How to correctly implement an image using GLFW and Cairo

GLFW_Cairo_image.c

/*
 *
 */

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <cairo/cairo.h>
#include <cairo/cairo-xlib.h>

#include <GLFW/glfw3.h>
#define GLFW_EXPOSE_NATIVE_X11
#include <GLFW/glfw3native.h>

#define UNUSED( x ) ( ( void )( x ) )

typedef struct
{
   GLFWwindow *      win;
   int               width;
   int               height;
   Display *         xdpy;
   Window            xwin;
   Visual *          vis;
   cairo_surface_t * surface;
   cairo_t *         cr;
   cairo_surface_t * image;
} GLFW_Cairo;

static GLFW_Cairo gl;

static void key_callback( GLFWwindow * window, int key, int scancode, int action, int mods );

int main()
{
   memset( &gl, 0, sizeof( gl ) );
   int width = 0, height = 0;
   int w, h;

   if( ! glfwInit() )
   {
      glfwTerminate();
      exit( EXIT_FAILURE );
   }

   glfwWindowHint( GLFW_CLIENT_API, GLFW_NO_API );

   gl.win = glfwCreateWindow( 720, 512, "GLFW .AND. Cairo", NULL, NULL );
   if( ! gl.win )
   {
      glfwTerminate();
      exit( EXIT_FAILURE );
   }

   glfwSwapInterval( 1 );

   gl.xdpy = glfwGetX11Display();
   gl.xwin = glfwGetX11Window( gl.win );

   gl.vis  = DefaultVisual( gl.xdpy, DefaultScreen( gl.xdpy ) );
   if( ! gl.vis )
   {
      glfwTerminate();
      exit( EXIT_FAILURE );
   }

   glfwGetFramebufferSize( gl.win, &gl.width, &gl.height );
   gl.surface  = cairo_xlib_surface_create( gl.xdpy, gl.xwin, gl.vis, gl.width, gl.height );

   gl.cr = cairo_create( gl.surface );
   if( ! gl.cr )
   {
      glfwTerminate();
      exit( EXIT_FAILURE );
   }

   glfwSetKeyCallback( gl.win, key_callback );

   while( ! glfwWindowShouldClose( gl.win ) )
   {
      glfwGetFramebufferSize( gl.win, &gl.width, &gl.height );
      cairo_xlib_surface_set_size( gl.surface, gl.width, gl.height );

      cairo_push_group( gl.cr );

      if( width != gl.width || height != gl.height )
      {
      cairo_set_source_rgb( gl.cr, 0.0, 0.0, 0.0 );
      cairo_set_operator( gl.cr, CAIRO_OPERATOR_SOURCE );
      cairo_paint( gl.cr );
      //---
      gl.image = cairo_image_surface_create_from_png( "cairo.png" );
      w = cairo_image_surface_get_width( gl.image );
      h = cairo_image_surface_get_height( gl.image );

      cairo_scale( gl.cr, 80.0 / w, 80.0 / h );

      cairo_set_source_surface( gl.cr, gl.image, 0, 0 );
      cairo_paint( gl.cr );

      width  = gl.width;
      height = gl.height;
      //---
      }
      cairo_pop_group_to_source( gl.cr );
      cairo_paint( gl.cr );
      cairo_surface_flush( gl.surface );

      glfwSwapBuffers( gl.win );
      glfwPollEvents();
   }
   cairo_surface_destroy( gl.image );
   cairo_destroy( gl.cr );
   cairo_surface_finish( gl.surface );
   cairo_surface_destroy( gl.surface );

   cairo_surface_destroy( gl.image );

   glfwDestroyWindow( gl.win );

   glfwTerminate();
   exit( EXIT_SUCCESS );
}

static void key_callback( GLFWwindow * window, int key, int scancode, int action, int mods )
{
   UNUSED( scancode );
   UNUSED( mods );

   if( action == GLFW_PRESS )
   {
      return;
   }

   switch( key )
   {
      case GLFW_KEY_ESCAPE:
      {
         glfwSetWindowShouldClose( window, GLFW_TRUE );
         break;
      }
   }
}