TriangleRotation.cpp

#include<stdio.h>
#include<graphics.h>
#include<math.h>

// pre-processor directories to calculate co-ordinates for the displaying device
#define fx(x) (getmaxx()/2+x)    
#define fy(y) (getmaxy()/2-y)

// pre-processor directory to calculate the round-off value to the nearest integer
#define R(x) ((int)(x+0.5))

// required constants
#define PI 3.14
#define X 640
#define Y 480
// colors
#define LWHITE 7
#define LCYAN 3
#define IMAGENTA 13
#define YELLOW 14

void drawQuadrants();   // function prototype to create quadrants
void drawTriangle(int,int,int,int,int,int,int); // function prototype to draw triangles 

int main(void)
/* (x1,y1), (x2,y2) and (x3,y3) are the co-ordinates of the vertices of a traingle. 
   'a' is the angle(in degree) through which the triangle is supposed to be rotated. 'r' is the radian couterpart of the same.
   All these are initialized from before in this piece of code. To avoid any loss of generality, take user-inputs.
   
   
   After rotaion through angle 'a' once w.r.t. the point (x1,y1), the new co-ordinates of the traingle are:
         (x1,y1),(nx2,ny2) and (nx3,ny3).

   After rotaion through angle 'a' twice w.r.t the point (x1,y1), the new co-ordinates of the traingle are:
         (x1,y1),(mx2,my2) and (mx3,my3).
         
   A pre-defined function 'initwindow()' has been used to create the displaying screen.
   
   A user-defined function 'drawQuadrants()' has been used to draw the co-ordinate axes.
   
   Another user-defined function 'drawTriangle()' has been used to draw a triangle.
   
*/
{
    int x1=10,y1=10,x2=x1+50,y2=y1-35,x3=x1-25,y3=y1-63,a=60,nx2,ny2,nx3,ny3,mx2,my2,mx3,my3;
    double r;        // declaring and initializing variables
    initwindow(X,Y);     // creating window
    drawQuadrants(); // calling function to draw quadrants
    //drawing the given triangle
    drawTriangle(x1,y1,x2,y2,x3,y3,LWHITE);
    
    r=a*(PI/180);    // converting the rotating angle to radian
    
    // rotating once w.r.t (x1,y1)
    // calcluating the new positions of the points (x2,y2) and (x3,y3)
    nx2=R(((x2*(cos(r)))-(y2*(sin(r)))));                   
    ny2=R(((x2*(sin(r)))+(y2*(cos(r)))));                   
    nx3=R(((x3*(cos(r)))-(y3*(sin(r)))));                   
    ny3=R(((x3*(sin(r)))+(y3*(cos(r)))));                   
    
    //drawing the rotated triangle
    drawTriangle(x1,y1,nx2,ny2,nx3,ny3,IMAGENTA);
    
    // rotating twice w.r.t (x1,y1)
    // calcluating the new positions of the points (nx2,ny2) and (nx3,ny3)
    mx2=R(((nx2*(cos(r)))-(ny2*(sin(r)))));                   
    my2=R(((nx2*(sin(r)))+(ny2*(cos(r)))));                   
    mx3=R(((nx3*(cos(r)))-(ny3*(sin(r)))));                   
    my3=R(((nx3*(sin(r)))+(ny3*(cos(r)))));                   
    
    //drawing the rotated triangle
    drawTriangle(x1,y1,mx2,my2,mx3,my3,YELLOW);
    
     
    getch();
    return 0;
}  // end of main

// function definition to create quadrants
void drawQuadrants()
{
    setcolor(LCYAN);   // setting a color for the co-ordinate axes
    line(0,fy(0),X,fy(0));   // drawing the X-axis; fy(0)=480/2=240;
    line(fx(0),0,fx(0),Y);   // drawing the Y-axis; fx(0)=640/2=320;
}

// function definition to create quadrants
void drawTriangle(int x1,int y1,int x2,int y2,int x3,int y3,int color)
{
     setcolor(color);    // setting a color for the triangle
     // drawing the respective lines
     line(fx(x1),fy(y1),fx(x2),fy(y2));
     line(fx(x2),fy(y2),fx(x3),fy(y3));
     line(fx(x3),fy(y3),fx(x1),fy(y1));
}