/* 3-d serpinsky gasket
 *
 * Akshay Oppiliappan
 */

#include <GL/glut.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

typedef float point[3];

point tetra[4] = {
    {0, 250, -250},
    {0, 0, 250},
    {250, -250, 250},
    {-250, -250, -250},
};

void myInit() {
    glClearColor(1.0, 1.0, 1.0, 1.0);
    glOrtho(-300.0, 300.0, -300.0, 300.0, -300.0, 300.0);
};

void drawTriangle(point p1, point p2, point p3) {
    glBegin(GL_TRIANGLES);
    glVertex3fv(p1);
    glVertex3fv(p2);
    glVertex3fv(p3);
    glEnd();
}

void drawTetra(point p1, point p2, point p3, point p4) {
    glColor3f(1.0, 1.0, 0.0);
    drawTriangle(p1, p2, p3);

    glColor3f(0.0, 1.0, 0.0);
    drawTriangle(p1, p3, p4);

    glColor3f(1.0, 0.0, 0.0);
    drawTriangle(p1, p4, p2);

    glColor3f(0.0, 0.0, 1.0);
    drawTriangle(p2, p3, p4);
}

void divideTetra(point p1, point p2, point p3, point p4, int iter) {
    point mid[6];
    int j;

    if (iter > 0) {
        for (j = 0; j < 3; j++)
            mid[0][j] = (p1[j] + p2[j]) / 2;
        for (j = 0; j < 3; j++)
            mid[1][j] = (p1[j] + p3[j]) / 2;
        for (j = 0; j < 3; j++)
            mid[2][j] = (p1[j] + p4[j]) / 2;
        for (j = 0; j < 3; j++)
            mid[3][j] = (p2[j] + p3[j]) / 2;
        for (j = 0; j < 3; j++)
            mid[4][j] = (p3[j] + p4[j]) / 2;
        for (j = 0; j < 3; j++)
            mid[5][j] = (p2[j] + p4[j]) / 2;

        divideTetra(p1, mid[0], mid[1], mid[2], iter - 1);
        divideTetra(mid[0], p2, mid[3], mid[5], iter - 1);
        divideTetra(mid[1], mid[3], p3, mid[4], iter - 1);
        divideTetra(mid[2], mid[4], p4, mid[5], iter - 1);
    } else {
        drawTetra(p1, p2, p3, p4);
    }
}

void display() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBegin(GL_TRIANGLES);
    divideTetra(tetra[0], tetra[1], tetra[2], tetra[3], 5);
    glEnd();
    glFlush();
}

int main(int argc, char *argv[]) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(600, 600);
    glutInitWindowPosition(0, 0);
    glutCreateWindow("Sierpinski Gasket");
    glutDisplayFunc(display);
    glEnable(GL_DEPTH_TEST);
    myInit();
    glutMainLoop();
}