pre uniform

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

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

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

#ifdef DEBUG
    #define GLCall(x) GLClearError(); x; ASSERT(GLLogCall(...))
#else
    #define GLCall(x) x
#endif

static void GLClearError() {
    while (glGetError() != GL_NO_ERROR);    // clear all the errors
}

static void GLCheckError() {
    while (GLenum error = glGetError()) {
        std::cout << "[OpenGL_Error] (" << error << ")" << std::endl;
    }
}

// returns true if no error
static bool GLLogCall(const char* function, const char* file, int line) {
    if (GLenum error = glGetError()) {
        std::cout << "[OpenGL_Error] (" << error << ")" << std::endl;
        std::cout << 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 (std::getline(stream, line)) {
        if (line.find("#shader") != std::string::npos) {
            if (line.find("vertex") != std::string::npos)
                type = ShaderType::VERTEX;
            else if(line.find("fragment") != std::string::npos)
                type = ShaderType::FRAGMENT;
        }
        else {
            ss[(int)type] << line << '\n';
        }
    }
    std::cout << "here" << std::endl;
    //return { ss[(int)ShaderType::VERTEX].str(), ss[(int)ShaderType::FRAGMENT].str() };
    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);
        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << "Failed to compile " << ((type == GL_VERTEX_SHADER) ? "vertex" : "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);

    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;

    float positions[12] = {
        -0.5f, -0.5f,   // 0
         0.5f, -0.5f,   // 1
         0.5f,  0.5f,   // 2
        -0.5f,  0.5f,   // 3
    };

    unsigned int indices[6] = {
        0, 1, 2,
        2, 3, 0
    };

    unsigned int buffer;
    GLCall(glGenBuffers(1, &buffer));
    GLCall(glBindBuffer(GL_ARRAY_BUFFER, buffer));
    GLCall(glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW));

    GLCall(glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0));
    GLCall(glEnableVertexAttribArray(0));

    unsigned int ibo;
    GLCall(glGenBuffers(1, &ibo));
    GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo));
    GLCall(glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW));

    shaderProgramSource src = parseShader("Basic.shader");
    std::cout << "VERTEX" << std::endl;
    std::cout << src.vertexSource << std::endl;
    std::cout << "FRAGMENT" << std::endl;
    std::cout << src.fragmentSource << std::endl;

    unsigned int shader = createShader(src.vertexSource, src.fragmentSource);
    GLCall(glUseProgram(shader));

    int location = GLCall(glGetUniformLocation(shader, "u_Color"));
    ASSERT(location != -1);
    GLCall(glUniform4f(location, 0.2f, 0.3f, 0.8f, 0.7f));

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

        //glDrawArrays(GL_TRIANGLES, 0, 6);
        //GLClearError();
        GLCall(glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr));
        /*GLCheckError();
        ASSERT(GLLogCall());*/

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

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

    glDeleteProgram(shader);

    glfwTerminate();
    return 0;
}