OpenGL Graphics Rendering API Basics

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.

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.