/*  texgen.c
 *  This program draws a texture mapped teapot with 
 *  automatically generated texture coordinates.  The
 *  texture is rendered as stripes on the teapot.
 *  Initially, the object is drawn with texture coordinates
 *  based upon the object coordinates of the vertex
 *  and distance from the plane x = 0.  Pressing the 'e'
 *  key changes the coordinate generation to eye coordinates
 *  of the vertex.  Pressing the 'o' key switches it back
 *  to the object coordinates.  Pressing the 's' key 
 *  changes the plane to a slanted one (x + y + z = 0).
 *  Pressing the 'x' key switches it back to x = 0.
 */

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

#define	stripeImageWidth 32
GLubyte stripeImage[4*stripeImageWidth];

#ifdef GL_VERSION_1_1
static GLuint texName;
#endif

void makeStripeImage(void)
{
   int j;
    
   for (j = 0; j < stripeImageWidth; j++) {
      stripeImage[4*j] = (GLubyte) ((j<=4) ? 255 : 0);
      stripeImage[4*j+1] = (GLubyte) ((j>4) ? 255 : 0);
      stripeImage[4*j+2] = (GLubyte) 0;
      stripeImage[4*j+3] = (GLubyte) 255;
   }
}

/*  planes for texture coordinate generation  */
static GLfloat xequalzero[] = {1.0, 0.0, 0.0, 0.0};
static GLfloat slanted[] = {1.0, 1.0, 1.0, 0.0};
static GLfloat *currentCoeff;
static GLenum currentPlane;
static GLint currentGenMode;

void init(void)
{
   glClearColor (0.0, 0.0, 0.0, 0.0);
   glEnable(GL_DEPTH_TEST);
   glShadeModel(GL_SMOOTH);

   makeStripeImage();
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1); // <--- stripImage: 4bytes

#ifdef GL_VERSION_1_1
   glGenTextures(1, &texName);
   glBindTexture(GL_TEXTURE_1D, texName); // <---
#endif
   glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_REPEAT);
   glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
   glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
#ifdef GL_VERSION_1_1
   glTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA, stripeImageWidth, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, stripeImage);
#else
   glTexImage1D(GL_TEXTURE_1D, 0, 4, stripeImageWidth, 0,
                GL_RGBA, GL_UNSIGNED_BYTE, stripeImage);
#endif

   glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
   currentCoeff = xequalzero;
   currentGenMode = GL_OBJECT_LINEAR;
   currentPlane = GL_OBJECT_PLANE;
   glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, currentGenMode);
   glTexGenfv(GL_S, currentPlane, currentCoeff);

   glEnable(GL_TEXTURE_GEN_S);
   glEnable(GL_TEXTURE_1D);
   glEnable(GL_CULL_FACE);
   glEnable(GL_LIGHTING);
   glEnable(GL_LIGHT0);
   glEnable(GL_AUTO_NORMAL);
   glEnable(GL_NORMALIZE);
   glFrontFace(GL_CW);
   glCullFace(GL_BACK);
   glMaterialf (GL_FRONT, GL_SHININESS, 64.0);
}

void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

   glPushMatrix ();
   glRotatef(45.0, 0.0, 0.0, 1.0);
#ifdef GL_VERSION_1_1
   glBindTexture(GL_TEXTURE_1D, texName);
#endif
   glutSolidTeapot(2.0);
   glPopMatrix ();
   glFlush();
}

void reshape(int w, int h)
{
   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (w <= h)
      glOrtho (-3.5, 3.5, -3.5*(GLfloat)h/(GLfloat)w, 
               3.5*(GLfloat)h/(GLfloat)w, -3.5, 3.5);
   else
      glOrtho (-3.5*(GLfloat)w/(GLfloat)h, 
               3.5*(GLfloat)w/(GLfloat)h, -3.5, 3.5, -3.5, 3.5);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

void keyboard (unsigned char key, int x, int y)
{
   switch (key) {
      case 'e':
      case 'E':
         currentGenMode = GL_EYE_LINEAR;
         currentPlane = GL_EYE_PLANE;
         glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, currentGenMode);
         glTexGenfv(GL_S, currentPlane, currentCoeff);
         glutPostRedisplay();
         break;
      case 'o':
      case 'O':
         currentGenMode = GL_OBJECT_LINEAR;
         currentPlane = GL_OBJECT_PLANE;
         glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, currentGenMode);
         glTexGenfv(GL_S, currentPlane, currentCoeff);
         glutPostRedisplay();
         break;
      case 's':
      case 'S':
         currentCoeff = slanted;
         glTexGenfv(GL_S, currentPlane, currentCoeff);
         glutPostRedisplay();
         break;
      case 'x':
      case 'X':
         currentCoeff = xequalzero;
         glTexGenfv(GL_S, currentPlane, currentCoeff);
         glutPostRedisplay();
         break;
      case 27:
         exit(0);
         break;
      default:
         break;
   }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
   glutInitWindowSize(256, 256);
   glutInitWindowPosition(100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display);
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;
}