GL = graphics library

OpenGL started in 1992 to replace proprietary SGI "IRIS GL".

Sub-libraries:

GLU	GL Utilities	Basic objects, textures, some transformations
GLUT	GL Utility Toolkit	Set up windows and handle events. No longer used.
GLEW	GL Extension Wrangler	Maps OpenGL API functions to internal implementation
GLFW	Graphics Library Framework	Windows and events. Good.
GLAD		Maps API functions to implementations. Good.
GLM	GL math	Lots of graphics-oriented math functions. Somewhat messy.

Main graphics loop:

Events can be:

• key press or release
• mouse button press or release
• mouse drag (with button down)
• window resize
• ... many others ...

Each event is processed by a 'handler', which is just a function.

Each event handler is registered during initialization with (in our case) GLFW.

OpenGL usually has two drawing buffers:

One shows what's on the screen (the "front buffer").

The other is used to draw the next image (the "back buffer").

Once drawing in the back buffer is finished, the buffers are swapped so that the new image appears on the screen all at once, rather than bit-by-bit as it was being drawn.

See 00-intro/src/demo1.cpp in openGL.zip

Object vertices are stored in a "vertex buffer object" or VBO.

Each vertex can have many attributes, such as

• position (2D or 3D)
• normal (typically 3D)
• colour (typically RGB)
• texture coordinate (2D or 3D)
• ... etc ...

The VBO is just a buffer and could be set out like this:

In OpenGL, you must:

1. Fill the VBO.
2. Tell OpenGL about the VBO format, including vertex attributes.

See 00-intro/src/demo2.cpp in openGL.zip

Maintain a "world state" that contains all the information necessary to provide a snapshot of the world at a particular instant.

For example, if the world consists of a rotating square, the world state would contain the square's:

• position
• angle
• size

To animate, update the state as a function of either (a) the relative time since the last update or (b) the absolute current time.

See 00-intro/src/demo3.cpp in openGL.zip