Use glScalef function

glScalef function:

                                        glScalef() function is use for scaling in OpenGL so the question is what is scaling?

scaling:

Scaling is about the origin. If Sx = Sy the scaling is uniform; otherwise it distorts the image. If Sx or Sy < 0, the image is reflected across the x or y axis. in scaling we multiply the object position with the scaling factor.so if object position is p(x,y) and scaling factor is s(x,y) so we can say that
                                                                  P'=p(x,y).s(x,y)
In two dimension scaling :

•(sx and sy )> 1 ---> Increases Object Size

•(sx and sy )< 1 ---> Decreases Object Size

•(sx and sy )= 1 ---> Unchanged Object Size

•sx = sy              ---> Uniform Scaling

•sx != sy             ---> Differential Scaling

types of scaling:

uniform scaling:                      

                                  if scaling factor are same then scaling is called is called uniform scaling

                                                                              Sx=Sy

Differential scaling:

                               if the scaling factor is not same then scaling is called differential scaling

                                                           Sx is not equal to Sy

scaling in openGl:

                                          glScalef() function is use for scaling in OpenGL

syntax:

                                glsaclef(x   , y  , z);

Example:

void Draw_scalling() {

glPushMatrix(); 

glScalef(0.2,0.2,0.0);

glBegin(GL_QUADS);        

    glColor3f(0.0f,1.0f,0.0f);    

    glVertex2f( 0.2, 0.49);    

    glVertex2f(0.4, 0.49);   

    glVertex2f(0.4, 0.76);    

    glVertex2f( 0.2, 0.76);    

       

glEnd();

glPopMatrix();

glFlush();

}

screen short:

Before scaling

After scaling

you can see the scaling effect in above fig after scaling you can see that your body is moved in left corner . so i am telling you before scaling is always about the origin so if u want that your image is not move toward the origin so you can use the gltranslatef() function here