#include <GL/glut.h>

static GLfloat Rotationswinkel = 0.0;
static GLuint Animationsverzögerung = 10;

void reshape(GLint w, GLint h) {
    glViewport(0, 0, w, h);
    GLfloat aspect = (GLfloat)w / (GLfloat)h;
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-50.0, 50.0, -50.0 / aspect, 50.0 / aspect, -1.0, 1.0);
}

void display() {
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glScalef(10.0, 10.0, 1.0);
    glRotatef(Rotationswinkel, 0.0, 0.0, 1.0);
    glBegin(GL_TRIANGLES);
    glColor3f(1, 0, 0); glVertex3f(0, 2, 0);
    glColor3f(0, 1, 0); glVertex3f(-1, 0, 1);
    glColor3f(0, 0, 1); glVertex3f(1, 0, 1);
    glEnd();

    glFlush();
}

void timer(int v) {
        Rotationswinkel += 1.0;
        glutPostRedisplay();
        glutTimerFunc(Animationsverzögerung, timer, v);
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE);
    glutInitWindowSize(800, 600);
    glutCreateWindow("drehendes Dreieck");
    glutReshapeFunc(reshape);
    glutDisplayFunc(display);
    glutTimerFunc(0, timer, 0);
    glutMainLoop();
}