#include <glad/glad.h>
#include <GLFW/glfw3.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow* window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;


int main()
{
	// 初始化 GLFW
	glfwInit();
	// 配置 GLFW : 版本 3.3 ,使用 Core-profile 模式 
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

// MACOS 平台需要启用这一条
#ifdef _APPLE_
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif // _APPLE_

	// 创建窗口对象
	GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
	if (window == NULL)
	{
		std::cout << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);
	// 注册帧缓冲变化时的回调函数
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

	// 初始化 GLAD : load all OpenGL function pointers
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}

	// 渲染循环 (Render Loop)
	while (!glfwWindowShouldClose(window))
	{
		// input
		processInput(window);

		// 渲染指令
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);	// 状态设置函数
		glClear(GL_COLOR_BUFFER_BIT);			// 状态使用函数

		// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
		glfwSwapBuffers(window);
		glfwPollEvents();
	}

	// glfw: terminate, clearing all previously allocated GLFW resources
	glfwTerminate();

	return 0;
}

// 窗口大小改变时的回调函数
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
	// 视口
	glViewport(0, 0, width, height);
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
void processInput(GLFWwindow* window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
		glfwSetWindowShouldClose(window, true);
}