/Draw a single tri-angle

#include "GL/glew.h"
#include "GLFW/glfw3.h"
#include <iostream>
using namespace std;
#define numVAOs 1
GLuint renderingProgram;
GLuint vao[numVAOs];

GLuint createShaderProgram() {
	const char* vshaderSource =
		"#version 430 \n"
		"void main(void)\n"
		"{if (gl_VertexID == 0) gl_Position = vec4(0.25, -0.25, 0.0, 1.0);\n"
		"else if (gl_VertexID == 1) gl_Position = vec4(-0.25, -0.25,0.0,1.0);\n"
		"else gl_Position = vec4(0.25, 0.25, 0.0, 1.0);}\n";
	
	const char* fshaderSource =
		"#version 430 \n"
		"out vec4 color; \n"
		"void main(void) \n"
		"{ color = vec4(0.5, 0.0, 1.0, 1.0); }";

	GLuint vShader = glCreateShader(GL_VERTEX_SHADER);
	GLuint fShader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(vShader, 1, &vshaderSource, NULL);
	glShaderSource(fShader, 1, &fshaderSource, NULL);
	glCompileShader(vShader);
	glCompileShader(fShader);
	GLuint vfProgram = glCreateProgram();
	glAttachShader(vfProgram, vShader);
	glAttachShader(vfProgram, fShader);
	glLinkProgram(vfProgram);
	return vfProgram;
}

void init(GLFWwindow* window) {
	renderingProgram = createShaderProgram();
	glGenVertexArrays(numVAOs, vao);
	glBindVertexArray(vao[0]);
}
void display(GLFWwindow* window, double currentTime) {
	//glClearColor(1.0, 0.0, 0.0, 1.0);
	//glClear(GL_COLOR_BUFFER_BIT);
	glUseProgram(renderingProgram);
	glPointSize(30.0f);
	glDrawArrays(GL_TRIANGLES, 0, 3);  //three vertices of triangle primitive
}
int main(void) {
	if (!glfwInit()) { exit(EXIT_FAILURE); }
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	GLFWwindow* window = glfwCreateWindow(600, 600, "Triangle glfw window", NULL, NULL);
	glfwMakeContextCurrent(window);
	if (glewInit() != GLEW_OK) { exit(EXIT_FAILURE); }
	glfwSwapInterval(1);
	init(window);
	while (!glfwWindowShouldClose(window)) {
		display(window, glfwGetTime());
		glfwSwapBuffers(window);
		glfwPollEvents();
	}
	glfwDestroyWindow(window);
	glfwTerminate();
	exit(EXIT_SUCCESS);
}