main.cpp

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

#include <iostream>
#include <cmath>
#include <fstream>
#include <sstream>

// #include "Renderer.hpp"

#define ASSERT(x) if (!(x))   // this is very hackedtogether ... luki probiert aus
#define GLCall(x) GLClearError();\
	x;\
	ASSERT(GLLogCall(#x, __FILE__, __LINE__))	

// hallo jakob! 
// also check /res/shaders/basic.shader

// error stuff (old method)
static void GLClearError()
{
	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;
}

// shader stuff - read shaders from file etc
struct ShaderProgramSource
{
	std::string VertexSource;
	std::string FragmentSource;
};

static ShaderProgramSource ParseShader(const std::string& filepath)
{
	std::ifstream stream(filepath);
	if (!stream.is_open()) std::cout << "COULD NOT FIND SHADER FILE!\n";

	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)
			{
				type = ShaderType::VERTEX;
			}
			else if (line.find("fragment") != std::string::npos)
			{
				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);
		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 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);

	return program;
}

int main(void)
{
	GLFWwindow* window;

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

	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	/* Create a windowed mode window and its OpenGL context */
	window = glfwCreateWindow(720, 720, "some window", NULL, NULL);
	if (!window)
	{
		glfwTerminate();
		return -1;
	}

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

	glfwSwapInterval(1);

	// extra
	if (glewInit() == GLEW_OK){
		std::cout << "GLEW is Alright!!!\n";
	}
	else {
		std::cout << "GLEW has an Error!!!\n";
	};

	std::cout << "openGL version: " << glGetString(GL_VERSION) << std::endl;

	float positions[8] = {
		 -0.5f, -0.5f,
		  0.5f, -0.5f,
		  0.5f,  0.5f,
		 -0.5f,  0.5f
	};

	// maybe unsigned short? if only few vertices -> faster?
	unsigned int indices[] = {
		0, 1, 2,
		2, 3, 0
	};

	// create vertex array object
	unsigned int vao;
	GLCall(glGenVertexArrays(1, &vao));
	GLCall(glBindVertexArray(vao));

	// create vertex buffer
	unsigned int buffer;
	GLCall(glGenBuffers(1, &buffer));
	GLCall(glBindBuffer(GL_ARRAY_BUFFER, buffer));
	GLCall(glBufferData(GL_ARRAY_BUFFER, 4 * 2 * sizeof(float), positions, GL_STATIC_DRAW));

	// specify vertex buffer layout, bind attributes to certain index e.g. x-coordinate is at index 0 of vertex.
	GLCall(glEnableVertexAttribArray(0));
	GLCall(glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), 0));

	// create index buffer
	unsigned int ibo; // ibo = index buffer object
	GLCall(glGenBuffers(1, &ibo));
	GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo));
	GLCall(glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(unsigned int), indices, GL_STATIC_DRAW));


	ShaderProgramSource source = ParseShader("../res/shaders/basic.shader"); 	
	unsigned int shader = CreateShader(source.VertexSource, source.FragmentSource);
	GLCall(glUseProgram(shader));
	
	std::cout << "VERTEX" << std::endl;
	std::cout << source.VertexSource << std::endl;
	std::cout << "FRAGMENT" << std::endl;
	std::cout << source.FragmentSource << std::endl;

	GLCall(glBindVertexArray(0));
	GLCall(glUseProgram(0));
	GLCall(glBindBuffer(GL_ARRAY_BUFFER, 0));
	GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0));	


	int location = glGetUniformLocation(shader, "u_Color");

	float r = 0.0f;
	float g = 0.0f;
	float b = 0.0f;
	float r_increment = 0.035f;
	float g_increment = 0.0335f;
	float b_increment = 0.0475f;

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

		GLCall(glUseProgram(shader));
		GLCall(glUniform4f(location, r, g, b, 1.0f));

		GLCall(glBindVertexArray(vao));
		GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo));

		GLCall(glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr)); // with index buffer, MUST be UNSIGNED 

		if (r > 1.0f)
			r_increment = -0.05f;
		else if (r < 0.0f )
			r_increment = 0.01f;
		r += r_increment;

		if (g > 1.0f)
			g_increment = -0.05f;
		else if (r < 0.0f )
			g_increment = 0.01f;
		g += g_increment;

		if (b > 1.0f)
			b_increment = -0.05f;
		else if (r < 0.0f )
			b_increment = 0.01f;
		b += b_increment;


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

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

	// glDeleteProgram(shader);

	glfwTerminate();
	return 0;
}