OpenGL Video 10

/*
* OPEN GL DOCUMENTATION SITE: http://docs.gl/
* PUNO PUNO PUNO DOBAR SAJT ZA OPENGL TUTORIALE: http://www.opengl-tutorial.org/beginners-tutorials/tutorial-2-the-first-triangle/ OVO MORAS PROVJERAVATI STALNO.
*/

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>

#define ASSERT(x) if (!(x)) __debugbreak();

// ovdje pravim macro koji ce automatski zovnuti clear error funkciju itd. svaki put kad se dogodi error
// znaci u ovom slucaju pravim macro koji se zove "GLCall" koji prima x (x je funkcija)
// poziva se prvo "GLClearError", i onda ide backslash "\" da bi mogao nastaviti pisati ispod macro, jer bi bilo previse sve u liniji napisati.
// zatim ide x (to je nasa funckija koju smo proslijedili
// kad pozivamo funkciju (tj. x) trebamo proslijediti 3 paramentra
// kad uradimo "#x" to znaci da cemo uraditi x.ToString(), tkao cemo dobiti ime funkcije
// VELIKI NOTE: Cherno kaze da on SVAKU openGl funkciju wrapa u ovaj call, tako da bi trebao to zapamtiti da je best practice to (ne radi meni - makar na poslu)
#define GLCall(x) GLClearError();\
    x;\
    ASSERT(GLLogCall(#x, __FILE__, __LINE__))

static void GLClearError()
{
    // while (!glGetError()); // Can be done like this as well
    while (!glGetError() != GL_NO_ERROR);
}

static bool GLLogCall(const char* function, const char* file, int line)
{
    while (GLenum error = glGetError())
    {
        std::cout << "[OpenGl error] (" << error << "): " << function << " " << file << ":" << line << std::endl;
        return false;
    }
    return true;
}

struct ShaderProgramSource
{
    std::string VertexSource;
    std::string FragmentSource;
};

static ShaderProgramSource ParseShader(const std::string& filepath)
{
    std::ifstream stream(filepath);

    enum class ShaderType
    {
        NONE = -1,
        VERTEX = 0,
        FRAGMENT = 1
    };

    std::string line;
    std::stringstream ss[2];
    ShaderType type = ShaderType::NONE;
    while (getline(stream, line))
    {
        if (line.find("#shader") != std::string::npos)
        {
            if (line.find("vertex") != std::string::npos)
            {
                // set type to vertex
                type = ShaderType::VERTEX;
            }
            else if (line.find("fragment") != std::string::npos)
            {
                // set type to fragment
                type = ShaderType::FRAGMENT;
            }
        }
        else
        {
            ss[(int)type] << line << '\n';
        }
    }
    return {ss[0].str(), ss[1].str()};
}

static unsigned int CompileShader(unsigned int type, const std::string& source)
{
    unsigned int id = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);

    // Error handling
    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE)
    {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);

        // On govori ovdje da hoce na stacku da napravi char array, nece pokazivac koji bi bio na heap-u jer ga mora kasnije pocistiti.
        // Ja se ne slazem sa njim, ali da bi mi bilo lakse pratiti video-e i ja cu napraviti kao i on.
        // char* message = new char[length];

        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << "Failed to compile " <<
            (type == GL_VERTEX_SHADER ? "vertext" : "fragment")
            << " shader." << std::endl;
        std::cout << message << std::endl;
        glDeleteShader(id);
        return 0;
    }

    return id;
}

static unsigned int CreateShader(const std::string& vertexShader, const std::string& fragmentShader)
{
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);

    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);

    // delete intermediates
    glDeleteShader(vs);
    glDeleteShader(fs);

    return program;
}


int main(void)
{
    GLFWwindow* window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent(window);

    if (glewInit() != GLEW_OK)
    {
        std::cout << "Error!" << std::endl;
    }

    std::cout << glGetString(GL_VERSION) << std::endl;

    // Vertex buffers and layouts in open GL
    /*float positions[6] = {
    -0.5f, -0.5f,
    0.0f, 0.5f,
    0.5f, -0.5f
    };*/
    float positions[] = {
        -0.5f, -0.5f, // 0
        0.5f, -0.5f, // 1
        0.5f, 0.5f, // 2
        -0.5f, 0.5f // 3
    };

    unsigned int indices[] = {
        0, 1, 2,
        2, 3, 0
    };

    // Stari array of vertexes nacin crtanja trougla
    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    // Ovdje je prije bilo za 2gi parametar samo "6 * sizeof(float)", ali to je zato sto je bilo 6 tacaka koje treba nacrtati
    glBufferData(GL_ARRAY_BUFFER, 6 * 2 * sizeof(float), positions, GL_STATIC_DRAW);
    // Vertex attributes and layouts in open GL
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
    glEnableVertexAttribArray(0);

    // INDEX BUFFER
    unsigned int ibo;
    glGenBuffers(1, &ibo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(unsigned int), indices, GL_STATIC_DRAW);

    // Creating shaders
    ShaderProgramSource source = ParseShader("res/shaders/Basic.shader");
    unsigned int shader = CreateShader(source.VertexSource, source.FragmentSource);
    glUseProgram(shader);


    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        // Legacy (Old) OpenGl triangle drawing
        //glBegin(GL_TRIANGLES);
        //glVertex2f(-0.5f, -0.5f);
        //glVertex2f(0.0f, 0.5f);
        //glVertex2f(0.5f, -0.5f);
        //glEnd();

        // Crtanje sa nizovima vertexa
        // Za trougao bio treci parametar "3"
        // glDrawArrays(GL_TRIANGLES, 0, 6);

        // Index buffer crtanje
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

        // GLCall(glDrawElements(GL_TRIANGLES, 6, GL_INT, nullptr)); // uncomment to test error func

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    // Delete shader in the end
    glDeleteProgram(shader);

    glfwTerminate();
    return 0;
}