2D scaling Without Using OpenGL Function For Scaling

Program to draw a square of side 100 units at the center of the screen and scale it such that it enlarges to a square of side 150 units without using OpenGL function for scaling

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

int i;
float scalex, scaley, a[10], b[10], x, y, square_side;

void line(float x, float y, float a, float b)
{
  glBegin(GL_LINES);
  glVertex2f(x, y);
  glVertex2f(a, b);
  glEnd();
}

void display_square()
{
  for(i = 0; i < 4; i++)
  {
    if(i != 3)
      line(a[i], b[i], a[i+1], b[i+1]);
    else
      line(a[i], b[i], a[0], b[0]);
  }
}

void Init()
{
  /* Set clear color to white */
  glClearColor(1.0, 1.0, 1.0, 0);
  /* Set fill color to black */
  glColor3f(0.0, 0.0, 0.0);
  gluOrtho2D(0.0 , 640.0 , 0.0 , 480.0);
}

void scale()
{
  // Find the translated rectangle vertices
  for(i = 0; i < 4; i++)
  {
    a[i] = a[i] * scalex; b[i] = b[i] * scaley;
  }
}

void draw()
{
 glClear(GL_COLOR_BUFFER_BIT);

  // Find the original square vertices
  // (x, y) represents the upper left point
  x = 270.0; y = 290.0;

  a[0] = x; b[0] = y;
  a[1] = x + square_side; b[1] = y;
  a[2] = x + square_side; b[2] = y - square_side;
  a[3] = x; b[3] = y - square_side;
  // Draw original square
  display_square();

  // Perform scaling
  scale();
  // Draw scaled square using dotted lines
  glEnable(GL_LINE_STIPPLE);
  glLineStipple(1, 0xF0F0);
  display_square();
  glDisable(GL_LINE_STIPPLE);

  glFlush();
}

void main(int argc, char **argv)
{
  square_side = 100;
  printf("\n************************************************\n");
  printf("Length of the side of the square: %f\n", square_side);

  scalex = 1.5;
  scaley = 1.5;
  printf("\n************************************************\n");
  printf("Scaling factor along both directions: %f\n", scalex);
  printf("\n************************************************\n");

  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowPosition(0, 0);
  glutInitWindowSize(640, 480);
  glutCreateWindow("Scaling");
  Init();
  glutDisplayFunc(draw);
  glutMainLoop();
}

Written by Munia Balayil

2D Rotation Without Using OpenGL Function For Rotation

Program to perform 2D rotation without using OpenGL function for rotation

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

int x, y, p, q, xa, ya, ra, i, a[10], b[10], da, db;
float dx, dy, theta;

void line(int x, int y, int a, int b)
{
  glVertex2d(x, y);
  glVertex2d(a, b);
}

void display_rectangle()
{
  for(i = 0; i < 4; i++)
  {
    if(i != 3)
      line(a[i], b[i], a[i+1], b[i+1]);
    else
      line(a[i], b[i], a[0], b[0]);
  }
}

void Init()
{
  /* Set clear color to white */
  glClearColor(1.0, 1.0, 1.0, 0);
  /* Set fill color to black */
  glColor3f(0.0, 0.0, 0.0);
  gluOrtho2D(0 , 640 , 0 , 480);
}

void rotate()
{
  // Find the vertices of the rotated rectangle
  theta = (float)(ra*(3.14/180));
  for(i = 0;i<4;i++)
  {
    a[i] = (xa + ((a[i] - xa)*cos(theta) - (b[i] - ya)*sin(theta)));
    b[i] = (ya + ((a[i] - xa)*sin(theta) + (b[i] - ya)*cos(theta)));
  }
}

void transform()
{
  glClear(GL_COLOR_BUFFER_BIT);

  glBegin(GL_LINES);
  // Find the original rectangle vertices
  da = p - x; db = q - y;
  a[0] = x; b[0] = y;
  a[1] = x + da; b[1] = y;
  a[2] = x + da; b[2] = y + db;
  a[3] = x; b[3] = y + db;

  // Draw original rectangle
  display_rectangle();

  rotate();
  
  // Draw rotated rectangle
  display_rectangle();
  
  glEnd();

  glFlush();

}

void main(int argc, char **argv)
{
  printf("\n**********************************************\n");
  printf("Enter the upper left corner of the rectangle:\n");
  scanf("%d%d", &x, &y);
  printf("\n**********************************************\n");
  printf("Enter the lower right corner of the rectangle:\n");
  scanf("%d%d", &p, &q);

  printf("\n********************Rotation********************\n");
  printf("Enter the value of fixed point and angle of rotation:\n");
  scanf("%d%d%d", &xa, &ya, &ra);

  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowPosition(0, 0);
  glutInitWindowSize(640, 480);
  glutCreateWindow("Rotation");
  Init();
  glutDisplayFunc(transform);
  glutMainLoop();
}

Written by Munia Balayil