OpenGL 기반 중력/속도/가속도 예제(ball)-17년 3월 6일 수정

#include <cmath>

#include <ctime>

#include <cstdlib>

#include <iostream>

#include <sstream>

#include <string>

#include <GL/glut.h>

using namespace std;

const double pi = 4 * atan(1.0);

const double gravity = 9.8;

const int width = 640;

const int height = 480;

const double velocityMax = 1; //Maxium inital speed

class Ball {

public : 

double x, y, vx, vy;

double velocity = 0.0;

double acceleration = 0.1;

Ball(double x, double vx, double y, double vy) {

this->x = x;

this->vx = vx;

this->y = y;

this->vy = vy;

}

// Randomly move to any neighboring pixel (or stay in the same spot)

void step() {

x += vx*acceleration;

y += vy*acceleration;

vx = vx;

vy -= gravity*acceleration;

        if (x >  width) vx = -abs(vx);     // x limit(high)

        if (x < 0) vx = abs(vx);       // x limit(low)

if (y > height) vy = -abs(vy);         // y limit(high)

        if (y < 0) vy = abs(vy);       // y limit(low)

}

};

Ball *ball;

void create_ball() {

double theta = pi * rand() / double(RAND_MAX);

    ball = new Ball(0, velocityMax * cos(theta),

0, velocityMax * sin(theta));

}

void drawText(const string &str, double x, double y) {

    glRasterPos2d(x, y);

    int len = str.find('\0');

    for (int i = 0; i < len; i++)

       glutBitmapCharacter(GLUT_BITMAP_HELVETICA_12, str[i]);

}

// move each ball by one time step dt

void step() {

    ball->step();

    ball->velocity += ball->acceleration;

}

void animation_step() {

double frames_per_second = 30;   // for animation in real time

    double start = ball->velocity;

    clock_t start_time = clock();

    step();

    double tau = 1.0 / frames_per_second;

    while (ball->velocity - start < tau)

        step();

    while ((double(clock()) - start_time)/CLOCKS_PER_SEC < tau)

        ;

    glutPostRedisplay();

}

// Glut callback function to update the display

void display() {

    glClear(GL_COLOR_BUFFER_BIT);

    static GLubyte color_table[6][3] =

        {{255, 0, 0}, {0, 255, 0}, {0, 0, 255},

         {0, 255, 255}, {255, 0, 255}, {255, 255, 0}}; // Red, Green, Blue, Sky, Purple, Yellow

glColor3ubv(color_table[0]);

//glPointSize(10);

glBegin(GL_TRIANGLE_FAN);

glVertex2d(ball->x, ball->y);

double phi = 2 * pi / 24;

        for (int j = 0; j < 25; j++)

                glVertex2d(ball->x + 10 * cos(phi*j),

                           ball->y + 10 * sin(phi*j));

glEnd();

    glColor3ub(0, 0, 0);

    ostringstream os;

    os << "velocity: " << ball->velocity << "x pos: " << ball->x << "   y pos " << ball->y << ends;

    drawText(os.str(), 12, 24);

    os.seekp(0);

    glutSwapBuffers();

}

// Glut callback function to reset the viewing transformation

void reshape(int w, int h) {

    glViewport(0, 0, w, h);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    glOrtho( 0.0, 640.0, 0.0, 480.0, 1.0, -1.0 );

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

}

bool running = false;   // is the animation running

// Glut mouse callback function

void mouse(int button, int state, int x, int y) {

    switch (button) {

    case GLUT_LEFT_BUTTON:

        if (state == GLUT_DOWN) {

            if (running) {

                glutIdleFunc(NULL);

                running = false;

            } else {

                glutIdleFunc(animation_step);

                running = true;

            }

        }

    }

}

int main(int argc, char *argv[]) {

    glutInit(&argc, argv);

    create_ball();

    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);

    glutInitWindowSize(width, height);

    glutInitWindowPosition(100, 100);

    glutCreateWindow("Walker");

    glClearColor(1.0, 1.0, 1.0, 0.0);

    glShadeModel(GL_FLAT);

    glutDisplayFunc(display);

    glutReshapeFunc(reshape);

    glutMouseFunc(mouse);

    glutMainLoop();

}