Vertex

• vertex data is a collection of vertices
• a vertex is a collection of data per 3D coordinate
• vertex's data is represented using vertex attributes that can contain any data we'd like (i.e. 3D position, colour)

Vertex Input

• OpenGL is a 3D graphics library so all coordinates that we specify in OpenGL are in 3D (x, y and z coordinate), which are in a specific range between 1.0 and 1.0

  → NDC (Normalized Device Coordinates)

  Once your vertex coordinates have been processed in the vertex shader, they should be in NDC which is a small space where the x, y and z values vary from -1.0 to 1.0. Any coordinates that fall outside this range will be discarded/clipped and won't be visible on your screen.

• vertex input of a single triangle

float vertices[] = {
    -0.5f, -0.5f, 0.0f,
     0.5f, -0.5f, 0.0f,
     0.0f,  0.5f, 0.0f
};

The triangle specified in the code clip above within NDC

<aside> 💡 OpenGL Vertex Coordinate System: [-1, +1]

</aside>

• vertex buffer objects(VBO) store a large number of vertices in the GPU’s memory
  • sending data from CPU to GPU is slow, so we want to send as much as possible at once
  • once the data is in the graphics card's memory the vertex shader has almost instant access to the vertices making it extremely fast

Set Up Vertex Buffer

unsigned int VBO;

// 0. Generate a buffer with a buffer ID & stores into `VBO`
glGenBuffers(1, &VBO);

// 1. Bind the newly created buffer `VBO` to the GL_ARRAY_BUFFER target
//     1. buffer type of vertex buffer object -> GL_ARRAY_BUFFER
//     2. from this point on any buffer calls we make (on GL_ARRAY_BUFFER target)
//          will be used to configure the currently bound buffer
//     3. we can bind to several buffers at once as long as they have a different buffer type
glBindBuffer(GL_ARRAY_BUFFER, VBO);

// 2. Copy the previously defined `vertices` data into currently bound buffer's memory
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

// 3. Set the vertex attributes pointers
glVertexAttribPointer(attribIdx, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);  

// 4. use our shader program when we want to render an object
glUseProgram(shaderProgram);

glBufferData function specifically targeted to copy user-defined data into the currently bound buffer