---

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') { if (Angle < 180.0) Angle = Angle + 5.0; }
    if (key == 's') { if (Angle > 0.0) Angle = Angle - 5.0; }
    glutPostRedisplay();
}

void myDisplay() {
    glClear(GL_COLOR_BUFFER_BIT);
    drawHalfCircle();
    drawArrow();
    glutSwapBuffers();
}

void myInit() {
    glClearColor(1, 1, 1, 0);
    glColor3f(0, 0, 0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-320, 320, -320, 320);
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(640, 640);
    glutCreateWindow("Lab2: Half circle with arrow");
    glutDisplayFunc(myDisplay);
    glutTimerFunc(50, timer, 0);
    glutKeyboardFunc(Keyboard);
    myInit();
    glutMainLoop();
    return 0;
}

draw.h
#ifndef DRAW_H
#define DRAW_H

extern float Angle;
extern float r;

void drawHalfCircle();
void drawArrow();

#endif

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(1.0, 0.0, 0.0);
    glVertex2f(0.0, r - 50.0);
    glVertex2f(0.0, -(r - 50.0));
    glEnd();
    
    glPopMatrix();
}

void drawHalfCircle() {
    glColor3f(0, 0, 0);
    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();
    }
}