9 OpenGL Program for 2D Transformation 1) Translation 2) Scaling 3) Rotation on a Polygon ~ Coding Atharva

Program:

#include<GL/glut.h>
#include<math.h>

double parr[8];

void init()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glClearColor(0,0,0,1);
	glColor3f(1,0,1);
	gluOrtho2D(-500,500,-500,500); // Left,right,bottom,top
	
	// Polygon Defaut
	parr[0] = 10;  //x
	parr[1] = 10;  //y
	
	parr[2] = 200;
	parr[3] = 10;
	
	parr[4] = 200;
	parr[5] = 200;
	
	parr[6] = 10;
	parr[7] = 200;
}

double degreeToRad(double deg)
{
    return 3.14*(deg/180);	
}

void polygon()
{
	glColor3f(1,0,0);
	glBegin(GL_LINE_LOOP);
		glVertex2f(parr[0],parr[1]);
		glVertex2f(parr[2],parr[3]);
		
		glVertex2f(parr[4],parr[5]);
		glVertex2f(parr[6],parr[7]);
	glEnd();
	
	glFlush();
}


void drawCorodinates()
{
	glClear(GL_COLOR_BUFFER_BIT);

	glColor3f(1,1,1);
	glPointSize(4);
	
	glBegin(GL_LINES);
		glVertex2f(-500,0);
		glVertex2f(500,0);
		
		glVertex2f(0,500);
		glVertex2f(0,-500);
	glEnd();
	
	glColor3f(1,0,0);
	
	glBegin(GL_POINTS);
		glVertex2f(0,0);
	glEnd();
	
	glFlush();
}


// Translation
void translate2d()
{
   // 40px in x 
   // 50px in y
	
    int i = 0;
    int x = 40, y = 50;
    
    for(i= 0;i<7;i=i+2)
    {
    	parr[i] = parr[i] + x;
    }
    
    for(i = 1;i<7;i=i+2)
    {
    	parr[i] = parr[i] + y;
    }
    
    polygon();	
}


// Rotation
void rotation()
{
    double angle = 180,rad,x,y;
    rad = degreeToRad(angle);
    
    for(int i=0;i<8;i=i+2)
    {
	    x = parr[i]*cos(rad) - parr[i+1]*sin(rad);
	    y = parr[i]*sin(rad) + parr[i+1]*cos(rad);
    	    
    	    parr[i] = x;
    	    parr[i+1] = y;
    }    
    	
    polygon();	
}

// Scaling
void scaling2d()
{
   // 2 unit in x 
   // 2 unit in y
	
    int i = 0;
    double x = 0.5, y = 0.5;
    
    for(i= 0;i<7;i=i+2)
    {
    	parr[i] = parr[i] * x;
    	parr[i+1] = parr[i+1] * y;
    }
    
    
    polygon();	
}


void menu(int ch)
{
        drawCorodinates();
	switch(ch)
	{
		case 1: polygon();
			break;
		
		case 2: translate2d();
			break;
		case 3: scaling2d();
			break;
		case 4: rotation();
			break;	
	}
}


int main(int argc,char **argv)
{
	glutInit(&argc,argv);
	glutInitWindowSize(500,500);
	glutInitWindowPosition(100,100);
	
	glutCreateWindow("2D Transformation");
	init();
	glutDisplayFunc(drawCorodinates);
	
	glutCreateMenu(menu);
		glutAddMenuEntry("1 Display Polygon",1);
		glutAddMenuEntry("2 Translate",2);
		glutAddMenuEntry("3 Scaling",3);
		glutAddMenuEntry("4 Rotation",4);			
	glutAttachMenu(GLUT_RIGHT_BUTTON);
	
	glutMainLoop();	
	return 0;
}

Output:

1) Display Menu