/* Place a single pixel on the screen, and allow the user to move it around
in 3D with the cursor keys and PgUp/PgDn. A simple demonstration of how to
move points in 3D and reflect their position on a 2D computer screen. */

#include <graphics.h>
#include <bios.h>
#include <stdio.h>
#include <conio.h>

/* The 4 lines below set the screen_center variables */
int x_resolution = 640;
int y_resolution = 480;
int screen_center_x = x_resolution/2;
int screen_center_y = y_resolution/2;
/* --------------------- */

/* The vertex is the point in 3D. X, Y, and Z are its 3D coordinates */
double vertex_x = - 100, vertex_y = -100, vertex_z = 300;

/* screen_x and screen_y will be the actual final pixel coordinates */
int screen_x, screen_y;

/* "distance" is a theoretical variable indicating how far you, the viewer,
are from the screen */
int distance = 256;

/* keystroke will be used to read input from the keyboard */
int keystroke;

void PrintNewCoords() {
/* Print the new vertex's coordinates in
the upper-left corner of the screen */

cleardevice();
/* cleardevice clears the previous pixel instance. Comment out the above line
if you want to leave a trail instead of only having one pixel on-screen at a
time. */
gotoxy(1,1); /* Move text cursor to upper-left corner of screen */
printf("X = %f\n", vertex_x);
printf("Y = %f\n", vertex_y);
printf("Z = %f", vertex_z);

}

void DrawNewPoint() {
/* Draw the new pixel on the screen */

/* The two lines below are where all the real 3D work is done. These two
lines convert the 3D coordinates of the vertex into 2D coordinates for a
pixel on the screen. Once you know the algorithm, it's really that easy. */

screen_x = screen_center_x + distance * (vertex_x / vertex_z);
screen_y = screen_center_y - distance * (vertex_y / vertex_z);

/* And now, we just draw the pixel... */
putpixel (screen_x, screen_y, 9);

}

void GetKeyStroke() {

/* Get a keystroke */
keystroke = _bios_keybrd(_NKEYBRD_READ);
switch (keystroke) {
  case 19424: /* left arrow */
	      vertex_x = vertex_x - 1;
	      break;
  case 19936: /* right arrow */
	      vertex_x = vertex_x + 1;
	      break;
  case 20704: /* down arrow */
	      vertex_y = vertex_y - 1;
	      break;
  case 18656: /* up arrow */
	      vertex_y = vertex_y + 1;
	      break;
  case 18912: /* PgUp */
	      vertex_z = vertex_z + 1;
	      break;
  case 20960: /* PgDn */
	      vertex_z = vertex_z - 1;
	      break;

}
}

main()

{

/* The two lines below just initialize the graphics mode. */
int gdriver=VGA, gmode=2;
initgraph(&gdriver, &gmode, "C:\\TC\\BGI");

/* Quit if the user presses q. Otherwise, let the user use the cursor keys
(to control 2D motion) and PgUp and PgDn (to control depth), and adjust the
point on-screen accordingly. */

while (keystroke != 4209) {
PrintNewCoords();
DrawNewPoint();
GetKeyStroke();
}

return(0);

}