Using ALLEGRO_DISPLAY_CLOSE multiple times

no-reply@allegro.cc (mrmojorisin) — Sat, 13 Jun 2015 13:16:33 +0000

I am new in ALLEGRO PROGRAMMING and I was trying some code and I could not solve it... I looked over internet but there seems no solution OR i don't know what to search.

My CODE IS

#SelectExpand
  1int main()
  2{
al_init();
al_install_keyboard();
al_install_mouse();
al_init_primitives_addon();
al_set_new_display_flags(ALLEGRO_RESIZABLE);
ALLEGRO_DISPLAY *display= al_create_display(800,600);
ALLEGRO_EVENT_QUEUE *eventqueue = al_create_event_queue();
al_register_event_source(eventqueue, al_get_display_event_source(display));
al_register_event_source(eventqueue, al_get_mouse_event_source());
bool done = false;
while (!done)
{
  al_flip_display();
  al_draw_rectangle(60,60,180,180,al_map_rgb(122,233,121),4);
  ALLEGRO_EVENT events;
  al_wait_for_event(eventqueue, &events);
  if(events.type == ALLEGRO_EVENT_MOUSE_BUTTON_DOWN)
  {
    ALLEGRO_DISPLAY *display1 = al_create_display(400,300);
    al_flip_display;
    ALLEGRO_EVENT_QUEUE *eventqueue1 = al_create_event_queue();
    al_register_event_source(eventqueue1, al_get_display_event_source(display1));
    ALLEGRO_EVENT eventss;
    al_wait_for_event(eventqueue1, &eventss);
    if(eventss.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
    {
      al_destroy_display(display1);
      al_destroy_event_queue(eventqueue1);
    }
  }
  if(events.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
  {
    done = true;
  }
}
al_destroy_event_queue(eventqueue);
al_destroy_display(display);
return 0;
 41}

and My error message is in Attachment...

no-reply@allegro.cc (Thomas Fjellstrom) — Sat, 13 Jun 2015 17:58:53 +0000

What if you replace:

if(eventss.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
   al_destroy_display(display1);
   al_destroy_event_queue(eventqueue1);

with:

do {
  al_wait_for_event(eventqueue1, &eventss);
}
while(eventss.type != ALLEGRO_EVENT_CLOSE);
al_destory_event_source(eventqueue1);
al_destroy_display(display1);

no-reply@allegro.cc (mrmojorisin) — Sat, 13 Jun 2015 20:15:43 +0000

Thomas Fjellstrom - Tried it but same error message pops up when I close the display1 screen...

no-reply@allegro.cc (Edgar Reynaldo) — Sun, 14 Jun 2015 00:40:32 +0000

You're destroying the display twice, which makes it crash. Your event loop could use some work too. If you want to quit when you get an ALLEGRO_EVENT_DISPLAY_CLOSE mesage, just break out of your loop and then call your destruction functions :

#SelectExpand
  1int main(int argc , char** argv) {
  2
 /// Setup here
  4
 /// Main event loop here :
 do {
    if (redraw) {
       // redraw
       redraw = false;
    }
    ALLEGRO_EVENT ev;
    al_wait_for_event(queue , &ev);
    if (ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
       break;
    }
 } while (!al_is_event_queue_empty(queue));
 
 al_destroy_display(display);
 // ...
 return 0;
 21}

no-reply@allegro.cc (Thomas Fjellstrom) — Sun, 14 Jun 2015 02:36:13 +0000

Edgar Reynaldo said:

He's actually creating an entirely new display when hitting a mouse button, then (attempting) waiting for it to be closed, then waiting for the first to be closed.

no-reply@allegro.cc (Edgar Reynaldo) — Sun, 14 Jun 2015 04:00:57 +0000

Jeez. I need to get my eyes checked. Or learn how to read. Or something.

What is really happening is when you close display1 you try to draw to the target bitmap, which is the backbuffer of display1, which you just destroyed. That's why it crashes.

Set the target backbuffer before drawing to a display when you have multiple displays. al_set_target_backbuffer(display);

no-reply@allegro.cc (Thomas Fjellstrom) — Sun, 14 Jun 2015 22:51:17 +0000

Edgar Reynaldo said:

What is really happening is when you close display1 you try to draw to the target bitmap, which is the backbuffer of display1, which you just destroyed. That's why it crashes.

I guess I'm wrong, but I was under the impression that allegro unset the backbuffer when a display is destroyed. Maybe it does, but some things don't check that the backbuffer is null? That explains the 0xC access.

no-reply@allegro.cc (Edgar Reynaldo) — Mon, 15 Jun 2015 01:49:33 +0000

Well that's what GDB told me when I ran it through there. It said al_draw_prim crashed with a null target bitmap in a call to al_get_bitmap_flags :

#SelectExpand
  1Program received signal SIGSEGV, Segmentation fault.
  20x67701cd2 in al_get_bitmap_flags (bitmap=0x0) at C:\mingw\LIBS\A5GIT\allegro\src\bitmap.c:324
  3324        if (bitmap->parent)
  4(gdb) bt
  5#0  0x67701cd2 in al_get_bitmap_flags (bitmap=0x0) at C:\mingw\LIBS\A5GIT\allegro\src\bitmap.c:324
  6#1  0x67801047 in al_draw_prim (vtxs=0x22fc80, decl=0x0, texture=0x0, start=0, end=10, type=4) at C:\mingw\LIBS\A5GIT\allegro\addons\primitives\primitives.c:86
  7#2  0x677f2559 in al_draw_rectangle (x1=60, y1=60, x2=180, y2=180, color=..., thickness=4) at C:\mingw\LIBS\A5GIT\allegro\addons\primitives\high_primitives.c:382
  8#3  0x004017e7 in main () at Test.cpp:23
  9(gdb) frame 1
 10#1  0x67801047 in al_draw_prim (vtxs=0x22fc80, decl=0x0, texture=0x0, start=0, end=10, type=4) at C:\mingw\LIBS\A5GIT\allegro\addons\primitives\primitives.c:86
 1186         if (al_get_bitmap_flags(target) & ALLEGRO_MEMORY_BITMAP ||
 12(gdb) l
 1381
 1482         /* In theory, if we ever get a camera concept for this addon, the transformation into
 1583          * view space should occur here
 1684          */
 1785
 1886         if (al_get_bitmap_flags(target) & ALLEGRO_MEMORY_BITMAP ||
 1987             (texture && al_get_bitmap_flags(texture) & ALLEGRO_MEMORY_BITMAP) ||
 2088             _al_pixel_format_is_compressed(al_get_bitmap_format(target))) {
 2189            ret =  _al_draw_prim_soft(texture, vtxs, decl, start, end, type);
 2290         } else {
 23(gdb)

I used pretty much the exact code he did (aside from a typo and missing includes) to cause the segfault :

#SelectExpand
  1
  2
  3#include "allegro5/allegro.h"
  4#include "allegro5/allegro_primitives.h"
  5
  6
  7
  8int main()
  9{
al_init();
al_install_keyboard();
al_install_mouse();
al_init_primitives_addon();
al_set_new_display_flags(ALLEGRO_RESIZABLE);
ALLEGRO_DISPLAY *display= al_create_display(800,600);
ALLEGRO_EVENT_QUEUE *eventqueue = al_create_event_queue();
al_register_event_source(eventqueue, al_get_display_event_source(display));
al_register_event_source(eventqueue, al_get_mouse_event_source());
bool done = false;
while (!done)
{
  al_flip_display();
  al_draw_rectangle(60,60,180,180,al_map_rgb(122,233,121),4);
  ALLEGRO_EVENT events;
  al_wait_for_event(eventqueue, &events);
  if(events.type == ALLEGRO_EVENT_MOUSE_BUTTON_DOWN)
  {
    ALLEGRO_DISPLAY *display1 = al_create_display(400,300);
    al_flip_display();
    ALLEGRO_EVENT_QUEUE *eventqueue1 = al_create_event_queue();
    al_register_event_source(eventqueue1, al_get_display_event_source(display1));
    ALLEGRO_EVENT eventss;
    al_wait_for_event(eventqueue1, &eventss);
    if(eventss.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
    {
      al_destroy_display(display1);
      al_destroy_event_queue(eventqueue1);
    }
  }
  if(events.type == ALLEGRO_EVENT_DISPLAY_CLOSE)
  {
    done = true;
  }
}
al_destroy_event_queue(eventqueue);
al_destroy_display(display);
return 0;
 48}