I've tried something similar previously.

    typedef struct pixel {
        int r;
        int g;
        int b;
    } pixel_t;

    #define PIXEL(red, green, blue) \
    (pixel_t)                       \
    {                               \
      .r = (red),                   \
      .g = (green),                 \
      .b = (blue)
    }

Then I could invoke the function

    void display_pixel(pixel_t pixel);

by calling,

    display_pixel(PIXEL(255, 255, 255));

And you could even,

    return PIXEL(255, 255, 255);

Like magic. In other words, how do you pretend that you have syntax-level OOP in C... On retrospect, the macro could reduce readability, writing the argument explicitly may be better.

    display_pixel((pixel_t) {.r = 255, .g = 255, .b = 255});