#include "GL/glut.h"
#include <iostream.h>
#include <math.h>


const int toggle=-1;
enum {source,destination};
int currstate=source;
float curralpha = 0.5;
int factor[2]={GL_ONE,GL_ZERO};

char* fname[4]= {"GL_ZERO", "GL_ONE", "GL_SRC_ALPHA", "GL_ONE_MINUS_SRC_ALPHA"};



int width=500, height=500;
int numcolors=6;
float colors0[7][4] = {
	{1.0,0.0,0.0,0.25},
	{1.0,1.0,0.0,0.25},
	{0.0,1.0,0.0,0.25},
	{0.0,1.0,1.0,0.25},
	{0.0,0.0,1.0,0.25},
	{1.0,0.0,1.0,0.25},
	{1.0,0.0,0.0,0.25},
};
float colors1[7][4] = {
	{1.0,0.0,0.0,0.5},
	{1.0,1.0,0.0,0.5},
	{0.0,1.0,0.0,0.5},
	{0.0,1.0,1.0,0.5},
	{0.0,0.0,1.0,0.5},
	{1.0,0.0,1.0,0.5},
	{1.0,0.0,0.0,0.5},
};
const float points[14][3]= {
	{-120.0,-250.0,-20.0},
	{-120.0,250.0,-20.0},
	{-80.0,-250.0,-20.0},
	{-80.0,250.0,-20.0},
	{-40.0,-250.0,-20.0},
	{-40.0,250.0,-20.0},
	{0.0,-250.0,-20.0},
	{0.0,250.0,-20.0},
	{40.0,-250.0,-20.0},
	{40.0,250.0,-20.0},
	{80.0,-250.0,-20.0},
	{80.0,250.0,-20.0},
	{120.0,-250.0,-20.0},
	{120.0,250.0,-20.0}
};
	


void init();
void display();
void reshape(int w, int h);
void mouse(int button, int state, int x, int y);
void keyboard(unsigned char key, int x, int y);
int round(float x);
void menu(int menuitem);
char* getname(int glcode);

main(int argc, char* argv[])
{
	int mainmenu;
	
	/*  set up window */
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE );
	glutInitWindowSize(width,height);
	glutInitWindowPosition(100,100);
	glutCreateWindow("Blending");

	/* initialize state */
	init();

	/*  set up menus */
	mainmenu=glutCreateMenu(menu);
	glutAddMenuEntry("Toggle to Set Destination Factor",toggle);
	glutAddMenuEntry("GL_Zero",GL_ZERO);
	glutAddMenuEntry("GL_One",GL_ONE);
	glutAddMenuEntry("GL_Src_Alpha",GL_SRC_ALPHA);
	glutAddMenuEntry("GL_One_Minus_Src_Alph",GL_ONE_MINUS_SRC_ALPHA);

	glutAttachMenu(GLUT_RIGHT_BUTTON);


	/* register call back functions */
	glutDisplayFunc(display);
	glutReshapeFunc(reshape);
//	glutMouseFunc(mouse);
	glutKeyboardFunc(keyboard);


	/* wait until something happens */
	glutMainLoop();


	return 1;
}

void init()
{
	/*  clear color is black  */
	glClearColor(0.0,0.0,0.0,0.0);

	/*  define the viewing system */ 
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-250.0, 250.0, -250.0, 250.0, 10.0, 50.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glShadeModel(GL_FLAT);
	
	glEnable(GL_BLEND);
	cerr << "SRC alpha = " << curralpha << "\n";
	cerr << "Source: " << getname(factor[source]) << ", Destination: " << getname(factor[destination]) << "\n";
}
	

void display()
{
	int i;

	glClear(GL_COLOR_BUFFER_BIT);

	// draw the bottom pallette
	glBlendFunc(GL_ONE,GL_ZERO);
	glBegin(GL_QUAD_STRIP);
		for(i= 0; i<=numcolors; i += 1) {
			glColor4fv(&colors0[i][0]);
			glVertex3fv(&points[2*i][0]);
			glVertex3fv(&points[2*i+1][0]);
		}
	glEnd();

	glBlendFunc(factor[source],factor[destination]);

	glPushMatrix();
		glRotatef(90.0,0.0,0.0,1.0);
		glBegin(GL_QUAD_STRIP);
			for(i= 0; i<=numcolors; i += 1) {
			glColor4fv(&colors1[i][0]);
			glVertex3fv(&points[2*i][0]);
			glVertex3fv(&points[2*i+1][0]);
		}
		glEnd();
	glPopMatrix();

	glutSwapBuffers();

}

void reshape(int w, int h)
{
	/* width and height store current window dimensions */
	width = w;
	height = h;
	
	/*  map the projection plane to the entire window */
	glViewport(0,0,w,h);


}

void keyboard(unsigned char key, int x, int y)
{
	int i;

	switch(key) {

	// add new points
	case '+':
		if (curralpha < 1.0) {
			curralpha += (float) 0.05;
			for (i=0;i<=numcolors;i++)
				colors1[i][3]=curralpha;
		}
		cerr << "SRC Alpha = " << curralpha << "\n";
		glutPostRedisplay();
		break;

	case '-':
		if (curralpha > 0.0) {
			curralpha -= (float) 0.05;
			for (i=0;i<=numcolors;i++)
				colors1[i][3]=curralpha;
		}
		cerr << "SRC Alpha = " << curralpha << "\n";
		glutPostRedisplay();
		break;		
		break;
	}

	return;
}

void menu(int menuitem)
{
	switch(menuitem) {

	case toggle:
		if (currstate==source) {
			glutChangeToMenuEntry(1,"Toggle to Set Source Factor",toggle);
			currstate=destination;
			
		}
		else {
			glutChangeToMenuEntry(1,"Toggle to Set Destination Factor",toggle);
			currstate=source;
		}
		break;

	default:
		factor[currstate]=menuitem;
		cerr << "Source: " << getname(factor[source]) << ", Destination: " << getname(factor[destination]) << "\n";
		glutPostRedisplay();
		break;


	}
			
	return;
}

char* getname(int glcode)
{
	switch (glcode) {
	case GL_ZERO:
		return fname[0];
	case GL_ONE:
		return fname[1];
	case GL_SRC_ALPHA:
		return fname[2];
	case GL_ONE_MINUS_SRC_ALPHA:
		return fname[3];
	}
	return "";
}