Rendering A Hot Air Balloon

Scooter

Hi all:

I had an idea the other day: make a hot air balloon

using allegro and opengl. Do you think this would be

a project a newbie could accomplish? If so, where would

one begin? I have had to give up on many things because

it got too difficult for me! This would be great if it

could be done!

Thanks for your time.

bamccaig

Set the bar low to start. A hot air balloon could be as simple as a circle with a square beneath it, or a sphere and a cube if 3D.

Note: Allegro doesn't really help you drawing 3D things. You need to do that with GL directly. Allegro will just initialize things for you I think.

After you've got a very simple program working you can expand upon it to make it better, piece by piece. If you aim too high you won't get anything done.

Scooter

Hi bamccaig:

Great idea! If I start with a sphere, bring the bottom of the

sphere down, narrow it a bit I would have the shape I need.

Is there a way to do such a thing in opengl? Just a thought.

Thanks

bamccaig

I'm afraid OpenGL is far too complicated to learn it from questions and answers on a messaging board. If you don't know it yet you're going to have to learn it first. Put the hot air balloon idea on a shelf, and start by completing an OpenGL tutorial or two. Once you've got a simple program running you can try Googling for things that you think you'll need for the hot air balloon, and try to figure out how to do it. If you have trouble getting something to work you can post here, but don't expect us to do your homework for you. That's not how the Internet works. I can't help anyway because I myself haven't gone past the tutorial step.

Scooter

Hi bamccaig:

Sorry, didn't mean to upset you!

Have a great day!

bamccaig

I'm not upset. I'm just trying to steer you in the right direction.

Edgar Reynaldo

Step 1) Decide the technical requirements of what you want to do.
Step 2) Decide what is the best way to accomplish that
Step 3) Implement a very basic version to start
Step 4) Improve
Step 5) Repeat step 4
Step 6) Decide if you're satisfied with where you're at.
Step 6a) Go back to 1
Step 7) $PROFIT$

For instance, here's a hot air balloon I drew by accident. Allegro is more than capable of drawing a balloon as a polygon, a set of lines, etc... You don't specifically need to know OpenGL to do it.

http://members.allegro.cc/EdgarReynaldo/previews/Spiraloid/Balloon1.html

{"name":"Balloon1.png","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/d\/c\/dca6d415a73ea6eb425fd585553435af.png","w":1024,"h":768,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/d\/c\/dca6d415a73ea6eb425fd585553435af"}

EDIT
Technically you can think of a balloon as a series of discs layered together.

Once you have that, you can try to texture it.

Scooter

Hi Edgar:

Thanks for the reply. It has been awhile, hope all is well!

I have downloaded 2 files: balloon.jpg and section.png. The

balloon file will show you what I am trying to duplicate. There

are 10 sections to the balloon. The section file shows one

of the 10 sections without the birds. My problem is the section

has to be fitted to the balloon shape. That is my problem. What

is the best way to do this? If you have any questions let me know.

Thanks!

Edgar Reynaldo

Are you planning on a 2D balloon or a 3D one?

You need the vertices, and the texture coordinates.

From something like an .obj or some kind of model file.

Then you can draw with allegro or opengl.

Scooter

Hi Edgar:

Oh, it must be 3D in opengl! As far as the .obj file: do I need to

do the balloon in Blender and then import to opengl? I hope not!

Thanks!

Edgar Reynaldo

Make the strips horizontal. Vertical will only give you pain. Break them up into a band. Take a disc and make a bracelet. The outside of the bracelet is the band which you render in opengl. You still don't need OpenGL to do this, as allegro can do it for you.

al_draw_prim

hint
It can be done by hand with a little radial trigonometry in 3D.

Align it down the axis, and every band is just a circle of different radius connected to to the previous and next strip.

MikiZX

I've been playing with the problem of creating a hot air balloon in code and.. well.. maybe it helps:
(done using gluCylinder and gluSphere)

#SelectExpand
   1#include <stdio.h>
   2#include <math.h>
   3#include <allegro5/allegro.h>
   4#include "allegro5/allegro_primitives.h"
   5#include <allegro5/allegro_opengl.h>
   6#include <GL/glu.h>
   7
   8
   9const float FPS = 60;
  10
  11ALLEGRO_DISPLAY *display = NULL;
  12ALLEGRO_EVENT_QUEUE *event_queue = NULL;
  13ALLEGRO_TIMER *timer1 = NULL;
  14
  15bool redraw = true;
  16
  17double lightangle = 0.0;
  18GLUquadricObj *quadric = NULL;
  19
  20// isolating cleanup code in a single function because we use this code many times
  21// doing this will keep the rest of the source code easier to read
  22void close_and_exit()
  23{
  24   if (quadric) gluDeleteQuadric(quadric);
  25   if (timer1) al_destroy_timer(timer1);
  26   if (display) al_destroy_display(display);
  27   if (event_queue) al_destroy_event_queue(event_queue);
  28   al_uninstall_system();
  29   exit(0);
  30}
  31
  32// the program execution starts here with 'main' function
  33int main(int argc, char **argv){
  34
  35   // here we initialize different parts of Allegro
  36   if(!al_init()) {
  37      fprintf(stderr, "failed to initialize allegro!\n");
  38      return -1;
  39   }
  40
  41   al_init_primitives_addon();
  42   al_set_new_display_option(ALLEGRO_DEPTH_SIZE , ALLEGRO_DONTCARE  , 16);
  43   al_set_new_display_flags(ALLEGRO_OPENGL );
  44   display = al_create_display(640, 480);
  45   if(!display) {
  46      fprintf(stderr, "failed to create display!\n");
  47      close_and_exit();
  48   }
  49
  50   if (!al_install_keyboard())
  51       {
  52       fprintf(stderr, "Error installing keyboard.\n");
  53       close_and_exit();
  54       }
  55
  56   event_queue = al_create_event_queue();
  57   if(!event_queue) {
  58      fprintf(stderr, "failed to create event_queue!\n");
  59      close_and_exit();
  60   }
  61
  62   timer1 = al_create_timer(1.0 / FPS);
  63   if(!timer1) {
  64      fprintf(stderr, "failed to create timer!\n");
  65      close_and_exit();
  66   }
  67
  68   al_register_event_source(event_queue, al_get_keyboard_event_source());
  69
  70   al_register_event_source(event_queue, al_get_display_event_source(display));
  71
  72   al_register_event_source(event_queue, al_get_timer_event_source(timer1));
  73
  74   al_start_timer(timer1);
  75
  76glEnable(GL_DEPTH_TEST);
  77glDisable(GL_CULL_FACE);
  78glEnable(GL_LIGHTING);
  79quadric = gluNewQuadric();
  80   while(1)
  81   {
  82      ALLEGRO_EVENT ev;
  83      al_wait_for_event(event_queue, &ev);
  84
  85      if(ev.type == ALLEGRO_EVENT_TIMER) {
  86         redraw = true;
  87      }
  88
  89      if(ev.type == ALLEGRO_EVENT_KEY_DOWN) {
  90
  91         if (ev.keyboard.keycode==ALLEGRO_KEY_ESCAPE)
  92            close_and_exit();
  93      }
  94
  95
  96      if(ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
  97         break;
  98      }
  99
 100      if(redraw && al_is_event_queue_empty(event_queue))
 101       {
 102       redraw = false;
 103       al_set_target_backbuffer(display);
 104       al_clear_to_color(al_map_rgb(0,50,140));
 105       glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 106       glMatrixMode(GL_PROJECTION);
 107       glLoadIdentity();
 108       gluPerspective(90.0, (GLdouble)640.0 / (GLdouble)480.0, 1.0, 2000.0);
 109
 110       glMatrixMode(GL_MODELVIEW);
 111       glLoadIdentity();
 112       gluLookAt(0.0f, 0.0f, -100.0f, 0.0f, 0.0f, 1.0f, 0.0, 1.0f, 0.0f);
 113
 114       GLfloat light0_pos[] = {50.0, 50.0, -50.0, 1.0};
 115       GLfloat light0_color[] = {0.01, 0.01, 0.01, 0.0};
 116       GLfloat light1_pos[] = {10.0, 35.0, -10.0, 1.0};
 117       GLfloat light1_color[] = {1.0, 0.80, 0.65, 0.0};
 118       light1_pos[0]=cos(lightangle/10.0)*4000.0;
 119       light1_pos[2]=sin(lightangle/10.0)*4000.0;
 120       lightangle+=0.01;
 121       glLightfv( GL_LIGHT0,GL_POSITION,light0_pos);
 122       glLightfv( GL_LIGHT0,GL_DIFFUSE,light1_color);
 123       glLightfv( GL_LIGHT0,GL_AMBIENT,light0_color);
 124       glLightfv( GL_LIGHT1,GL_POSITION,light1_pos);
 125       glLightfv( GL_LIGHT1,GL_DIFFUSE,light1_color);
 126       glLightfv( GL_LIGHT1,GL_AMBIENT,light1_color);
 127       glEnable(GL_LIGHT0);
 128       glEnable(GL_LIGHT1);
 129
 130       glTranslatef(0,30+cos(lightangle/10.0)*cos(lightangle/5.0)*20.0,0);
 131       glRotatef(cos(lightangle)*5.0,0,2.0,0);
 132       glRotatef(cos(lightangle*2.0),0,0,2.0);
 133       glColor3f(1,1,0);
 134       gluQuadricTexture(quadric, GL_FALSE);         // halt  texture coordinate generation
 135       gluQuadricDrawStyle(quadric, GLU_FILL );
 136       gluQuadricDrawStyle(quadric, GLU_OUTSIDE );
 137       gluQuadricNormals(quadric, GL_SMOOTH);
 138       gluSphere        (quadric, 30.0f, 18, 18);    // radius, slices, stacks
 139       glRotatef(90,1,0,0);
 140       glColor3f(1,1,0);
 141       gluQuadricDrawStyle(quadric, GLU_LINE);
 142       gluCylinder(quadric,30,10,50,12,2);
 143       glTranslatef(0,0,50);
 144       gluQuadricDrawStyle(quadric, GLU_FILL);
 145       gluCylinder(quadric,10,8,10,12,12);
 146
 147       al_flip_display();
 148      }
 149   }
 150    close_and_exit();
 151}

Edgar Reynaldo

NSND! Let's see it!

MikiZX

Oh.. ok..
{"name":"612522","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/7\/3\/7383936d0090dfd1c00ea7c2d50fce70.png","w":606,"h":463,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/7\/3\/7383936d0090dfd1c00ea7c2d50fce70"}

Edgar Reynaldo

dang, that's pretty good. Now just smooth out the sides, and you're golden.

pmprog

@MikiZX: Out of curiousity, is there any reason you didn't use the Allegro 3D transform functions and primitive rendering?

MikiZX

Hm.. honestly said I was 'thinking in OpenGL' at the time and did not even think of Allegro5's transforms - I was just happy it worked.
Also, initialization of OpenGl and the part that sets the projection matrix come from posts posted on this forum few years ago by Edgar.
Though I am likely wrong, now that I think about it I think Allegro5 transforms are 2d oriented (Edgar is likely to correct or confirm this)? I think with Allegro5 transforms you always get a 2d/Ortho projection... ?

Edgar Reynaldo

There are 2D and 3D transformations. The 2D transformations use 3D under the hood.

The projection matrix is whatever you set it to. It's all 3D under the hood. Ortho just gives you a flat space in a certain plane to work with.

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