How to fill up the side of a cylinder using triangles - c++

Question

I am trying to create six sides for a cylinder using OpenGL and two triangles for each side. I am currently using wireframe mode, so I can see the triangles that are being used. I finished by code for the cylinderVertices array and the cylinderIndices array, but whenever I run the program, the base comes out perfectly, but the sides are messed up. Is there something wrong with the angles that I am using for the sine and cosine coordinates in my cylinderVertices array or do my indices need fixing in my cylinderIndices array? Maybe someone can help me give the right coordinates. Here is my code:
#include <GL\glew.h>
#include <GLFW\glfw3.h>
#include <iostream>
// GLM library
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
using namespace std;
int width, height;
const double PI = 3.14159;
const float toRadians = PI / 180.0f;
// Draw Primitive(s)
void draw() {
GLenum mode = GL_TRIANGLES;
GLsizei indices = 63;
glDrawElements(mode, indices, GL_UNSIGNED_BYTE, nullptr);
}
// Create and Compile Shaders
static GLuint CompileShader(const string& source, GLuint shaderType) {
// Create Shader Object
GLuint shaderID = glCreateShader(shaderType);
const char* src = source.c_str();
// Attach source code to Shader object
glShaderSource(shaderID, 1, &src, nullptr);
// Compile Shader
glCompileShader(shaderID);
// Return ID of Compiled shader
return shaderID;
}
// Create Program Object
static GLuint CreateShaderProgram(const string& vertexShader, const string& fragmentShader) {
// Compile vertex shader
GLuint vertexShaderComp = CompileShader(vertexShader, GL_VERTEX_SHADER);
// Compile fragment shader
GLuint fragmentShaderComp = CompileShader(fragmentShader, GL_FRAGMENT_SHADER);
// Create program object
GLuint shaderProgram = glCreateProgram();
// Attch vertex and fragment shaders to program object
glAttachShader(shaderProgram, vertexShaderComp);
glAttachShader(shaderProgram, fragmentShaderComp);
// Link shaders to create executable
glLinkProgram(shaderProgram);
// Delete compiled vertex and fragment shaders
glDeleteShader(vertexShaderComp);
glDeleteShader(fragmentShaderComp);
// Return Shader Program
return shaderProgram;
}
int main(void) {
width = 640; height = 480;
GLFWwindow* window;
// Initialize the library
if (!glfwInit())
return -1;
// Create a windowed mode window and its OpenGL context
window = glfwCreateWindow(width, height, "Main Window", NULL, NULL);
if (!window) {
glfwTerminate();
return -1;
}
// Make the window's context current
glfwMakeContextCurrent(window);
// Initialize GLEW
if (glewInit() != GLEW_OK)
cout << "Error!" << endl;
GLfloat cylinderVertices[] = {
// Base of the cylinder
// Triangle One // Color
0.0, 0.0, 0.0, 1.0, 0.0, 0.0, // Vertex 0 red
cos( 0 * toRadians), sin( 0 * toRadians), 0.0, 0.0, 1.0, 0.0, // Vertex 1 green
cos( 60 * toRadians), sin( 60 * toRadians), 0.0, 0.0, 0.0, 1.0, // Vertex 2 blue
// Part of Triangle Two
cos(120 * toRadians), sin(120 * toRadians), 0.0, 1.0, 0.0, 1.0, // Vertex 3 purple
// Part of Triangle Three
cos(180 * toRadians), sin(180 * toRadians), 0.0, 0.0, 1.0, 0.0, // Vertex 4 greem
// Part of Triangle Four
cos(240 * toRadians), sin(240 * toRadians), 0.0, 0.0, 0.0, 1.0, // Vertex 5 blue
// Part of Triangle Five
cos(300 * toRadians), sin(300 * toRadians), 0.0, 1.0, 0.0, 1.0, // Vertex 6 purple
// Part of Triangle Six
cos(360 * toRadians), sin(360 * toRadians), 0.0, 0.0, 1.0, 0.0, // Vertex 7 green
// Sides of the cylinder
// Part of Triangle Seven
cos( 0 * toRadians), sin( 0 * toRadians), 2.0, 1.0, 0.0, 0.0, // Vertex 8 red
// Part of Triangle Eight
cos( 45 * toRadians), sin( 45 * toRadians), 2.0, 0.0, 1.0, 0.0, // Vertex 9 green
// Part of Triangle Nine
cos( 60 * toRadians), sin( 60 * toRadians), 2.0, 0.0, 0.0, 1.0, // Vertex 10 blue
// Part of Triangle Ten
cos( 105 * toRadians), sin( 105 * toRadians), 2.0, 1.0, 0.0, 1.0, // Vertex 11 purple
// Part of Triangle Eleven
cos( 120 * toRadians), sin( 120 * toRadians), 2.0, 1.0, 0.0, 0.0, // Vertex 12 red
// Part of Triangle Twelve
cos( 165 * toRadians), sin( 165 * toRadians), 2.0, 0.0, 1.0, 0.0, // Vertex 13 green
// Part of Triangle Thirteen
cos( 180 * toRadians), sin( 180 * toRadians), 2.0, 0.0, 0.0, 1.0, // Vertex 14 blue
// Part of Triangle Fourteen
cos( 225 * toRadians), sin( 225 * toRadians), 2.0, 1,0, 0.0, 1.0, // Vertex 15 purple
// Part of Triangle Fifteen
cos( 240 * toRadians), sin( 240 * toRadians), 2.0, 1.0, 0.0, 0.0 // Vertex 16 red
};
// Define element indices
GLubyte cylinderIndices[] = {
0,1,2,
0,2,3,
0,3,4,
0,4,5,
0,5,6,
0,6,7,
1,2,8,
2,8,9,
3,2,10,
2,9,10,
3,10,11,
3,4,11,
4,11,12,
4,5,12,
5,12,13,
5,6,13,
6,13,14,
5,6,14,
5,6,15,
6,1,15,
1,6,8
};
// Enable Depth Buffer
glEnable(GL_DEPTH_TEST);
// Wireframe mode
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
GLuint VBO, EBO, VAO;
glGenBuffers(1, &VBO); // Create VBO and returns ID
glGenBuffers(1, &EBO); // Create EBO
glGenVertexArrays(1, &VAO); // Create VAO
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO); // Select VBO and activate buffer
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO); // Select EBO
glBufferData(GL_ARRAY_BUFFER, sizeof(cylinderVertices), cylinderVertices, GL_STATIC_DRAW); // Load vertex attributes
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cylinderIndices), cylinderIndices, GL_STATIC_DRAW); // Load indices attributes
// Specify attributes location and layout to GPU
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);
// Color attribute location and layout
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
glEnableVertexAttribArray(1);
glBindVertexArray(0);
// Vertex shader source code
string vertexShaderSource =
"#version 330 core\n"
"layout(location = 0) in vec4 vPosition;"
"layout(location = 1) in vec4 aColor;"
"out vec4 oColor;"
"uniform mat4 model;"
"uniform mat4 view;"
"uniform mat4 projection;"
"void main()\n"
"{\n"
"gl_Position = projection * view * model * vPosition;"
"oColor = aColor;"
"}\n";
// Fragment shader source code
string fragmentShaderSource =
"#version 330 core\n"
"in vec4 oColor;"
"out vec4 fragColor;"
"void main()\n"
"{\n"
"fragColor = oColor;"
"}\n";
// Creating Shader Program
GLuint shaderProgram = CreateShaderProgram(vertexShaderSource, fragmentShaderSource);
while (!glfwWindowShouldClose(window)) {
// Resize window and graphics simultaneously
glfwGetFramebufferSize(window, &width, &height);
glViewport(0, 0, width, height);
// Render here
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Use Shader Program exe and select VAO before drawing
glUseProgram(shaderProgram); // Call Shader per-frame when updating attributes
// Declare identity matrix
glm::mat4 modelMatrix(1.0f);
glm::mat4 viewMatrix(1.0f);
glm::mat4 projectionMatrix(1.0f);
// Initialize transforms
modelMatrix = glm::scale(modelMatrix, glm::vec3(0.5f, 0.5f, 0.5f));
// I increased the third argument from -3.0f to -6.0f to make the object smaller
viewMatrix = glm::translate(viewMatrix, glm::vec3(0.0f, 0.0f, -6.0f));
// I changed up somme of the arguments, so the object would tilt left instead of toward me
viewMatrix = glm::rotate(viewMatrix, 45.0f * toRadians, glm::vec3(-0.5f, 1.0f, 1.5f));
projectionMatrix = glm::perspective(45.0f * toRadians, (GLfloat)width / (GLfloat)height, 0.1f, 100.0f);
// Select uniform shader and variable
GLuint modelLoc = glGetUniformLocation(shaderProgram, "model");
GLuint viewLoc = glGetUniformLocation(shaderProgram, "view");
GLuint projectionLoc = glGetUniformLocation(shaderProgram, "projection");
// Pass transform to Shader
glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(viewMatrix));
glUniformMatrix4fv(projectionLoc, 1, GL_FALSE, glm::value_ptr(projectionMatrix));
glBindVertexArray(VAO); // User-defined VAO must be called before draw
for (GLuint i = 0; i < 4; i++) {
glm::mat4 modelMatrix(1.0f);
glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(modelMatrix));
// Draw primitive(s)
draw();
}
// Unbind Shader exe and VOA after drawing per frame
glBindVertexArray(0); // In case different VAO will be used after
glUseProgram(0); // In case different shader will be used after
glBindVertexArray(VAO);
// Swap front and back buffers
glfwSwapBuffers(window);
// Poll for and process events
glfwPollEvents();
}
glfwTerminate();
return 0;
}

Answer 1

This fixed the problem:
GLfloat cylinderVertices[] = {
// Base of the cylinder
// Triangle One // Color
0.0, 0.0, 0.0, 1.0, 0.0, 0.0, // Vertex 0 red
cos( 0 * toRadians), sin( 0 * toRadians), 0.0, 0.0, 1.0, 0.0, // Vertex 1 green
cos( 60 * toRadians), sin( 60 * toRadians), 0.0, 0.0, 0.0, 1.0, // Vertex 2 blue
// Part of Triangle Two
cos(120 * toRadians), sin(120 * toRadians), 0.0, 1.0, 0.0, 1.0, // Vertex 3 purple
// Part of Triangle Three
cos(180 * toRadians), sin(180 * toRadians), 0.0, 0.0, 1.0, 0.0, // Vertex 4 greem
// Part of Triangle Four
cos(240 * toRadians), sin(240 * toRadians), 0.0, 0.0, 0.0, 1.0, // Vertex 5 blue
// Part of Triangle Five
cos(300 * toRadians), sin(300 * toRadians), 0.0, 1.0, 0.0, 1.0, // Vertex 6 purple
// Part of Triangle Six
cos(360 * toRadians), sin(360 * toRadians), 0.0, 0.0, 1.0, 0.0, // Vertex 7 green
// Sides of the cylinder
// Part of Triangle Seven
cos( 0 * toRadians), sin( 0 * toRadians), 2.0, 1.0, 0.0, 0.0, // Vertex 8 red
// Part of Triangle Eight
cos( 60 * toRadians), sin( 60 * toRadians), 2.0, 0.0, 1.0, 0.0, // Vertex 9 green
// Part of Triangle Nine
cos( 120 * toRadians), sin( 120 * toRadians), 2.0, 0.0, 0.0, 1.0, // Vertex 10 blue
// Part of Triangle Ten
cos( 180 * toRadians), sin( 180 * toRadians), 2.0, 1.0, 0.0, 1.0, // Vertex 11 purple
// Part of Triangle Eleven
cos( 240 * toRadians), sin( 240 * toRadians), 2.0, 1.0, 0.0, 0.0, // Vertex 12 red
// Part of Triangle Twelve
cos( 300 * toRadians), sin( 300 * toRadians), 2.0, 0.0, 1.0, 0.0, // Vertex 13 green
};
// Define element indices
GLubyte cylinderIndices[] = {
// Bottom base
0,1,2,
0,2,3,
0,3,4,
0,4,5,
0,5,6,
0,6,7,
// Sides
1,2,8,
2,9,8,
2,3,9,
3,10,9,
3,4,10,
4,11,10,
5,11,4,
5,12,11,
5,6,12,
6,13,12,
6,1,13,
1,8,13
};