Implementation:Vertex Buffer

Overview

In this post we shall deep dive and understand mechanics behind sending vertex data to the GPU. Vertex data is obtained from mesh objects such as cubemesh which will be discussed later. The vertex data consists of Position, Color, Normal, and Texture Coordinate of each vertex. They are basically stored into VBO, EBO buffers. Later they are packaged into VAO objects.

Below are some of the OpenGL related terminologies used commonly when vertex data of 3D objects is passed to the pipeline especially vertex shader to render them on screen. Don't get bogged down with its details. It will become clear as we go.

Vertex Buffer Object(VBO)

A vertex buffer object (VBO) is an OpenGL feature that provides methods for uploading vertex data (Position, Color, Normal, Texture Coordinates). A single VBO can store one or more of these data. However in this implementation one buffer is used for one type of data.

 

Element Buffer Object(EBO)

To optimize data transfer, EBO stores indices of the vertices specifically, and OpenGL calls the indices of these vertices to determine which vertices should be drawn.

Vertex Array Object(VAO)

VAO can be considered as a collection of EBO and VBOs. VAO store buffer names for each VBO and EBO, as well as how the vertices are laid out in the vertex buffers. The vertex id associated with VAO maps to location defined in the vertex shader.

The following diagram depicts the relationships between VAO and VBO.

Details

VertexData

The VertexData class is template based and it stores VBO and EBO data and manages their lifetime in the Applications memory space. 

The details are described below.

Constructor

Initializes the gl enumeration type and its size.

Members

Name	Description
id	Identifies the unique id assigned to the buffer.
data	Contains raw data as vector.
valtype valsize	valtype gl enumeration of the datype. valsize size of the individual element.

Methods

Name	Description
add	Adds a new element to the vector data
itemsize	Returns the size of template type T or the element type stored in the vector data
datasize	Returns the total size of all the elements in the vector data
cleanup	Releases opengl buffers.
bindEBO	Binds EBO buffers
bindEnableVBO	Binds VBO buffers and enables them.

VAOUtil 

VAOUtil class defines a  VAO and its associated VBOs and EBO discussed in the previous post. 

The VertexData class is template based and it stores VBO and EBO data and manages their lifetime. VAOUtil class defines VertexData class for Position, Color, Normal, Texture Coordinates.

Members

Name	Description
id	Identifies the unique id assigned to the VAO object.
positions colors normals texcrds	Contains vertex data for VBO buffers
indices	Contains positional data for EBO buffers

Methods

Name	Description
AddColor	Adds a new element to the vector colors
AddPosition	Adds a new element to the vector positions
AddNormal	Adds a new element to the vector normals
AddTexCord	Adds a new element to the vector texcrds
AddIndex	Adds a new element to the vector indices
bindVAO	Binds VAO for drawing
unbindVAO	Unbinds VAO after drawing
cleanup	Releases all Vertex Arrays and clears VBO and EBO data.
SetupEBO	Binds EBO buffers
SetupVBO	Binds VBO buffers and enables them.