---

main.cpp
#include "glut.h"
#include <math.h>
#include "draw.h"

float r = 200.0;
float Angle = 0.0;

void timer(int) {
    glutPostRedisplay();
    glutTimerFunc(50, timer, 0);
}

void Keyboard(unsigned char key, int x, int y) {
    if (key == 'w') Angle += 5.0;
    if (key == 's') Angle -= 5.0;
    glutPostRedisplay();
}

void myDisplay() {
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();
    glRotatef(-45.0, 0.0, 0.0, 1.0);

    drawHalfCircle();
    drawArrow();

    glPopMatrix();
    glutSwapBuffers();
}

void myInit() {
    glClearColor(1, 1, 1, 0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-320, 320, -320, 320);
    glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(640, 640);
    glutCreateWindow("Lab2");
    glutDisplayFunc(myDisplay);
    glutTimerFunc(50, timer, 0);
    glutKeyboardFunc(Keyboard);
    myInit();
    glutMainLoop();
    return 0;
}
draw.cpp
#include "glut.h"
#include "draw.h"
#include <math.h>
#define PI 3.14159265f

void drawArrow() {
    glPushMatrix();
    glRotatef(Angle, 0.0, 0.0, 1.0);

    glBegin(GL_LINES);
    glColor3f(1.0f, 0.0f, 0.0f);
    glVertex2f(0.0f, 40.0f);
    glVertex2f(0.0f, -40.0f);
    glEnd();

    glPopMatrix();
}

void drawHalfCircle() {
    glColor3f(0.0f, 0.0f, 0.0f);
    glBegin(GL_LINE_STRIP);
    for (float i = 0; i <= PI; i += PI / 200.0f) {
        glVertex2f(r * cos(i), r * sin(i));
    }
    glEnd();

    for (float i = 0; i <= PI; i += PI / 6.0f) {
        glBegin(GL_LINES);
        glVertex2f((r + 15.0f) * cos(i), (r + 15.0f) * sin(i));
        glVertex2f((r - 15.0f) * cos(i), (r - 15.0f) * sin(i));
        glEnd();
    }
}
draw.h
#ifndef DRAW_H
#define DRAW_H

extern float Angle;
extern float r;

void drawHalfCircle();
void drawArrow();

#endif