//
//  main.c
//  FirstOpenGL
//
//  Created by yarpee on 16/1/9.
//  Copyright © 2016年 yarpee. All rights reserved.
//

#include <stdio.h>
//#include <GLUT/GLUT.h>
#define GLEW_STATIC
#include <GL/glew.h>
#include <glfw3.h>

/*void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glBegin(GL_POLYGON);
    glVertex2f(-0.5, -0.5);
    glVertex2f(-0.5, 0.5);
    glVertex2f(0.5, 0.5);
    glVertex2f(0.5, -0.5);
    glEnd();
    glFlush();
}*/

const GLchar* vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 position;\n"
"void main()\n"
"{\n"
"gl_Position = vec4(position.x, position.y, position.z, 1.0f);\n"
"}";

const GLchar* fragmentShaderSource = "#version 330 core\n"
"out vec4 color;\n"
"void main()\n"
"{\n"
"color = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}";

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
    printf("key=%d\n", key);
    if(GLFW_KEY_ESCAPE == key && GLFW_PRESS == action)
    {
        glfwSetWindowShouldClose(window, GL_TRUE);
    }
}

int main(int argc, const char * argv[]) {
    // insert code here...
    printf("Hello, World!\n");
    
    // GLUT
    /*glutInit(&argc, (char**)argv);
    glutCreateWindow("LearningOpenGL");
    glutDisplayFunc(display);
    glutMainLoop();*/
    
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
    
    // For Mac OSX
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    
    GLFWwindow* window = glfwCreateWindow(800, 600, "LearningOpenGL", NULL, NULL);
    if(NULL == window)
    {
        printf("Failed to create GLFW window\n");
        glfwTerminate();
        return -1;
    }
    
    glfwMakeContextCurrent(window);
    glfwSetKeyCallback(window, key_callback);
    
    // For OpenGL core-profile
    glewExperimental = GL_TRUE;
    
    if(glewInit() != GLEW_OK)
    {
        printf("Failed to initialize GLEW\n");
        return -1;
    }
    
    glViewport(0, 0, 800, 600);
    
    // Vertex Shader
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    
    GLint success = 0;
    GLchar infoLog[512] = {0};
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if(!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        printf("Vertex Shader Compile Error, %s\n", infoLog);
    }
    
    // Fragment Shader
    GLuint 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);
        printf("Fragment Shader Compile Error, %s\n", infoLog);
    }
    
    // Link Shaders
    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if(!success)
    {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        printf("Shader Link Error, %s\n", infoLog);
    }
    
    // Delete Shaders
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);
    
    // VAO
    GLuint VAO = 0;
    glGenVertexArrays(1, &VAO);
    
    // 绑定VAO
    glBindVertexArray(VAO);
    
    // Vertices
    /*GLfloat vertices[] =
    {
        0.0f, 0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        -0.5f, -0.5f, 0.0f,
    };*/
    
    // Vertices & Indices
    GLfloat vertices[] =
    {
        0.5f, 0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        -0.5f, -0.5f, 0.0f,
        -0.5f, 0.5f, 0.0f,
    };
    GLuint indices[] =
    {
        0, 1, 3,
        1, 2, 3,
    };
    
    // VBO
    GLuint VBO = 0;
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    
    // EBO
    GLuint EBO = 0;
    glGenBuffers(1, &EBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
    
    // 设置顶点属性
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 3, (GLvoid*)0);
    glEnableVertexAttribArray(0);
    
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    
    // 解绑VAO
    glBindVertexArray(0);
    
    while(!glfwWindowShouldClose(window))
    {
        glfwPollEvents();
        
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        
        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
        
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
        //glDrawArrays(GL_TRIANGLES, 0, 3);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        glBindVertexArray(0);
        
        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
        
        glfwSwapBuffers(window);
    }
    
    // 释放资源
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);
    
    glfwTerminate();
    
    return 0;
}