3D Projection - Display of 3D object such as Cube using General Parallel Projection
#include<stdio.h>
#include<graphics.h>
#include<math.h>

void input(int x[],int y[],int z[],int no)
{
 int i;
 printf("Enter the co-ordinates\n");
 for(i=0;i<no;i++)
 {
  printf("P[%d]\t X%d:\t",i+1,i+1);
  scanf("%d",&x[i]);
  printf("P[%d]\t Y%d:\t",i+1,i+1);
  scanf("%d",&y[i]);
  printf("P[%d]\t Z%d:\t",i+1,i+1);
  scanf("%d",&z[i]);
 }
}


void printFigure_ortho(int x[],int y[],int z[],int no)
{
 int i;
 if(no==1)
 {
  putpixel(x[0],y[0],YELLOW);
 }
 else
 {
  for(i=0;i<no-1;++i)
  {
     line(x[i],y[i],x[i+1],y[i+1]);
  }

 }
 if(no>2)
 {
  line(x[0],y[0],x[no-1],y[no-1]);
 }
}


void getOblique(int x[],int y[],int z[],int no,float angle1,int xp[],int yp[],int choice)
{
 int i;
 for(i=0;i<no;++i)
 {
  if(choice==1)
  {
   xp[i]=x[i]+z[i]/tan(45)*cos(angle1);
   yp[i]=y[i]+z[i]/tan(45)*sin(angle1);
  }
  if(choice==2)
  {
   xp[i]=x[i]+z[i]/tan(63.4)*cos(angle1);
   yp[i]=y[i]+z[i]/tan(63.4)*sin(angle1);
  }
 }
}

void printFigure(int xp[],int yp[],int no)
{
 int i;
 if(no==1)
 {
  putpixel(xp[0],yp[0],YELLOW);
 }
 else
 {
  for(i=0;i<no-1;++i)
  {
     line(xp[i],yp[i],xp[i+1],yp[i+1]);
  }

 }
 if(no>2)
 {
  line(xp[0],yp[0],xp[no-1],yp[no-1]);
 }
}

int main()
{
 int gd=DETECT,gm;
 int x[10],y[10],z[10],no,xp[10],yp[10],choice;
 float angle1;
 clrscr();
 printf("Enter your choice:\n");
 printf("1.Point\n2.Line\n3.Triangle\n4.Square\n");
 printf("Or enter no of vertices for any polygon:\n");
 scanf("%d",&no);
 printf("Enter the angle PHI:\t");
 scanf("%f",&angle1);

 input(x,y,z,no);

 initgraph(&gd,&gm,"c:\\tc\\bgi");
 printf("\nOrthographics Projectio(WHITE):");

 printFigure_ortho(x,y,z,no);

 printf("Oblique Projection(YELLOW).Enter your choice:");
 printf("\n1.Cavalier Projection\t2.Cabinet Projection");
 scanf("%d",&choice);

 getOblique(x,y,z,no,angle1,xp,yp,choice);

 setcolor(YELLOW);
 printFigure(xp,yp,no);

 getch();
 return 0;
}