// Viewport --- Demonstration of using OpenGL viewports and
//    rendering text.
//
// Tom Kelliher, Feb. 5, 2001.


#define ESC 0x1b


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


void display(void);
void reshape(int w, int h);
void idle(void);
void mouse(int btn, int action, int x, int y);
void keyboard(unsigned char key, int x, int y);


int gww = 200;    // Window width.
int gwh = 200;    // Window height.
int redraw = 1;      // Flag for idle func.
GLuint list;      // Display list for polygons.
int maintainAspectRatio = 0;
int realtimeRedraw = 1;

int main(int argc, char **argv)
{

   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
   glutInitWindowPosition(100, 100);
   glutInitWindowSize(gww, gwh);
   glutCreateWindow("Viewport Experiment");

   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(0.0, 10.0, 0.0, 10.0, -1.0, 1.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();

   list = glGenLists(1);         // Get display list ID.
   glNewList(list, GL_COMPILE);  // Create display list.
      glBegin(GL_POLYGON);
         glVertex2d(0.0, 0.0);
         glVertex2d(0.0, 5.0);
         glVertex2d(2.0, 5.0);
         glVertex2d(2.0, 0.0);
      glEnd();
      glBegin(GL_POLYGON);
         glVertex2d(8.0, 8.0);
         glVertex2d(8.0, 10.0);
         glVertex2d(10.0, 10.0);
         glVertex2d(10.0, 8.0);
      glEnd();
   glEndList();

   glutDisplayFunc(display);
   glutReshapeFunc(reshape);
   glutIdleFunc(idle);
   glutMouseFunc(mouse);
   glutKeyboardFunc(keyboard);

   glutMainLoop();

   return 0;
}


// display --- Generate the polygons using different
//    viewports.  Note the distortion when the aspect ratios
//    between the clipping rectangle and the viewport differ.

void display(void)
{
   glClearColor(0.0, 0.0, 0.0, 0.0);
   glClear(GL_COLOR_BUFFER_BIT);

   glColor3d(1.0, 1.0, 1.0);
   glViewport(0, 0, gww, gwh);
   glCallList(list);

   glColor3d(1.0, 0.0, 0.0);
   glViewport(0, 0, gww / 2, gwh / 2);
   glCallList(list);

   glColor3d(0.0, 1.0, 0.0);
   glViewport(gww / 2, gwh / 2, gww / 2, gwh / 2);
   glCallList(list);

   glColor3d(0.0, 0.0, 1.0);
   glViewport(0, gwh / 2, gww / 4, gwh / 2);
   glCallList(list);

   glColor3d(1.0, 1.0, 0.0);
   glViewport(gww / 2, 0, gww / 2, gwh / 4);
   glCallList(list);

   glFlush();
   redraw = 1;    // Tell idle to redraw the text.
}


// reshape --- Record the new window size and call display.

void reshape(int w, int h)
{
   if (maintainAspectRatio)
      gww = gwh = (w < h) ? w : h;
   else
   {
      gww = w;
      gwh = h;
   }

   if (realtimeRedraw)
      display();
   else
      glutPostRedisplay();
}


// idle --- Just a stupid demonstration showing how to draw
//    text.

void idle(void)
{
   static int count = 0;

   if (!redraw)
      return;

   printf("Redrawing text: %d.\n", ++count);
   redraw = 0;

   glColor3d(1.0, 1.0, 1.0);
   glViewport(0, 0, gww, gwh);

   glRasterPos2d(7.5, 5);     // World coordinates.

   glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, 'T');
   glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, 'o');
   glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, 'm');

   glFlush();
}


void mouse(int btn, int action, int x, int y)
{
   if (btn == GLUT_LEFT_BUTTON && action == GLUT_DOWN)
      maintainAspectRatio = (maintainAspectRatio + 1) % 2;

   if (btn == GLUT_RIGHT_BUTTON && action == GLUT_DOWN)
      realtimeRedraw = (realtimeRedraw + 1) % 2;
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key)
   {
      case ESC:
         exit(0);
         break;
   }
}