        for (i = y_size - 1; i >= 0; i--)
        {
            nv21_rotated[count] = nv21_data[i];
            count++;
        }

        for (i = buffser_size - 1; i >= y_size; i -= 2)
        {
            nv21_rotated[count++] = nv21_data[i - 1];
            nv21_rotated[count++] = nv21_data[i];
        }
        return nv21_rotated;
    }
     
    public static byte[] NV21_rotate_to_90(byte[] nv21_data, byte[] nv21_rotated, int width, int height)
    {
        int y_size = width * height;
        int buffser_size = y_size * 3 / 2;
        
        // Rotate the Y luma
        int i = 0;
        int startPos = (height - 1)*width;
        for (int x = 0; x < width; x++)
        {
            int offset = startPos;
            for (int y = height - 1; y >= 0; y--)
            {
                nv21_rotated[i] = nv21_data[offset + x];
                i++;
                offset -= width;
            }
        }
     
        // Rotate the U and V color components
        i = buffser_size - 1;
        for (int x = width - 1; x > 0; x = x - 2)
        {
            int offset = y_size;
            for (int y = 0; y < height / 2; y++)
            {
                nv21_rotated[i] = nv21_data[offset + x];
                i--;
                nv21_rotated[i] = nv21_data[offset + (x - 1)];
                i--;
                offset += width;
            }
        }
        return nv21_rotated;
    }