Cube.cpp

#include "Cube.h"

Cube::Cube(float size) 
{
	// Model matrix. Since the original size of the cube is 2, in order to
	// have a cube of some size, we need to scale the cube by size / 2.
	model = glm::scale(glm::vec3(size / 2.f)); 

	// The color of the cube. Try setting it to something else!
     color = glm::vec3(1.0f, 0.95f, 0.1f);
	/*
	 * Cube indices used below.
	 *    4----7
     *   /|   /|
     *  0-+--3 |
     *  | 5--+-6
     *  |/   |/
     *  1----2
	 *
	 */

	// The 8 vertices of a cube.
	std::vector<glm::vec3> vertices
	{
		glm::vec3(-1, 1, 1),
		glm::vec3(-1, -1, 1),
		glm::vec3(1, -1, 1),
		glm::vec3(1, 1, 1),
		glm::vec3(-1, 1, -1),
		glm::vec3(-1, -1, -1),
		glm::vec3(1, -1, -1),
		glm::vec3(1, 1, -1)
	}; 

	// Each ivec3(v1, v2, v3) define a triangle consists of vertices v1, v2 
	// and v3 in counter-clockwise order.
	std::vector<glm::ivec3> indices
	{
		// Front face.
		glm::ivec3(0, 1, 2),
		glm::ivec3(2, 3, 0),
		// Back face.
		glm::ivec3(7, 6, 5),
		glm::ivec3(5, 4, 7),
		// Right face.
		glm::ivec3(3, 2, 6),
		glm::ivec3(6, 7, 3),
		// Left face.
		glm::ivec3(4, 5, 1),
		glm::ivec3(1, 0, 4),
		// Top face.
		glm::ivec3(4, 0, 3),
		glm::ivec3(3, 7, 4),
		// Bottom face.
		glm::ivec3(1, 5, 6),
		glm::ivec3(6, 2, 1),
	}; 

	// Generate a vertex array (VAO) and two vertex buffer objects (VBO).
	glGenVertexArrays(1, &vao);
	glGenBuffers(2, vbos);

	// Bind to the VAO.
	glBindVertexArray(vao);

	// Bind to the first VBO. We will use it to store the vertices.
	glBindBuffer(GL_ARRAY_BUFFER, vbos[0]);
	// Pass in the data.
	glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec3) * vertices.size(), 
		vertices.data(), GL_STATIC_DRAW);
	// Enable vertex attribute 0. 
	// We will be able to access vertices through it.
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), 0);

	// Bind to the second VBO. We will use it to store the indices.
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbos[1]);
	// Pass in the data.
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(glm::ivec3) * indices.size(), 
		indices.data(), GL_STATIC_DRAW);

	// Unbind from the VBOs.
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	// Unbind from the VAO.
	glBindVertexArray(0);
}

Cube::~Cube()
{
	// Delete the VBOs and the VAO.
	glDeleteBuffers(2, vbos);
	glDeleteVertexArrays(1, &vao);
}

void Cube::draw()
{
	// Bind to the VAO.
	glBindVertexArray(vao);
	// Draw triangles using the indices in the second VBO, which is an 
	// elemnt array buffer.
	glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_INT, 0);
	// Unbind from the VAO.
	glBindVertexArray(0);
}

void Cube::update()
{
	// Spin the cube by 1 degree.
	spin(0.1f);
}

void Cube::spin(float deg)
{
	// Update the model matrix by multiplying a rotation matrix
	model = glm::rotate(model, glm::radians(deg), glm::vec3(0.0f, 1.0f, 0.0f));
}