CG Event Handling Forum.......

Hi All,

PFA the code that demonstrates event handling mechanism in OpenGL.

Analyze the attached program thoroughly and get the answers for the below questions:

• When the program is run, initially why a window with white background is displayed?

• When middle button of the mouse is clicked, why nothing is drawn on the window?

• When left and right buttons are clicked, why circle and Sierpinski Gasket are drawn at different positions on the window?

• Is it possible to modify the code such that both circle and Sierpinski Gasket are drawn from the point where the mouse is clicked on the window?

• When window is maximized, why nothing is drawn on the window?

• What modifications in the code has to be made if the aspect ratio of the object drawn should remain the same when the window is resized/maximized?

• What modifications in the code has to be made so that the program should be terminated if the middle button of the mouse or 'q' / 'Q' key is pressed from the keyboard?

Thanks,

Govind N. & Vishal K


HAVE YOUR SAY IN THIS DISCUSSION FORUM......


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

void gasket();

void myinit()
{
      glClearColor(1.0, 1.0, 1.0, 1.0); /* white background */
      glColor3f(1.0, 0.0, 0.0); /* draw in red */
      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();
      gluOrtho2D(-10.0, 10.0, -10.0, 10.0);
      glMatrixMode(GL_MODELVIEW);
}
    
void draw()
{
    int r=10;
    GLfloat theta;
  
    glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_POLYGON);
for(theta=0; theta<=360; theta+=0.01)
     {
      glVertex2f(5*sin(theta*3.142/180), 5*cos(theta*3.142/180));
     }
glEnd();
     glFlush();
 }


void myMouse(int button, int state, int x,int y)
{
     if(button==GLUT_LEFT_BUTTON && state==GLUT_DOWN)
     {
      draw();
     }
     else if(button==GLUT_RIGHT_BUTTON && state==GLUT_DOWN)
     {
      gasket();
     }
}

void gasket()
{
     GLfloat v[3][2] = {{1.0, 1.0}, {6.0, 1.0}, {3.5, 5.5}};    // Assign co-ordinates to draw 3 points for triangle
     GLfloat p[2] = {2.5, 2.5};                                 // Take an initial point
     int j, i;
    
     glClear(GL_COLOR_BUFFER_BIT);
     glBegin(GL_POINTS);
     for(i=0; i<50000; i++)
     {
              j=rand()%3;                                       // Select a vertex randomly in each iteration
              p[0]=(p[0] + v[j][0])/2.0;                        // Compute the mid-point between P and selected vertex
              p[1]=(p[1] + v[j][1])/2.0;                        // Compute the mid-point between P and selected vertex
            
              glVertex2fv(p);                                   // Display this point on the screen
     }
     glEnd();
     glFlush();
}

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glFlush();
}

void myKey(unsigned char key, int x1, int y1)
{
     if(key=='c' || key=='C')
     {
      draw();
     }
     else if(key=='g' || key=='G')
     {
      gasket();
     }          
}

int main(int argc, char** argv)
{
    glutInit(&argc,argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); /* default, not needed */
    glutInitWindowSize(500,500); /* 500 x 500 pixel window */
    glutInitWindowPosition(0,0); /* place window top left on display */
    glutCreateWindow("Mouse and Key");
    glutDisplayFunc(display);
    glutMouseFunc(myMouse);  /* display callback invoked when window opened */
    glutKeyboardFunc(myKey);
    myinit(); /* set attributes */
    glutMainLoop(); /* enter event loop */
    return 0;
}