Allegro + OpenGL http://www.allegro.cc/forums/view/610579 Allegro.cc Forum Thread matthew@allegro.cc (Matthew Leverton) Mon, 09 Jul 2012 00:47:43 +0000

Hey guys,

I'm working on a 3-D OpenGL game and am using Allegro. However, I have no idea how to do this (with Allegro, that is, I understand OpenGL).

Here's some code:

#SelectExpand
1#include <allegro5/allegro.h> 2#include <allegro5/allegro_opengl.h> 3 4int 5main (void) 6{ 7 al_init (); 8 9 al_set_new_display_flags (ALLEGRO_OPENGL); 10 11 ALLEGRO_DISPLAY *display = al_create_display (800, 600); 12 al_set_current_opengl_context (display); 13 14 ALLEGRO_EVENT_QUEUE *event_queue = al_create_event_queue (); 15 al_register_event_source (event_queue, al_get_display_event_source (display)); 16 17 glEnable (GL_DEPTH_TEST); 18 glViewport (0, 0, 800, 600); 19 20 for (;;) 21 { 22 ALLEGRO_EVENT event; 23 while (al_get_next_event (event_queue, &event)) 24 if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) 25 return EXIT_SUCCESS; 26 27 glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 28 29 glBegin (GL_POLYGON); 30 glColor3f (1.0, 1.0, 1.0); 31 glVertex3f (0.5, -0.5, 0.5); 32 glVertex3f (0.5, 0.5, 0.5); 33 glVertex3f (-0.5, 0.5, 0.5); 34 glVertex3f (-0.5, -0.5, 0.5); 35 glEnd (); 36 37 glBegin (GL_POLYGON); 38 glColor3f (1.0, 0.0, 1.0); 39 glVertex3f (0.5, -0.5, -0.5); 40 glVertex3f (0.5, 0.5, -0.5); 41 glVertex3f (0.5, 0.5, 0.5); 42 glVertex3f (0.5, -0.5, 0.5); 43 glEnd (); 44 45 glBegin (GL_POLYGON); 46 glColor3f (0.0, 1.0, 0.0); 47 glVertex3f (-0.5, -0.5, 0.5); 48 glVertex3f (-0.5, 0.5, 0.5); 49 glVertex3f (-0.5, 0.5, -0.5); 50 glVertex3f (-0.5, -0.5, -0.5); 51 glEnd (); 52 53 glBegin (GL_POLYGON); 54 glColor3f (0.0, 0.0, 1.0); 55 glVertex3f (0.5, 0.5, 0.5); 56 glVertex3f (0.5, 0.5, -0.5); 57 glVertex3f (-0.5, 0.5, -0.5); 58 glVertex3f (-0.5, 0.5, 0.5); 59 glEnd (); 60 61 glBegin (GL_POLYGON); 62 glColor3f (1.0, 0.0, 0.0); 63 glVertex3f (0.5, -0.5, -0.5); 64 glVertex3f (0.5, -0.5, 0.5); 65 glVertex3f (-0.5, -0.5, 0.5); 66 glVertex3f (-0.5, -0.5, -0.5); 67 glEnd (); 68 69 glFlush (); 70 al_flip_display (); 71 } 72} 73 74/* vim:set ts=8 sts=2 sw=2 noet: */

Pardon how hideous it is, lacking any form of error checking and all. I'm just trying to figure out how Allegro and OpenGL work together. I'm sure a few of those calls aren't even necessary, but I've been trying everything to get something other than a blank, black screen.

Any help would be greatly, GREATLY appreciated.
- Luiji

]]> no-reply@allegro.cc (Luiji99) Fri, 06 Jul 2012 09:59:55 +0000

One thing that comes to mind, I think Allegro does not set a depth buffer, check this out to set one:
http://www.liballeg.org/a5docs/refman/display.html#al_set_new_display_option

ALLEGRO_DEPTH_SIZE

How many depth buffer (z-buffer) bits to use.

You might also want to check out:
ex_opengl.c

]]> no-reply@allegro.cc (jmasterx) Fri, 06 Jul 2012 10:06:19 +0000

Hm, I've modified the code to set the ALLEGRO_DEPTH_SIZE to 30 (sort of a random number, I figured it'd be big enough to play with later):

#SelectExpand
1#include <err.h> 2 3#include <allegro5/allegro.h> 4#include <allegro5/allegro_opengl.h> 5 6int 7main (void) 8{ 9 if (!al_init ()) 10 errx (1, "failed to initialize allegro"); 11 12 al_set_new_display_flags (ALLEGRO_OPENGL); 13 al_set_new_display_option (ALLEGRO_DEPTH_SIZE, 30, ALLEGRO_REQUIRE); 14 15 ALLEGRO_DISPLAY *display = al_create_display (800, 600); 16 if (!display) 17 errx (1, "failed to create display"); 18 19 al_set_current_opengl_context (display); 20 21 ALLEGRO_EVENT_QUEUE *event_queue = al_create_event_queue (); 22 if (!event_queue) 23 errx (1, "failed to create event queue"); 24 25 al_register_event_source (event_queue, al_get_display_event_source (display)); 26 27 glEnable (GL_DEPTH_TEST); 28 glViewport (0, 0, 800, 600); 29 30 for (;;) 31 { 32 ALLEGRO_EVENT event; 33 while (al_get_next_event (event_queue, &event)) 34 if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) 35 { 36 al_destroy_event_queue (event_queue); 37 return EXIT_SUCCESS; 38 } 39 40 glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 41 42 glBegin (GL_POLYGON); 43 glColor3f (1.0, 1.0, 1.0); 44 glVertex3f (0.5, -0.5, 0.5); 45 glVertex3f (0.5, 0.5, 0.5); 46 glVertex3f (-0.5, 0.5, 0.5); 47 glVertex3f (-0.5, -0.5, 0.5); 48 glEnd (); 49 50 glBegin (GL_POLYGON); 51 glColor3f (1.0, 0.0, 1.0); 52 glVertex3f (0.5, -0.5, -0.5); 53 glVertex3f (0.5, 0.5, -0.5); 54 glVertex3f (0.5, 0.5, 0.5); 55 glVertex3f (0.5, -0.5, 0.5); 56 glEnd (); 57 58 glBegin (GL_POLYGON); 59 glColor3f (0.0, 1.0, 0.0); 60 glVertex3f (-0.5, -0.5, 0.5); 61 glVertex3f (-0.5, 0.5, 0.5); 62 glVertex3f (-0.5, 0.5, -0.5); 63 glVertex3f (-0.5, -0.5, -0.5); 64 glEnd (); 65 66 glBegin (GL_POLYGON); 67 glColor3f (0.0, 0.0, 1.0); 68 glVertex3f (0.5, 0.5, 0.5); 69 glVertex3f (0.5, 0.5, -0.5); 70 glVertex3f (-0.5, 0.5, -0.5); 71 glVertex3f (-0.5, 0.5, 0.5); 72 glEnd (); 73 74 glBegin (GL_POLYGON); 75 glColor3f (1.0, 0.0, 0.0); 76 glVertex3f (0.5, -0.5, -0.5); 77 glVertex3f (0.5, -0.5, 0.5); 78 glVertex3f (-0.5, -0.5, 0.5); 79 glVertex3f (-0.5, -0.5, -0.5); 80 glEnd (); 81 82 glFlush (); 83 al_flip_display (); 84 } 85} 86 87/* vim:set ts=8 sts=2 sw=2 noet: */

However, now my program aborts with "cube: failed to create display". It seems that Allegro can't set the z-depth. I don't think it's anything wrong with my hardware/drivers, though, since GlxGears runs perfectly and I'm pretty sure that it uses a z-buffer, too.

Thanks,
- L

]]> no-reply@allegro.cc (Luiji99) Fri, 06 Jul 2012 22:51:27 +0000

I'm pretty sure z buffer sizes are limited to 16, 24 or 32 bits, since it's bits per element, it might have been better if they'd specified how many bytes per element, not bits.

]]> no-reply@allegro.cc (Arthur Kalliokoski) Fri, 06 Jul 2012 22:57:28 +0000

Ah, I totally misunderstood what that field did. Anyway...

#SelectExpand
1#include <err.h> 2 3#include <allegro5/allegro.h> 4#include <allegro5/allegro_opengl.h> 5 6int 7main (void) 8{ 9 if (!al_init ()) 10 errx (1, "failed to initialize allegro"); 11 12 al_set_new_display_flags (ALLEGRO_OPENGL); 13 al_set_new_display_option (ALLEGRO_DEPTH_SIZE, 16, ALLEGRO_REQUIRE); 14 15 ALLEGRO_DISPLAY *display = al_create_display (300, 300); 16 if (!display) 17 errx (1, "failed to create display"); 18 19 ALLEGRO_EVENT_QUEUE *event_queue = al_create_event_queue (); 20 if (!event_queue) 21 errx (1, "failed to create event queue"); 22 23 al_register_event_source (event_queue, al_get_display_event_source (display)); 24 25 glEnable (GL_DEPTH_TEST); 26 glClearColor (0.5, 0.5, 0.5, 1.0); 27 28 for (;;) 29 { 30 ALLEGRO_EVENT event; 31 while (al_get_next_event (event_queue, &event)) 32 if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) 33 { 34 al_destroy_event_queue (event_queue); 35 return EXIT_SUCCESS; 36 } 37 38 glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 39 glLoadIdentity (); 40 41 glRotatef (45, 1, 0, 0); 42 glRotatef (45, 0, 1, 0); 43 44 glBegin(GL_POLYGON); 45 glColor3f(1, 0, 0 ); glVertex3f( 0.5, -0.5, -0.5); 46 glColor3f(0, 1, 0 ); glVertex3f( 0.5, 0.5, -0.5); 47 glColor3f(0, 0, 1 ); glVertex3f(-0.5, 0.5, -0.5); 48 glColor3f(1, 0, 1 ); glVertex3f(-0.5, -0.5, -0.5); 49 glEnd(); 50 51 glBegin (GL_POLYGON); 52 glColor3f (1, 1, 1); 53 glVertex3f (0.5, -0.5, 0.5); 54 glVertex3f (0.5, 0.5, 0.5); 55 glVertex3f (-0.5, 0.5, 0.5); 56 glVertex3f (-0.5, -0.5, 0.5); 57 glEnd (); 58 59 glBegin (GL_POLYGON); 60 glColor3f (1, 0, 1); 61 glVertex3f (0.5, -0.5, -0.5); 62 glVertex3f (0.5, 0.5, -0.5); 63 glVertex3f (0.5, 0.5, 0.5); 64 glVertex3f (0.5, -0.5, 0.5); 65 glEnd (); 66 67 glBegin (GL_POLYGON); 68 glColor3f (0, 1, 0); 69 glVertex3f (-0.5, -0.5, 0.5); 70 glVertex3f (-0.5, 0.5, 0.5); 71 glVertex3f (-0.5, 0.5, -0.5); 72 glVertex3f (-0.5, -0.5, -0.5); 73 glEnd (); 74 75 glBegin (GL_POLYGON); 76 glColor3f (0, 0, 1); 77 glVertex3f (0.5, 0.5, 0.5); 78 glVertex3f (0.5, 0.5, -0.5); 79 glVertex3f (-0.5, 0.5, -0.5); 80 glVertex3f (-0.5, 0.5, 0.5); 81 glEnd (); 82 83 glBegin (GL_POLYGON); 84 glColor3f (1, 0, 0); 85 glVertex3f (0.5, -0.5, -0.5); 86 glVertex3f (0.5, -0.5, 0.5); 87 glVertex3f (-0.5, -0.5, 0.5); 88 glVertex3f (-0.5, -0.5, -0.5); 89 glEnd (); 90 91 glFlush (); 92 al_flip_display (); 93 } 94} 95 96/* vim:set ts=8 sts=2 sw=2 noet: */

Played around with it a bit more. The display creates now, but all I see is grey (I set the clear color just to make sure that the OpenGL calls were working).

This code is essentially a GLUT equivalent that I'm basing this off of, and it works perfectly. It seems to be a problem with Allegro, or at least a difference in what can be assumed from each library:

#SelectExpand
1#include <GL/glut.h> 2 3static void 4display () 5{ 6 glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 7 8 glLoadIdentity (); 9 10 glRotatef (45, 1, 0, 0); 11 glRotatef (45, 0, 1, 0); 12 13 glBegin (GL_POLYGON); 14 glColor3f (1, 0, 0); 15 glVertex3f (0.5, -0.5, -0.5); 16 glColor3f (0, 1, 0); 17 glVertex3f (0.5, 0.5, -0.5); 18 glColor3f (0, 0, 1); 19 glVertex3f (-0.5, 0.5, -0.5); 20 glColor3f (1, 0, 1); 21 glVertex3f (-0.5, -0.5, -0.5); 22 glEnd (); 23 24 glBegin (GL_POLYGON); 25 glColor3f (1, 1, 1); 26 glVertex3f (0.5, -0.5, 0.5); 27 glVertex3f (0.5, 0.5, 0.5); 28 glVertex3f (-0.5, 0.5, 0.5); 29 glVertex3f (-0.5, -0.5, 0.5); 30 glEnd (); 31 32 glBegin (GL_POLYGON); 33 glColor3f (1, 0, 1); 34 glVertex3f (0.5, -0.5, -0.5); 35 glVertex3f (0.5, 0.5, -0.5); 36 glVertex3f (0.5, 0.5, 0.5); 37 glVertex3f (0.5, -0.5, 0.5); 38 glEnd (); 39 40 glBegin (GL_POLYGON); 41 glColor3f (0, 1, 0); 42 glVertex3f (-0.5, -0.5, 0.5); 43 glVertex3f (-0.5, 0.5, 0.5); 44 glVertex3f (-0.5, 0.5, -0.5); 45 glVertex3f (-0.5, -0.5, -0.5); 46 glEnd (); 47 48 glBegin (GL_POLYGON); 49 glColor3f (0, 0, 1); 50 glVertex3f (0.5, 0.5, 0.5); 51 glVertex3f (0.5, 0.5, -0.5); 52 glVertex3f (-0.5, 0.5, -0.5); 53 glVertex3f (-0.5, 0.5, 0.5); 54 glEnd (); 55 56 glBegin (GL_POLYGON); 57 glColor3f (1, 0, 0); 58 glVertex3f (0.5, -0.5, -0.5); 59 glVertex3f (0.5, -0.5, 0.5); 60 glVertex3f (-0.5, -0.5, 0.5); 61 glVertex3f (-0.5, -0.5, -0.5); 62 glEnd (); 63 64 glFlush (); 65 glutSwapBuffers (); 66} 67 68int 69main (int argc, char *argv[]) 70{ 71 glutInit (&argc, argv); 72 glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH); 73 glutCreateWindow (argv[0]); 74 75 glEnable (GL_DEPTH_TEST); 76 glClearColor (0.5, 0.5, 0.5, 1.0); 77 78 glutDisplayFunc (display); 79 80 glutMainLoop (); 81 82 return 0; 83}

==================== EDIT ====================

I did it! All I had to do was add "glMatrixMode (GL_PROJECTION)", which apparently GLUT automatically does and Allegro does not. It's kind of an odd difference, but I have a cube and that's satisfying!!

Thanks for the help,
- L

]]> no-reply@allegro.cc (Luiji99) Fri, 06 Jul 2012 23:51:28 +0000

Allegro by default sets up a 2d "Allegro" matrix, so when you draw with allegro functions, things appear to work with a plain old 2d coordinate space with the top left being 0,0.

]]> no-reply@allegro.cc (Thomas Fjellstrom) Sat, 07 Jul 2012 00:01:34 +0000

Ah.

Just wondering, might it be useful to include something like this in Allegro? I can clean this example up a bit...the resulting cube is pretty cool. It also takes advantage of ALLEGRO_TIMER, which is nice.

Thanks,
- L

]]> no-reply@allegro.cc (Luiji99) Sun, 08 Jul 2012 03:15:09 +0000

If its showing stuff that existing examples don't show, I don't see why not.

]]> no-reply@allegro.cc (Thomas Fjellstrom) Sun, 08 Jul 2012 04:31:28 +0000

Unlike the current OpenGL example, this one actually renders 3-D. I don't know what the Direct3D example shows...

I think it's also just pretty fun to run in the background to make you look cool in front of people looking over your shoulder. =)

#SelectExpand
1#include <allegro5/allegro.h> 2#include <allegro5/allegro_opengl.h> 3 4#include "common.c" 5 6int main(void) 7{ 8 ALLEGRO_DISPLAY *display; 9 ALLEGRO_TIMER *timer; 10 ALLEGRO_EVENT_QUEUE *event_queue; 11 int rotation = 0; 12 13 if (!al_init()) 14 abort_example("failed to initialize allegro"); 15 16 al_set_new_display_flags(ALLEGRO_OPENGL); 17 al_set_new_display_option(ALLEGRO_DEPTH_SIZE, 16, ALLEGRO_REQUIRE); 18 19 display = al_create_display(600, 600); 20 if (!display) 21 abort_example("failed to create display"); 22 23 timer = al_create_timer(ALLEGRO_BPS_TO_SECS(180)); 24 if (!timer) 25 abort_example("failed to create timer"); 26 27 event_queue = al_create_event_queue(); 28 if (!event_queue) 29 abort_example("failed to create event queue"); 30 31 al_register_event_source(event_queue, al_get_display_event_source(display)); 32 al_register_event_source(event_queue, al_get_timer_event_source(timer)); 33 34 glEnable(GL_DEPTH_TEST); 35 glClearColor(0.5, 0.5, 0.5, 1.0); 36 glMatrixMode(GL_PROJECTION); 37 38 al_start_timer(timer); 39 40 for (;;) { 41 ALLEGRO_EVENT event; 42 while (al_get_next_event(event_queue, &event)) 43 if (event.type == ALLEGRO_EVENT_TIMER) { 44 rotation = rotation == 359 ? 0 : rotation + 1; 45 } 46 else if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) { 47 al_destroy_event_queue(event_queue); 48 al_destroy_timer(timer); 49 al_destroy_display(display); 50 return EXIT_SUCCESS; 51 } 52 53 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 54 glLoadIdentity(); 55 56 glRotatef(rotation, 1, 0, 0); 57 glRotatef(rotation, 0, 1, 0); 58 59 glBegin(GL_POLYGON); 60 glColor3f(1, 0, 0); 61 glVertex3f(0.5, -0.5, -0.5); 62 glColor3f(0, 1, 0); 63 glVertex3f(0.5, 0.5, -0.5); 64 glColor3f(0, 0, 1); 65 glVertex3f(-0.5, 0.5, -0.5); 66 glColor3f(1, 0, 1); 67 glVertex3f(-0.5, -0.5, -0.5); 68 glEnd(); 69 70 glBegin(GL_POLYGON); 71 glColor3f(1, 1, 1); 72 glVertex3f(0.5, -0.5, 0.5); 73 glVertex3f(0.5, 0.5, 0.5); 74 glVertex3f(-0.5, 0.5, 0.5); 75 glVertex3f(-0.5, -0.5, 0.5); 76 glEnd(); 77 78 glBegin(GL_POLYGON); 79 glColor3f(1, 0, 1); 80 glVertex3f(0.5, -0.5, -0.5); 81 glVertex3f(0.5, 0.5, -0.5); 82 glVertex3f(0.5, 0.5, 0.5); 83 glVertex3f(0.5, -0.5, 0.5); 84 glEnd(); 85 86 glBegin(GL_POLYGON); 87 glColor3f(0, 1, 0); 88 glVertex3f(-0.5, -0.5, 0.5); 89 glVertex3f(-0.5, 0.5, 0.5); 90 glVertex3f(-0.5, 0.5, -0.5); 91 glVertex3f(-0.5, -0.5, -0.5); 92 glEnd(); 93 94 glBegin(GL_POLYGON); 95 glColor3f(0, 0, 1); 96 glVertex3f(0.5, 0.5, 0.5); 97 glVertex3f(0.5, 0.5, -0.5); 98 glVertex3f(-0.5, 0.5, -0.5); 99 glVertex3f(-0.5, 0.5, 0.5); 100 glEnd(); 101 102 glBegin(GL_POLYGON); 103 glColor3f(1, 0, 0); 104 glVertex3f(0.5, -0.5, -0.5); 105 glVertex3f(0.5, -0.5, 0.5); 106 glVertex3f(-0.5, -0.5, 0.5); 107 glVertex3f(-0.5, -0.5, -0.5); 108 glEnd(); 109 110 al_flip_display(); 111 } 112} 113 114/* vim: set sts=3 sw=3 et: */

I think that under the Allegro.cc terms you guys now own that code or something. I don't exactly know how that provision works, I still own the Copyright, don't I? Anyway, for the wonders of legal clarity, I hereby give the Allegro developers permission to redistribute that code under any license they want, with or without modification. I PROVIDE NOT WARRANTY AT ALL.

]]> no-reply@allegro.cc (Luiji99) Sun, 08 Jul 2012 23:54:46 +0000
Luiji99 said:

Unlike the current OpenGL example, this one actually renders 3-D.

The ex_gldepth example shows interlocking 3D pyramids with textures.

]]> no-reply@allegro.cc (Arthur Kalliokoski) Sun, 08 Jul 2012 23:57:31 +0000

Ah, well then my example doesn't really add anything new. I like the way mine looks better, though. =P

The current example actually has more stuff, too, such as drawing graphical textures onto the polygons.

Thanks,
- L

]]> no-reply@allegro.cc (Luiji99) Mon, 09 Jul 2012 00:47:43 +0000