#include <glad\glad.h>
#include <GLFW\glfw3.h>
#include <iostream>

const unsigned int WINDOW_WIDTH = 800;
const unsigned int WINDOW_HEIGHT = 600;

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

//頂點著色器有兩個屬性 座標和顏色

const char* vertexShaderSource = "#version 330 core\n"
"layout(location=0)in vec3 aPos;\n"
"layout(location=1)in vec3 aColor;\n"
"out vec3 outColor;\n"
"void main(){\n"
"gl_Position=vec4(aPos,1.0);\n"
"outColor=aColor;\n"
"}\n\0";

//頂點著色器的輸出為片段著色器的輸入 保持型別和欄位名一致就可以

const char* fragmentShaderSource = "#version 330 core\n"
"out vec4 fragColor;\n"
"in vec3 outColor;\n"
"void main(){\n"
"fragColor = vec4(outColor,1.0f);\n"
"}\n";


int main()
{

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

#ifdef __APPLE__
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // uncomment this statement to fix compilation on OS X
#endif

	GLFWwindow* window = glfwCreateWindow(WINDOW_WIDTH, WINDOW_HEIGHT, "Zhongqi", NULL, NULL);
	if (window == NULL)
	{
		std::cout << "Create Window Error\n" << std::endl;
		glfwTerminate();
		return -1;
	}

	glfwMakeContextCurrent(window);
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		return -1;
	}

	//建立頂點著色器
	int vertexShader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
	glCompileShader(vertexShader);
	int success;
	char infoLog[512];
	glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
	if (!success)
	{
		glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
		std::cout << "GL COMPILE ERROR\n" << infoLog << std::endl;

	}
	
	//建立片段著色器
	int  fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
	glCompileShader(fragmentShader);
	glGetShaderiv(fragmentShader, GL_COMPILE_STATUS,&success);
	if (!success)
	{
		glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
		std::cout << "GL COMPILE ERROR\n" << infoLog << std::endl;
	}


	//建立著色器程式
	int shaderPrograme = glCreateProgram();
	glAttachShader(shaderPrograme, vertexShader);
	glAttachShader(shaderPrograme,fragmentShader);
	glLinkProgram(shaderPrograme);
	glGetProgramiv(shaderPrograme, GL_LINK_STATUS, &success);
	if (!success)
	{
		glGetProgramInfoLog(shaderPrograme, 512, NULL, infoLog);
		std::cout << "GL INFOLOG " << infoLog << std::endl;
	}

	glDeleteShader(vertexShader);
	glDeleteShader(fragmentShader);

	//建立頂點資料
	float firstTrangles[] = {
	 //座標           顏色
	 -0.5f,-0.5f,0.0f,1.0f,0.0f,0.0f,
	 0.5f,-0.5f,0.0f,0.0f,1.0f,0.0f,
     0.0f,0.5f,0.0f,0.0f,0.0f,1.0f,
	};

	unsigned int VAO, VBO;
	glGenVertexArrays(1, &VAO);
	glGenBuffers(1, &VBO);

	glBindVertexArray(VAO);
	glBindBuffer(GL_ARRAY_BUFFER, VBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(firstTrangles), firstTrangles, GL_STATIC_DRAW);
	
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float),(void*)0);
	glEnableVertexAttribArray(0);

	glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(3*sizeof(float)));
	glEnableVertexAttribArray(1);


	while (!glfwWindowShouldClose(window))
	{

		processInput(window);
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		glUseProgram(shaderPrograme);
		glBindVertexArray(VAO);
		glDrawArrays(GL_TRIANGLES, 0, 3);

		glfwSwapBuffers(window);
		glfwPollEvents();

	}

	glDeleteVertexArrays(1, &VAO);
	glDeleteBuffers(1, &VBO);
	glfwTerminate();
	return 0;
}

void processInput(GLFWwindow *window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
		glfwSetWindowShouldClose(window, true);
}

void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
	glViewport(0, 0, width, height);
} 
 

效果圖