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

/* Minimum stack space */
static USED const char *stack = "$STACK:65535";

GLuint MakeTexture(void)
{
	int i, j;
	char *image = malloc(16*16);
	GLuint t;

	for (i = 0; i < 16; i++) {
		for (j = 0; j < 16; j++) {
			image[i*16+j] = i*j;
		}
	}
	glGenTextures(1, &t);
	glBindTexture(GL_TEXTURE_2D, t);
	glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

	// The filter settings were missing in this example.
	// However, MiniGL's results were as if those two lines here were present.
	// Which is actually a bug in MiniGL, because according to the OpenGL-specs,
	// the default values should be GL_NEAREST_MIPMAP_LINEAR (min) and GL_LINEAR (mag).
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);	
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

	glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, 16, 16, 0, GL_ALPHA,
		GL_UNSIGNED_BYTE, image);

	return t;
}


void display (void)
{
	glClearColor(0.2, 0.2, 0.2, 0.0);
	glClear (GL_COLOR_BUFFER_BIT);

	glColor4f(1.0, 1.0, 1.0, 1.0);

	glBegin (GL_QUADS);
		glTexCoord2f(0.0, 0.0);
		glVertex3f (-1.0, -1.0, 0.0);

		glTexCoord2f(1.0, 0.0);
		glVertex3f (1.0, -1.0, 0.0);

		glTexCoord2f(1.0, 1.0);
		glVertex3f (1.0, 1.0, 0.0);

		glTexCoord2f(1.0, 0.0);
		glVertex3f (-1.0, 1.0, 0.0);
	glEnd();
}

void myReshape(int w, int h)
{
	glViewport (0, 0, w, h);
	glMatrixMode (GL_PROJECTION);
	glLoadIdentity ();

	glOrtho (-1.5, 1.5, -1.5*(GLdouble)h/(GLdouble)w,
		1.5*(GLdouble)h/(GLdouble)w, -10.0, 10.0);
	glMatrixMode (GL_MODELVIEW);
}

static void
key(unsigned char k, int x, int y)
{
	switch (k) {
	case 27:  /* Escape */
		exit(0);
		break;

	case '1':
		glShadeModel(GL_SMOOTH);
		break;

	case '2':
		glShadeModel(GL_FLAT);
		break;
	}
	glutPostRedisplay();
}

/*  Main Loop
 *  Open window with initial window size, title bar,
 *  RGBA display mode, and handle input events.
 */
int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
	glutInitWindowSize (400, 400);
	glutCreateWindow (argv[0]);
	glutReshapeFunc (myReshape);
	glutDisplayFunc(display);
	glutKeyboardFunc(key);
	MakeTexture();
	glEnable(GL_BLEND);

	// The blend-func setting was missing in this example.
	// However, MiniGL's results were as if this line here was present.
	// Which is actually a bug in MiniGL, because according to the OpenGL-specs,
	// the default value should be (GL_ONE, GL_ZERO).
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

	glEnable(GL_TEXTURE_2D);
	glutMainLoop();
	return 0;             /* ANSI C requires main to return int. */
}