OpenGL-Animated-Circles.cpp

#include <gl/glut.h>
#include <math.h>

struct Point {
	GLint x;
	GLint y;
};

void init() {
	glClearColor(1.0, 1.0, 1.0, 0.0);
	glColor3f(0.0f, 0.0f, 0.0f);
	glPointSize(1.0f);
	gluOrtho2D(0.0f, 640.0f, 0.0f, 480.0f);
}

void draw_circle(Point pC, GLfloat radius) {
	GLfloat step = 1/radius;
	GLfloat x, y;

	for(GLfloat theta = 0; theta <= 360; theta += step) {
		x = pC.x + (radius * cos(theta));
		y = pC.y + (radius * sin(theta));
		glVertex2i(x, y);
	}
}


Point pCenter = {320, 240};
float dRadius = 1;

float radius[3] = {
	0.0f,
	60.0f,
	120.0f
};

void display(void) {
	glClear(GL_COLOR_BUFFER_BIT);
	glBegin(GL_POINTS);
		for(int i = 0; i < 3; i++) {
			draw_circle(pCenter, radius[i]);
			radius[i]+=dRadius;

			if(radius[i] > 180)
				radius[i] = 0;
		}
	glEnd();
	glFlush();
}

void Timer(int value) {
	glutTimerFunc(33, Timer, 0);
	glutPostRedisplay();
}

int main(int argc, char **argv) {
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowPosition(200, 200);
	glutInitWindowSize(640, 480);
	glutCreateWindow("Square");
	glutDisplayFunc(display);
	init();
	Timer(0);
	glutMainLoop();

	return 0;
}