From:	"Anders Pedersen" <anders_p AT forum DOT dk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Allegro program won't work
Lines:	100
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Date:	Sat, 10 Apr 1999 12:35:10 +0200
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Organization:	get2net Internet Kunde
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

I'm trying to learn how to make 3d games. I've found an tutorial on the net
and readed it. After that I wanted to do some research, and I've done this
program that make an 3d rectangle (allmost there some lines in the rectangle
missing) that you can move around with the keypads an zoom in and out with Z
and X. The program work fine but when you try to zoom in so you can't se the
rectangle more the program crashes.

Anders

Program:
#include <allegro.h>

float x[4]={2,2,-2,-2}; // Here are the X and Y values
float y[4]={2,-2,2,-2}; // for the rectangle

float z=10; // And here are the z value

int screenx1,screeny1,screenx2,screeny2; // Some integers to store the
calculated points before they're blitted to the screen

int i; // Just an integer for the loop

int done=FALSE;

BITMAP *temp; // A doublebuffer

int main(void)
{
 allegro_init();

 set_gfx_mode(GFX_AUTODETECT,320,200,0,0);

 install_keyboard();

 temp=create_bitmap(320,200);


 do
 {
  for (i=0; i!=4; i++) // we need to draw 4 lines
  {

   screenx1=160.0+256.0*( x[i] / z);           // This algorithm
   screeny1=100.0+256.0*( y[i] / z);           // calculate where
   screenx2=160.0+256.0*( x[i] / (z+5.0)); // I should draw
   screeny2=100.0+256.0*( y[i] / (z+5.0)); // the line

   line(temp, screenx1, screeny1, screenx2, screeny2, 6); // draw the line
to the double buffer
  }
  blit(temp,screen,0,0,0,0,320,200);
  clear(temp);

  // getinput from keyboard
  if (key[KEY_UP])
  {
   y[0]--;   // Move rectangle up
   y[1]--;
   y[2]--;
   y[3]--;
  }
  if (key[KEY_DOWN])
  {
   y[0]++;   // Move rectangle down
   y[1]++;
   y[2]++;
   y[3]++;
  }
  if (key[KEY_LEFT])
  {
   x[0]--;   // move rectangle left
   x[1]--;
   x[2]--;
   x[3]--;
  }
  if (key[KEY_RIGHT])
  {
   x[0]++;    // move rectangle right
   x[1]++;
   x[2]++;
   x[3]++;
  }
  if (key[KEY_X])
  {
   z++;                  // Zoom in
  }
  if (key[KEY_Z])
  {
   z--;                  // Zoom out
  }
  if (key[KEY_ESC])
  {
   done=TRUE;               // exit program
  }
  clear_keybuf();
 } while (done==FALSE);
 return 0;
}

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