примеры с лекций:

//typedef struct _sColorParts
//{
//    char b;
//    char g;
//    char r;
//    char A;
//}sColorParts;

typedef union _sColorParts
{
    struct    {
        char b;
        char g;
        char r;
    };
    //unsigned int Value;
}sColorParts;
#pragma pack(pop)

           //p_pixels[y * w + x] = sCONS_COLOR(x, y, x ^ y);

            //*(char*)(((unsigned int)p_pixels + y * w * sizeof(sColor) + x * sizeof(sColor) + 0)) = x ^ y;
            //*(char*)(((unsigned int)p_pixels + y * w * sizeof(sColor) + x * sizeof(sColor) + 1)) = y;
            //*(char*)(((unsigned int)p_pixels + y * w * sizeof(sColor) + x * sizeof(sColor) + 2)) = x;
            //*(char*)(((unsigned int)p_pixels + y * w * sizeof(sColor) + x * sizeof(sColor) + 3)) = 0xFF;

            //*(char*)((p_pixels + y * w + x + 0)) = x ^ y;
            //*(char*)((p_pixels + y * w + x + 1)) = y;
            //*(char*)((p_pixels + y * w + x + 2)) = x;
            //*(char*)((p_pixels + y * w + x + 3)) = 0xFF;

            //*((char*)(p_pixels + y * w + x) + 0) = x ^ y;
            //*((char*)(p_pixels + y * w + x) + 1) = y;
            //*((char*)(p_pixels + y * w + x) + 2) = x;
            //*((char*)(p_pixels + y * w + x) + 3) = 0xFF;

            //*((char*)&p_pixels[y * w + x] + 0) = x ^ y;
            //*((char*)&p_pixels[y * w + x] + 1) = y;
            //*((char*)&p_pixels[y * w + x] + 2) = x;
            //*((char*)&p_pixels[y * w + x] + 3) = 0xFF;

            int sz1 = sizeof(sColorParts);
            int sz2 = sizeof(sColor);
     
            sColorParts* p_pixel_parts = p_pixels;

            // 3145728
            // 3145725
            p_pixel_parts[y * w + x].b = x ^ y;
            p_pixel_parts[y * w + x].g = y;
            p_pixel_parts[y * w + x].r = x;

            //p_pixel_parts[y * w + x].A = 0xFF;
            //p_pixel_parts[y * w + x].Value = sCONS_COLOR(x, y, x ^ y);