triangle.cpp

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

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

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

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

const char* fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
"	FragColor = vec4(1.0, 0.5, 0.2, 1.0);\n"
"}\n\0";


int main() {
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	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);
	// resize viewport when glfw window size changes
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
	// load all openGL function pointers
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}
	// vertex shader
	unsigned 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 << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
	}

	// fragment shader
	unsigned 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 << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	// link shaders
	unsigned int shaderProgram = glCreateProgram();
	glAttachShader(shaderProgram, vertexShader);
	glAttachShader(shaderProgram, fragmentShader);
	glLinkProgram(shaderProgram);
	// check 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;
	}
	// after linking, shader objects can be deleted
	glDeleteShader(vertexShader);
	glDeleteShader(fragmentShader);

	//float 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
	//};
	float vertices[] = {
		-0.6f, 0.2f, 0.0f,
		-0.6f, -0.2f, 0.0f,
		0.0f, 0.2f, 0.0f,
		0.0f, -0.2f, 0.0f,
		0.6f, 0.2f, 0.0f,
		0.6f, -0.2f, 0.0f
	};

	// indexed drawing -> reduce duplicated vertices
	//unsigned int indices[] = {
	//	0, 1, 3, // first triangle
	//	1, 2, 3  // second triangle
	//};

	unsigned int indices[] = {
		0, 1, 2,
		1, 2, 3,
		2, 3, 4,
		3, 4, 5
	};

	// Ids for: Vertex Buffer Object, Vertex Array Object, Element Buffer Object
	unsigned int VBO, VAO, EBO;
	glGenVertexArrays(1, &VAO);
	glGenBuffers(1, &VBO);
	glGenBuffers(1, &EBO);
	// subsequent vertex attribute calls are stored inside VAO
	glBindVertexArray(VAO);

	// copy vertices array in a buffer for OpenGL to use
	glBindBuffer(GL_ARRAY_BUFFER, VBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
	glEnableVertexAttribArray(0);

	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindVertexArray(0);

	glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

	while (!glfwWindowShouldClose(window)) {
		processInput(window);
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		glUseProgram(shaderProgram);
		glBindVertexArray(VAO);
		glDrawElements(GL_TRIANGLES, sizeof(indices) / sizeof(unsigned int), GL_UNSIGNED_INT, 0);

		glfwSwapBuffers(window);
		glfwPollEvents();
	}
	// deallocate resources
	glDeleteVertexArrays(1, &VAO);
	glDeleteBuffers(1, &VBO);
	glDeleteBuffers(1, &EBO);
	glDeleteProgram(shaderProgram);


	glfwTerminate();
	return 0;
}

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

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