/* Demo of the classic barn object.

Implemented Fall 2003
Scott D. Anderson
*/

#include <stdio.h>
#include <math.h> // for sqrt
#ifdef MAC
#include <GLUT/glut.h>
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>
#else
#include <GL/glut.h>
#endif

const int barnWidth =30;
const int barnHeight=40;
const int barnLength=50;

GLfloat barn[10][3] = 
{
  {0,0,0},                                 //left, bottom, front 
  {barnWidth,0,0},                         // right, bottom, front 
  {barnWidth,barnHeight,0},                 // right, top, front 
  {0,barnHeight,0},                         // left, top, front 
  {barnWidth/2.0,barnHeight+barnWidth/2.0,0}, // ridge, front 
  {0,0,-barnLength},                     // left, bottom, back 
  {barnWidth,0,-barnLength},             // right, bottom, back 
  {barnWidth,barnHeight,-barnLength},    //right, top, back 
  {0,barnHeight,-barnLength},            // left, top, back 
  {barnWidth/2.0,barnHeight+barnWidth/2.0,-barnLength},// ridge, back 
};

// Almost every facet is a different color so that we can see them.

void drawBarn() {
    int i;
    glColor3f(1,0,0);		// set color to red
    glBegin(GL_POLYGON);        // front 
    {
        glVertex3fv(barn[0]);
        glVertex3fv(barn[1]);
        glVertex3fv(barn[2]);
        glVertex3fv(barn[3]);
    }
    glEnd();
    glBegin(GL_POLYGON);        // front ridge 
    {
        glVertex3fv(barn[3]);
        glVertex3fv(barn[2]);
        glVertex3fv(barn[4]);
    }
    glEnd();
    glColor3f(0,1,0);
    glBegin(GL_POLYGON);        // back 
    {
        glVertex3fv(barn[5]);
        glVertex3fv(barn[6]);
        glVertex3fv(barn[7]);
        glVertex3fv(barn[8]);
    }
    glEnd();
    glBegin(GL_POLYGON);         // back ridge 
    {
        glVertex3fv(barn[7]);
        glVertex3fv(barn[8]);
        glVertex3fv(barn[9]);
    }
    glEnd();
    glColor3f(0.5,0,0.5);
    glBegin(GL_POLYGON);        // left side 
    {
      glVertex3fv(barn[0]);
      glVertex3fv(barn[3]);
      glVertex3fv(barn[8]);
      glVertex3fv(barn[5]);
    }
    glEnd();
    glColor3f(0.5,0,0);
    glBegin(GL_POLYGON);        // right side 
    {
      glVertex3fv(barn[1]);
      glVertex3fv(barn[2]);
      glVertex3fv(barn[7]);
      glVertex3fv(barn[6]);
    }
    glEnd();
    glColor3f(0.5,0.5,0);
    glBegin(GL_POLYGON);        // left side roof 
    {
      glVertex3fv(barn[3]);
      glVertex3fv(barn[4]);
      glVertex3fv(barn[9]);
      glVertex3fv(barn[8]);
    }
    glEnd();
    glBegin(GL_POLYGON);        /* right side roof */
    {
      glVertex3fv(barn[2]);
      glVertex3fv(barn[4]);
      glVertex3fv(barn[9]);
      glVertex3fv(barn[7]);
    }
    glEnd();
}

void init() {
  glDisable(GL_LIGHTING);
  glShadeModel(GL_FLAT);
  // Use a simple non-distorting (letterbox) perspective camera with
  // 90 degree fovy on a 4:3 shaped window, so the frustum is based on
  // the horizontal, which makes things just a little more complex.
  // Since we can't move the camera around without using TW, we'll
  // place the camera above and to the right of the barn, so you can
  // see the front, right side, and the roof.
  GLfloat BBheight = barnHeight+barnWidth/2.0;
  GLfloat BBdepth = barnLength;
  GLfloat BBwidth = barnWidth;
  GLfloat BBradius = 0.5*sqrt(BBheight*BBheight+BBdepth*BBdepth+BBwidth*BBwidth);
  GLfloat EyeRadius = BBradius*sqrt(2);
  // Compute Center of BB
  GLfloat CenterX = BBwidth/2;
  GLfloat CenterY = BBheight/2;
  GLfloat CenterZ = -BBdepth/2;
  // Place Eye equally far from Center along each axis
  GLfloat EyeOrthoDist = EyeRadius/sqrt(3);
  GLfloat EyeX = CenterX+EyeOrthoDist;
  GLfloat EyeY = CenterY+EyeOrthoDist;
  GLfloat EyeZ = CenterZ+EyeOrthoDist;
  EyeX = CenterX;
  EyeY = CenterY;
  EyeZ = CenterZ+EyeRadius;
  GLfloat fovy = 90;
  GLfloat aspectRatio = 4.0/3.0;
  GLfloat near = EyeRadius - BBradius;
  GLfloat far  = EyeRadius + BBradius;

  // Some debugging print statements:
  printf("BBradius = %f, EyeRadius =%f\n",BBradius,EyeRadius);
  printf("Center = (%f,%f,%f)\n",CenterX,CenterY,CenterZ);
  printf("aspect ratio = %f\nEyeRadius = %f, near=%f far=%f\nVRP=(%f,%f,%f)\n",
	 aspectRatio,EyeRadius,near,far,EyeX,EyeY,EyeZ);
  printf("EyeOrthoDist = %f\n",EyeOrthoDist);

  // Okay, finally ready for the OpenGL calls
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective(fovy,aspectRatio,near,far);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  gluLookAt(EyeX,EyeY,EyeZ,
	    CenterX,CenterY,CenterZ,
	    0,1,0);
}

void display(void) {
  glClearColor(0.75,0.75,0.75,1);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  drawBarn();

  glFlush();
  glutSwapBuffers();
}

int main(int argc, char** argv) {
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
  glutInitWindowSize(400,300);
  glutCreateWindow(argv[0]);
  glutDisplayFunc(display);
  glEnable(GL_DEPTH_TEST);
  init();
  glutMainLoop();
  return 0;
}