INT32GP Graphics Programming: Tutorial #06
Managing World Coordinates and Viewports, N-gons

1. Add a keyboard callback to the bottom of void setUpGLUT(int argc,char ** argv) .
   glutKeyboardFunc(keyboard);
2. Write the keyboard function and a function to reverse the coordinates(or copy and paste the code below).

   void reverse(int coordinate){
      /*
      ** Reverse the coordinates of the world window
      ** so that the image turns back to front or
      ** upside down. Note: x and y are enumerated
      ** data types declared globally.
      ** IN: value indicating whether to reverse the
      **     x or y coordinates.
      */
      GLdouble temp;
      if(coordinate==y){
         temp=yTop;
         yTop=yBottom;
         yBottom=temp;
      }
      else{
         temp=xLeft;
         xLeft=xRight;
         xRight=temp;
      }
   }
   void keyboard(unsigned char key,int xMouse,int yMouse){
      switch(key){
         case 27: exit(0);
         case 'u':reverse(y); break;
         case 'b':reverse(x); break;
      }
      glutPostRedisplay();
   }

3. Locate the following code in void reshape(int w,int h) and move it to the top of void display().

      /* Tell OpenGL to clear out whatever is in
      ** the PROJECTION matrix and (re)set
      ** the abstract world coordinates.
      */
      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();
      gluOrtho2D(xLeft,xRight,yBottom,yTop);
      /*
      ** It is a good programming habit to return the
      ** matrix mode to the default MODELVIEW matrix.
      */
      glMatrixMode(GL_MODELVIEW);
      glLoadIdentity();

1. Add a keyboard callback to the bottom of void setUpGLUT(int argc,char ** argv) .
   glutSpecialFunc(specialKeys);
2. Write the code for the specialKeys callback (or copy and paste the code below).

   void specialKeys(int key,int xMouse,int yMouse){
      switch(key){
         case GLUT_KEY_RIGHT: xLeft-=0.1; xRight-=0.1; break;
      }
      glutPostRedisplay();
   }

3. Observe how moving the x-coordinates left appears to cause the image to move right.
4. Add your own code to move the x-coordinates right (image left) in response to input from GLUT_KEY_LEFT.
5. Add similar code of your own to move the image up and down in response to GLUT_KEY_UP and GLUT_KEY_DOWN.

1. Replace void renderView() with three functions, one for each view. Use the code below if you like.

   void bottomView(){
      glViewport(xOrigin,yOrigin,width,height/3);
      glColor3dv(colour[red]);
      render(star,starSize,GL_LINE_LOOP);
   }
   void middleView(){
      glViewport(xOrigin,height/3,width,height/3);
      glColor3dv(colour[cyan]);
      render(star,starSize,GL_LINE_LOOP);
   }
   void topView(){
      glViewport(xOrigin,height/3*2,width,height/3);
      glColor3dv(colour[green]);
      render(star,starSize,GL_LINE_LOOP);
   }

2. Call each of these functions from void display(), after clearing the GL_COLOR_BUFFER_BIT and before glFlush();.
3. When you turn the the images upside down, do they respond as expected to the up and down arrow keys?

1. Set up vertex arrays for the triangle and circle using the algorithm and code discussed in tutorial #05.
2. Edit the void middleView()and void topView() functions, making appropriate changes to render the triangle and circle (as discussed in tutorial #05).

1. Create images using arcs of a circle based on the algorithm you developed for tutorial #05.