How to add an image in a Xforms interface in language C

I have to do an a GUI for a project and for better ergonomics i want to add images or pictures to it. For the project i have to do it in C or C++ and I'm using Xforms to create the GUI.

There is my code for the moment:

#include <stdio.h>
#include <forms.h>

#define WIDTH 800
#define LENGTH 480


FL_FORM *menu;
FL_IMAGE *skiold;
FL_OBJECT *lower_bar;
FL_OBJECT *deco;

/* ------------- */
/* main fonction */
/* ------------- */
int main(int argc, char *argv[])
{
    fl_initialize(&argc, argv, 0, 0, 0);

    menu = fl_bgn_form(FL_FLAT_BOX, WIDTH, LENGTH);
    fl_set_form_background_color(menu, FL_WHITE);

    lower_bar = fl_add_box(FL_FLAT_BOX, 0, 400, 800, 80, "");
    fl_set_object_color(lower_bar, FL_DARKER_COL1, FL_DARKER_COL1);
    deco = fl_add_text(FL_NORMAL_TEXT, 250, 420, 300, 50, "PRINCIPAL MENU");
    fl_set_object_lsize(deco, 30);
    fl_set_object_color(deco, FL_DARKER_COL1, FL_DARKER_COL1);

    /*skiold = flimage_load("logo_skiold.png")*/

    fl_end_form();
    fl_show_form(menu, FL_PLACE_MOUSE, FL_FULLBORDER, "Emulateur");
    fl_do_forms();
    fl_hide_form(menu);
    fl_finish();

    return 0;
}

From what I saw in the documentation, I just had to create a variable of type FL_IMAGE and load it after. But when I compile it, it returns that it doesn't recognize the type FL_IMAGE.

So, I don't know if this is a problem of libraries, if there are others methods or if this is just impossible.

Solution

The INSTALL doc file states that for building libflimage and its headers you must configure and make and make install as root. Then you have also a libflimage.so and an flimage.h to include.

Note: I've noy yet tested all this with your source. I've only done the build/install and got also libflimage.so and an flimage.h available

ADDENDUM Now I testes ad all is Ok, the image is displayed but a canvas is needed:

// gcc prova.c -lforms -lflimage -o prova
#include <stdio.h>
#include <forms.h>
#include <flimage.h>

#define WIDTH 800
#define LENGTH 480
    
FL_FORM *menu;
FL_IMAGE *skiold;
FL_OBJECT *lower_bar;
FL_OBJECT *deco;
FL_OBJECT *canv;

/* ------------- */
/* main fonction */
/* ------------- */
int main(int argc, char *argv[])
{
    fl_initialize(&argc, argv, 0, 0, 0);

    menu = fl_bgn_form(FL_FLAT_BOX, WIDTH, LENGTH);
    fl_set_form_background_color(menu, FL_WHITE);
    canv = fl_add_canvas(FL_NORMAL_CANVAS, 0, 0, 100, 100,"");

    lower_bar = fl_add_box(FL_FLAT_BOX, 0, 400, 800, 80, "");
    fl_set_object_color(lower_bar, FL_DARKER_COL1, FL_DARKER_COL1);
    deco = fl_add_text(FL_NORMAL_TEXT, 250, 420, 300, 50, "PRINCIPAL MENU");
    fl_set_object_lsize(deco, 30);
    fl_set_object_color(deco, FL_DARKER_COL1, FL_DARKER_COL1);

    flimage_enable_png();
    //skiold = flimage_load("logo_skiold.png")    
    skiold = flimage_load("/path/to/mypng/mypng.png");

    fl_end_form();
    fl_show_form(menu, FL_PLACE_MOUSE, FL_FULLBORDER, "Emulateur");
    flimage_display(skiold,  FL_ObjWin(canv));
    fl_do_forms(); 
    fl_hide_form(menu);
    fl_finish();

    return 0;
}