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

const int icaskrok = 25; // v milisekundach

const float Lmax = 20.0; // rozmer sceny v smere X

float surX = 0.0;  

void aktualizuj(const int ihod)
{
	surX += 0.05;
	glutPostRedisplay();
	glutTimerFunc(icaskrok, aktualizuj, ihod+1);
}

void obsluhaResize(int sirka, int vyska)
{
        glViewport(0, 0, sirka, vyska);
        glMatrixMode(GL_PROJECTION);  
	glLoadIdentity();
	if (sirka == 0) sirka++;
	const float pomstr = ((float)vyska)/sirka;
	gluOrtho2D(-0.5*Lmax, 0.5*Lmax, -0.5*Lmax*pomstr, 0.5*Lmax*pomstr);
}

void kresliTrojuh2D()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(0.0, 0.0, 1.0);
	
	glLoadIdentity();
	
	glTranslatef(surX, 0.0, 0.0);

	glBegin(GL_TRIANGLES);
		glVertex2f(-0.1*Lmax, -0.1*Lmax);
		glVertex2f( 0.1*Lmax, -0.1*Lmax);
		glVertex2f( 0.0*Lmax,  0.1*Lmax);

	glEnd();

	glutSwapBuffers();
}

int main(int argc, char **argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE);
	glutInitWindowSize(1080, 640);
	glutInitWindowPosition(200, 150);
	glutCreateWindow("OpenGL: trojuholnik");
	glutDisplayFunc(kresliTrojuh2D);
	glClearColor(0.8, 0.3, 0.3, 0.3);
	glutReshapeFunc(obsluhaResize);
	glutTimerFunc(icaskrok, aktualizuj, 0);
	glutMainLoop();
	return 0;
}