求大神解释一下YUV数据转角的算法，为何通过几个for循环就搞定了？求解释一下每句代码的意思？

Question

  private byte[] rotateYUV420Degree270(byte[] data, int imageWidth, int imageHeight) {
        byte[] yuv = new byte[imageWidth * imageHeight * 3 / 2];
        // Rotate the Y luma
        int i = 0;
        for (int x = imageWidth - 1; x >= 0; x--) {
            for (int y = 0; y < imageHeight; y++) {
                yuv[i] = data[y * imageWidth + x];
                i++;
            }
        }// Rotate the U and V color components     i = imageWidth*imageHeight;
        for (int x = imageWidth - 1; x > 0; x = x - 2) {
            for (int y = 0; y < imageHeight / 2; y++) {
                yuv[i] = data[(imageWidth * imageHeight) + (y * imageWidth) + (x - 1)];
                i++;
                yuv[i] = data[(imageWidth * imageHeight) + (y * imageWidth) + x];
                i++;
            }
        }
        return yuv;
    }

    private static byte[] rotateYUV420Degree180(byte[] data, int imageWidth, int imageHeight) {
        byte[] yuv = new byte[imageWidth * imageHeight * 3 / 2];
        int i = 0;
        int count = 0;
        for (i = imageWidth * imageHeight - 1; i >= 0; i--) {
            yuv[count] = data[i];
            count++;
        }
        i = imageWidth * imageHeight * 3 / 2 - 1;
        for (i = imageWidth * imageHeight * 3 / 2 - 1; i >= imageWidth
                * imageHeight; i -= 2) {
            yuv[count++] = data[i - 1];
            yuv[count++] = data[i];
        }
        return yuv;
    }

    private byte[] rotateYUV420Degree90(byte[] data, int imageWidth, int imageHeight) {
        byte[] yuv = new byte[imageWidth * imageHeight * 3 / 2];
// Rotate the Y luma
        int i = 0;
        for (int x = 0; x < imageWidth; x++) {
            for (int y = imageHeight - 1; y >= 0; y--) {
                yuv[i] = data[y * imageWidth + x];
                i++;
            }
        }
// Rotate the U and V color components
        i = imageWidth * imageHeight * 3 / 2 - 1;
        for (int x = imageWidth - 1; x > 0; x = x - 2) {
            for (int y = 0; y < imageHeight / 2; y++) {
                yuv[i] = data[(imageWidth * imageHeight) + (y * imageWidth) + x];
                i--;
                yuv[i] = data[(imageWidth * imageHeight) + (y * imageWidth) + (x - 1)];
                i--;
            }
        }
        return yuv;
    }

Answer 1

因为你的转换的角度是90的整倍数，只是横边竖，左右颠倒，所以它实际上不需要三角函数，而是只要颠倒平移坐标就可以了。