#include <GL/gl.h>
#include <GL/glut.h>
#include <cstdlib>
#include <ctime>

float randomFloat()
{
    return static_cast<float>(rand()) / static_cast<float>(RAND_MAX);
}

void drawSquare(const float x, const float y, const float size)
{
    glBegin(GL_POLYGON);
    glColor3f(randomFloat(), randomFloat(), randomFloat());
    glVertex2f(x, y);
    glColor3f(randomFloat(), randomFloat(), randomFloat());
    glVertex2f(x + size, y);
    glColor3f(randomFloat(), randomFloat(), randomFloat());
    glVertex2f(x + size, y - size);
    glColor3f(randomFloat(), randomFloat(), randomFloat());
    glVertex2f(x, y - size);
    glEnd();
}

void drawFractal(const int levelsCount, const float randomness, const float x, const float y, const float rectSize)
{
    float singleRectSize = rectSize / 3;

    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            if (i == 1 && j == 1)
                continue;

            if (levelsCount == 0)
                drawSquare(x + i * singleRectSize  + singleRectSize * randomFloat() * randomness, y - j * singleRectSize + singleRectSize * randomFloat() * randomness, singleRectSize);
            else
                drawFractal(levelsCount - 1, randomness, x + i * singleRectSize + singleRectSize * randomFloat() * randomness, y - j * singleRectSize + singleRectSize * randomFloat() * randomness, singleRectSize);
        }
    }
}

void renderScene()
{
    glClear(GL_COLOR_BUFFER_BIT);

    glColor3f(0.0F, 1.0F, 0.0F);

    int levelCount = 2;
    float startX = -75.0F;
    float startY = 75.0F;
    float fractalSize = 150.0F;
    float randomness = 0.05;

    drawFractal(levelCount, randomness, startX, startY, fractalSize);

    glFlush();
}

void changeSize(int width, int height)
{
    if (height == 0)
        height = 1;

    glViewport(0, 0, width, height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    float aspectRatio = static_cast<float>(width) / static_cast<float>(height);

    if (width <= height)
        glOrtho(-100.0, 100.0, -100.0 / aspectRatio, 100.0 / aspectRatio, 1.0, -1.0);
    else
        glOrtho(-100.0 * aspectRatio, 100.0 * aspectRatio, -100.0, 100.0, 1.0, -1.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void myInit()
{
    std::srand(std::time(nullptr));
    glClearColor(0.5F, 0.5F, 0.5F, 1.0F);
}

int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA);
    glutCreateWindow("Dywan Sierpinskiego");

    glutDisplayFunc(renderScene);
    glutReshapeFunc(changeSize);
    myInit();

    glutMainLoop();

    return 0;
}