/*  checker.c
 *  This program texture maps a checkerboard image onto
 *  two rectangles.  This program clamps the texture, if
 *  the texture coordinates fall outside 0.0 and 1.0.
 */
#include <GL/glut.h>

/*	Create checkerboard texture	*/
#define	checkImageWidth 64
#define	checkImageHeight 64
GLubyte checkImage[checkImageWidth][checkImageHeight][3];

void makeCheckImage(void)
{
    int i, j, c;
    
    for (i = 0; i < checkImageWidth; i++) {
	for (j = 0; j < checkImageHeight; j++) {
	    c = ((((i&0x8)==0)^((j&0x8)==0)))*255;
	    checkImage[i][j][0] = (GLubyte) c;
	    checkImage[i][j][1] = (GLubyte) c;
	    checkImage[i][j][2] = (GLubyte) c;
	}
    }
}

void myinit(void)
{    
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);

    makeCheckImage();
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexImage2D(GL_TEXTURE_2D, 0, 3, checkImageWidth, 
	checkImageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, 
	&checkImage[0][0][0]);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    glEnable(GL_TEXTURE_2D);
    glShadeModel(GL_FLAT);
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBegin(GL_QUADS);
    glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
    glTexCoord2f(0.0, 1.0); glVertex3f(-2.0, 1.0, 0.0);
    glTexCoord2f(1.0, 1.0); glVertex3f(0.0, 1.0, 0.0);
    glTexCoord2f(1.0, 0.0); glVertex3f(0.0, -1.0, 0.0);

    glTexCoord2f(0.0, 0.0); glVertex3f(1.0, -1.0, 0.0);
    glTexCoord2f(0.0, 1.0); glVertex3f(1.0, 1.0, 0.0);
    glTexCoord2f(1.0, 1.0); glVertex3f(2.41421, 1.0, -1.41421);
    glTexCoord2f(1.0, 0.0); glVertex3f(2.41421, -1.0, -1.41421);
    glEnd();
    glutSwapBuffers();
}

void myReshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, 1.0*(GLfloat)w/(GLfloat)h, 1.0, 30.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.0, 0.0, -3.6);
}

void keyboard (unsigned char key, int x, int y)
{
   switch (key) {
      case 's':
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
         glutPostRedisplay();
         break;
      case 'S':
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
         glutPostRedisplay();
         break;
      case 't':
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
         glutPostRedisplay();
         break;
      case 'T':
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
         glutPostRedisplay();
         break;
      case 27:
         exit(0);
         break;
      default:
         break;
   }
}

int
main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutCreateWindow("checker");
    myinit();
    glutReshapeFunc (myReshape);
    glutDisplayFunc(display);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;             /* ANSI C requires main to return int. */
}