#include <stdio.h>
#include <stdlib.h>

#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

static void draw_it(int col)
{
	GLint view[4];
	int x0, y0, x1, y1;

	glGetIntegerv(GL_VIEWPORT, view);

	glColor3ub(col & 1 ? 255 : 0, col & 2 ? 255 : 0, col & 4 ? 255 : 0);

	x0 = (3 * view[0] + 1 * view[2]) / 4;
	y0 = (3 * view[1] + 1 * view[3]) / 4;
	x1 = (1 * view[0] + 3 * view[2]) / 4;
	y1 = (1 * view[1] + 3 * view[3]) / 4;

	glRecti(x0, y0, x1, y1);
}

static void display(void)
{
	glDrawBuffer(GL_BACK);
	glClear(GL_COLOR_BUFFER_BIT);
	draw_it(1);

	glutSwapBuffers();
}

void keyboard(unsigned char key, int x, int y)
{
	switch (key)
	{
	case '\e':
		exit(0);
		break;
	case 'r':
		glutPostRedisplay();
		break;
	case 'b':
		glDrawBuffer(GL_BACK);
		draw_it(2);
		break;
	case 'f':
		glDrawBuffer(GL_FRONT);
		draw_it(3);
		break;
	case 's':
		glutSwapBuffers();
		break;
	}
}

static void reshape(int w, int h)
{
	glViewport(0, 0, w, h);
	glPushAttrib(GL_TRANSFORM_BIT);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0, w, 0, h);
	glPopAttrib();
	glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char **argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
	glutInitWindowSize(640, 480);
	glutCreateWindow("Test");

	glutReshapeFunc(reshape);
	glutDisplayFunc(display);
	glutKeyboardFunc(keyboard);

	glutMainLoop();

	return 0;
}