OpenGL Graphics Rendering API Basics

Study Notes

OpenGL Basics

OpenGL is a graphics rendering API that allows creating high-quality color images composed of geometric and image primitives.
It is window system independent and operating system independent.

OpenGL as a Renderer

OpenGL draws geometric primitives such as points, lines, and polygons.
It also draws image primitives such as images and bitmaps.
It changes the state of how it draws, including colors, materials, light sources, etc.

Headers and Libraries

OpenGL includes three header files: gl.h, glu.h, and glx.h.
However, glut.h includes all three, so including all three files is redundant.
There are four libraries in an OpenGL program:
- Core OpenGL (GL)
- OpenGL Utility Library (GLU)
- OpenGL Utilities Toolkit (GLUT)
- Other libraries (not specified)

Core OpenGL (GL)

Consists of hundreds of commands, which begin with a prefix "gl".
Models an object via a set of geometric primitives.

OpenGL Utility Library (GLU)

Built on top of the core OpenGL to provide important utilities.
Provides commands for setting camera view and projection, and more.
GLU commands start with a prefix "glu".

OpenGL Utilities Toolkit (GLUT)

Needed to interact with the operating system (e.g., creating a window, handling key and mouse inputs).
Provides more building functions.
GLUT commands start with a prefix "glut".

GLUT Callback Functions

A routine to call when something happens (e.g., window resize, user input, animation).
Register callbacks with GLUT using functions such as glutDisplayFunc, glutIdleFunc, and glutKeyboardFunc.

OpenGL Command Syntax

OpenGL commands use the prefix "gl" and initial capital letters for each word.
Defined constants begin with "GL_" and use all capital letters and underscores to separate words.

Geometric Primitives

In OpenGL, an object is made up of geometric primitives such as triangles, quads, line segments, and points.
A primitive is made up of one or more vertices.
OpenGL supports various primitives, including points, lines, and polygons.

State Machine

OpenGL operates as a state machine, maintaining a set of state variables (e.g., foreground color, background color).
Once a state variable is set, it persists until a new value is given.
Examples include setting the clearing color and foreground color.

Color and Transparency

Color is typically specified in float in the range 0.0f and 1.0f.
Color can be specified using RGB (Red-Green-Blue) or RGBA (Red-Green-Blue-Alpha) components.
The 'A' (or alpha) specifies the transparency (or opacity) index, with 1 being opaque and 0 being totally transparent.
Examples include setting the background color using glClearColor and setting the foreground color using glColor.

Description

Learn about OpenGL (Open Graphics Library) which allows creating high-quality color images with geometric and image primitives. Understand how to use OpenGL as a Renderer to draw geometric and image primitives, change the state of drawing, and work with header files like gl.h, glu.h, and glx.h.