/* Contrast of perspective as a function of FOVY. 

Implemented Fall 2003
Scott D. Anderson
*/

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

#define GAP  25      /* gap between subwindows */
int leftWinWidth=400;
int leftWinHeight=400;
int rightWinWidth=400;
int rightWinHeight=400;

void parentDisplay(void) {
    twDisplayInit();
    glFlush();
    glutSwapBuffers();
}

GLfloat aspectRatio(int w, int h) {
    return ((GLfloat) w) / ((GLfloat) h);
}

void leftDisplay(void) {
    twDisplayInit(0.8,0.8,1.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(90,aspectRatio(leftWinWidth,leftWinHeight),1,3);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0,0,2, 0,0,0, 0,1,0);

    twColorName(TW_YELLOW);
    glutWireCube(1);
  
    glFlush();
    glutSwapBuffers();
}

void rightDisplay(void) {
    twDisplayInit(0.8,1.0,0.8);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    const GLfloat M = 10;	// multiplication factor
    // The following code calculates a fovy such that the focal point is M
    // times farther from the image plane than in the rightDisplay.  The
    // calculation is based on right triangle with legs of length 1 and M,
    // the fovy is double that angle, converted to degrees.
    GLfloat fovy = 2*atan(1/M)*180/M_PI;
    printf("fovy = %f degrees\n",fovy);
    gluPerspective(fovy,aspectRatio(rightWinWidth,rightWinHeight),M,2+M);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0,0,1+M, 0,0,0, 0,1,0);

    twColorName(TW_MAGENTA);
    glutWireCube(1);
  
    glFlush();
    glutSwapBuffers();
}

int parentWin, leftWin, rightWin;

void redisplayAll(void) {
    glutSetWindow(leftWin);
    glutPostRedisplay();
    glutSetWindow(rightWin);
    glutPostRedisplay();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
    glutInitWindowSize(leftWinWidth+rightWinWidth+GAP*3, 
		       leftWinHeight+GAP*2); //parent window
    parentWin = glutCreateWindow(argv[0]);
    glutDisplayFunc(parentDisplay);
    twBoundingBox(-1,1,-1,1,-1,1); // keeps twMainInit quiet
    twMainInit();

    /*glutCreateSubWindow returns the ID of the sub-window and takes 
      arguments:(int parent,int x,int y,int width,int height).
      Origin at x,y; height equals distance from y _down_ */
    leftWin = glutCreateSubWindow(parentWin,GAP,GAP,leftWinWidth,leftWinHeight);

    /*Each time you create a new window you need to give it its own 
      callbacks and initialization. These can be the same as those
      from other windows but you must call them each time*/
    twBoundingBox(-10,10,-10,10,-10,10);
    glutDisplayFunc(leftDisplay);
    twMainInit(); 

    rightWin = glutCreateSubWindow(parentWin,GAP*2+leftWinWidth,GAP,rightWinWidth,rightWinHeight);
    glutDisplayFunc(rightDisplay);
    twMainInit();
    glLineWidth(2);
  
    redisplayAll(); 
    glutMainLoop();
    return 0;
}