#include <GL/gl.h>
#include <GL/glut.h>
#include <cmath>

using std::cos;
using std::sin;

#define SCALE_MIN 0.1f
#define SCALE_MAX 10.0f
#define SCALE_MOD 1.1f
#define NUM_STEPS 32
#define PI		  3.141592654f

char color = 'r';
char howtodraw = 'l';
float scale = 1.0f;
float colorVal = 0.5f;

int button = 0;
int xprev = 0;
int yprev = 0;

void display()
{
	glClear(GL_COLOR_BUFFER_BIT);

	glLoadIdentity();

	switch(color)
	{
		case 'r':
			glColor3f(colorVal, 0.0f, 0.0f);
			break;

		case 'b':
			glColor3f(0.0f, 0.0f, colorVal);
			break;

		case 'g':
			glColor3f(0.0f, colorVal, 0.0f);
			break;
	}

	switch(howtodraw)
	{
		case 'l':
			glBegin(GL_LINE_STRIP);
			break;

		case 'p':
			glBegin(GL_TRIANGLE_FAN);
			glVertex3f(0.0f, 0.0f, 0.0f);
			break;
	}

	for(int i = 0; i <= NUM_STEPS; ++i)
	{
		float a = 2*i*PI/NUM_STEPS;
		float x = scale*cos(a);
		float y = scale*sin(a);

		glVertex3f(x, y, 0.0f);
	}

	glEnd();

	glutSwapBuffers();
}

void reshape(int x, int y)
{
	glViewport(0, 0, x, y);
}

void keyboard(unsigned char key, int x, int y)
{
	switch(key)
	{
		case 'c':
		case 'C':
			if(color == 'r')		color = 'g';
			else if(color == 'g')	color = 'b';
			else					color = 'r';

			break;

		case 'r':
		case 'R':
			if(howtodraw == 'l')	howtodraw = 'p';
			else					howtodraw = 'l';

			break;
	}

	glutPostRedisplay();
}

void mouse(int b, int state, int x, int y)
{
	if(state == GLUT_DOWN)
	{
		button = b;
	   	xprev = x;
		yprev = y;
	}
	else
	{
		button = 0;
	}
}

void mouseMotion(int x, int y)
{
	int d = x - xprev;

	if(button == GLUT_LEFT_BUTTON)
	{
		if(d > 0)
		{
			scale *= pow(SCALE_MOD, d);
		}
		else
		{
			scale /= pow(SCALE_MOD, -d);
		}

		if(scale < SCALE_MIN)	scale = SCALE_MIN;
		if(scale > SCALE_MAX)	scale = SCALE_MAX;
	}

	if(button == GLUT_RIGHT_BUTTON)
	{
		if(d > 0)
		{
			colorVal += 0.02f;
		}
		else
		{
			colorVal -= 0.02f;
		}

		if(colorVal > 1.0f)	colorVal = 1.0f;
		if(colorVal < 0.0f) colorVal = 0.0f;
	}

	xprev = x;
	yprev = y;

	glutPostRedisplay();
}

void initGL()
{
	glClearColor(0.0, 0.0, 0.0, 0.0);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-10.0, 10.0, -10.0, 10.0, -1.0, 1.0);

	glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char *argv[])
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);

	glutInitWindowPosition(200, 200);
	glutInitWindowSize(500, 500);

	int win = glutCreateWindow("OpenGL demo");

	initGL();

	glutDisplayFunc(display);
	glutReshapeFunc(reshape);
	glutKeyboardFunc(keyboard);
	glutMouseFunc(mouse);
	glutMotionFunc(mouseMotion);

	glutMainLoop();

	return 0;
}