Drawing a bitmap in a class

Drawing a bitmap in a class

Navarrano

Member #13,776

November 2011

Hello,
I'm completly new to Allegro library so please be understanding.

I want to write a class which constructor will draw a bitmap on the display.

#include "main.h"
#include <allegro5\allegro.h>

using namespace std;

class Bouncer
{
public:
  ALLEGRO_BITMAP *bouncer;

  Bouncer::Bouncer( int a, int x, int y, int r, int g, int b );
  Bouncer::~Bouncer(void);
};

#include "Bouncer.h"

Bouncer::Bouncer( int a, int x, int y, int r, int g, int b )
{
  
  bouncer = al_create_bitmap(a,a);
  al_set_target_bitmap(bouncer);
  al_clear_to_color(al_map_rgb(r,g,b));

  al_draw_bitmap(bouncer, x, y, 0 );
}

Of course it is not working because my al_draw_bitmap(bouncer, x, y, 0) should work on my display backbuffer.
However, I don't know how to connect my class with a display created in my "main.cpp" file

ALLEGRO_DISPLAY *Window = NULL;
if( !(Window = al_create_display(640, 480) ) )
  {
    cerr << "Failed to create dipslay!" << endl;
    return -1;
  }

I tried solving it by putting external declaration in "main.h"

#include <allegro5\allegro.h>

 extern ALLEGRO_DISPLAY *Window;

but then I get unresolved external symbol error.

Thanks for Your help in advance.

Matthew Leverton

Supreme Loser

January 1999

You could do this:

ALLEGRO_STATE state;
al_store_state(&state, ALLEGRO_STATE_TARGET_BITMAP);

// change target bitmap, etc 

al_restore_state(&state);
al_draw_bitmap(bouncer, x, y, 0);

Or you could use al_set_target_backbuffer(al_get_current_display()).

--
RTFM | Follow Me on Google+ | I know 10 people

Edgar Reynaldo

Major Reynaldo

May 2007

You probably don't want to be doing all that in your constructor, and you don't need to make your ALLEGRO_DISPLAY* an extern one (by the way it is an unresolved symbol because you didn't define it in any source file - using extern only declares it).

Try separating out the functions involved :

#SelectExpand
  1class Bitmap {
  2private :
  3   ALLEGRO_BITMAP* bmp;
  4public :
  5   Bitmap(ALLEGRO_BITMAP* bitmap) : bmp(bitmap) {}
  6
  7   void ColorBitmap(int r, int g , int b , int a) {
  8      al_set_target_bitmap(bmp);
  9      al_clear_to_color(al_map_rgba(r,g,b,a));
 10   }
 11   void DrawBitmap() {
 12      al_draw_bitmap(bmp , 0 , 0 , 0);
 13   }
 14};
 15
 16// In main :
 17ALLEGRO_BITMAP* bouncer = al_create_bitmap(BOUNCER_W , BOUNCER_H);
 18Bitmap b(bouncer);
 19
 20b.ColorBitmap(0,0,64,255);
 21al_set_target_bitmap(al_get_backbuffer(display));
 22b.DrawBitmap();

Eagle and Allegro 5 binaries | Older Allegro 4 and 5 binaries | Allegro 5 compile guide
King Piccolo will make it so Then I could just flip it with some sweet, sweet matrix math. In either case, I’ll ride this wagon until the wheels fall off. Thanks to those that keep it running

Navarrano

Member #13,776

November 2011

Isn't

ALLEGRO_DISPLAY *Window = NULL;
if( !(Window = al_create_display(640, 480) ) )
  {
    cerr << "Failed to create dipslay!" << endl;
    return -1;
  }

a definition of Window?

Thanks a lot for the answers. They helped me a lot.
I guess I should stick to the idea of not creating everything in the constructor cuz this simple bitmap is intended to be a character in my game for the half-term examination so I will need lots of other methods =)

Edgar Reynaldo

Major Reynaldo

May 2007

Navarrano said:

Isn't

ALLEGRO_DISPLAY *Window = NULL;

a definition of Window?

Yes it is. Did you include main.h in main.cpp? And in Bouncer.cpp?

Navarrano

Member #13,776

November 2011

I have already deleted that source code but as far as I remember, I didn't include "main.h" in the "main.cpp" file but I did for "bouncer.h".

My programs were never complicated enough to use "extern" specificator so I'm not used to it.

For the future, I need to include such library with exter variables also in "main.cpp", right?

Edgar Reynaldo

Major Reynaldo

May 2007

Well, you should declare the variable as extern once in a header, and define it once in a source file that includes the header, and include that header whenever you need to access it.

Don't know why it didn't work for you, because you had Window declared as extern in your Bouncer.cpp through includes and you had it defined in main.cpp.