triangle

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

#include <vector>
#include <algorithm>

#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;

const char* vertexShaderSource = R"####(
	#version 330 core

	const vec2 vertices[3] = vec2[3](
		vec2(-1.0, -1.0),
		vec2( 3.0, -1.0),
		vec2(-1.0,  3.0)
	);

	void main()
	{
		gl_Position = vec4(vertices[gl_VertexID] * 0.1, 0.0, 1.0);
	}
)####";

const char* fragmentShaderSource = R"####(
	#version 330 core
	out vec4 fragColor;
	void main() {
		fragColor = vec4(1.0, 0.0, 0.0, 1.0);
	}
)####";


uint32_t vao;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    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

    // glfw window creation
    // --------------------
    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);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

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

#undef max
#undef min

	glGenVertexArrays(1, &vao);

	int shaderProgram = 0;
	{
		// build and compile our shader program
		 // ------------------------------------
		 // vertex shader
		int vertexShader = glCreateShader(GL_VERTEX_SHADER);
		glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
		glCompileShader(vertexShader);
		// check for shader compile errors
		int success;
		char infoLog[512];
		glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
		if (!success)
		{
			glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
			std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
		}
		// fragment shader
		int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
		glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
		glCompileShader(fragmentShader);
		// check for shader compile errors
		glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
		if (!success)
		{
			glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
			std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
		}
		// link shaders
		shaderProgram = glCreateProgram();
		glAttachShader(shaderProgram, vertexShader);
		glAttachShader(shaderProgram, fragmentShader);
		glLinkProgram(shaderProgram);
		// check for linking errors
		glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
		if (!success) {
			glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
			std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
		}
		glDeleteShader(vertexShader);
		glDeleteShader(fragmentShader);
	}

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

		glBindVertexArray(vao);
		glUseProgram(shaderProgram);
		glDrawArrays(GL_TRIANGLES, 0, 3);
		glUseProgram(0);
		glBindVertexArray(0);

        // 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;
}

// 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);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}