OpenGL animation is any scene with moving objects rendered using OpenGL libraries. Basic animation involves moving objects through a scene, while keyframe animation involves incrementally moving a model to a keyframe. Skeleton animation involves creating a bone structure within a model for realistic movement. Frames are rendered in an off-screen buffer for consistent frame rate.
OpenGL® animation is a generic term applied to any scene that contains moving objects within it and is rendered using the OpenGL® libraries. From a programming standpoint, there are several methods that can be used to create an OpenGL® animation. Within a more computer graphics oriented view, an OpenGL® animation can be any animated sequence rendered with OpenGL®, whether the scene was generated within the program’s source code or within a standalone modeling program. There are several types of animations that can be done with OpenGL® and other supporting libraries, but two of the most commonly used are keyframe animation and skeleton animation.
The most basic type of OpenGL® animation simply involves moving an object through a scene. This is usually done by equally changing the position of each of the vertex coordinates, slowly translating them to the desired location. The position of the camera in a scene can also be changed to create an animation effect, although in this case the entire scene will remain static. This basic form of animation is often used in two-dimensional (2D) programs where objects are just placeholders to display textures.
Keyframe animation is a much more complex process. This form of OpenGL® animation involves taking a model that has been loaded into the scene and incrementally moving it to another location, called a keyframe. An example is a model of a waving hand. The hand’s initial position is compared to another animation model, or keyframe, where the hand is fully extended. The average and incremental hand motion creates the animation without the need to memorize the hand’s position in each increment along the way.
Another type of OpenGL® animation is known as skeleton animation. This involves creating a model, usually of an articulated human or animal, and then creating some type of bone structure within the model. Each of the bones is attached, virtually, to the surrounding vertices of the model. Bones exert a certain force, or weight, on each vertex so that when the bone itself is moved, the surrounding model reacts and the mesh that forms the model’s “skin” deforms. This type of animation takes time to create, but can provide very realistic movement when done correctly.
An OpenGL® animation is based both on the model created to be animated and on how a program performs the animation. The most commonly used way is to render the frames of the animation in an off-screen area known as a buffer before being drawn onto the visible screen. This allows the image to be drawn in its entirety without the user having to look at it if it is too slow. Many computer programs that use OpenGL® animation must also ensure that they maintain a consistent frame rate to avoid juddering animation, which is achieved by timing each frame drawn and waiting or speeding up the rendering process.
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