[Dev-C++] Help with ALLEGRO question

Hi,
I'm new to the ALLEGRO  package and when trying to compile this code
segment:

    /* for generating the 8 bit additive color lookup table */
static void add_blender8 (PALETTE pal, int x, int y, RGB *rgb)
    {  int r, g, b;
       r = (int)pal[x].r + (int)pal[y].r;   
       g = (int)pal[x].g + (int)pal[y].g;   
       b = (int)pal[x].b + (int)pal[y].b;
       rgb->r = MIN(r, 63);                 
       rgb->g = MIN(g, 63);                 
       rgb->b = MIN(b, 63);
    }

int main ();
.....

  
      PALETTE pal; 
      COLOR_MAP * color_map;  
      RGB_MAP * rgb_map;
      
      color_map = (COLOR_MAP *) malloc(sizeof(COLOR_MAP));

      create_color_table (color_map, pal, add_blender8, NULL);
.....


I get the compiler error:

      converting `void (*)(RGB *, int, int, RGB *)' to
                 `void (*)(const RGB *, int, int, RGB *)' is a
      contravariance violation.


Can any ALLEGRO experts help me on eliminating this error ?



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