Video Game Design Composition, 1st Edition Page 324 (324 of 448)

324
Video Game Design Composition
Rotation
Rotation
is circular movement about a central point. In video games,
rotation occurs around the X axis, Y axis or Z axis of the object.
A good example of rotation can be seen in the movement of an airplane.
In a right-hand turn, the right wing rotates down and the left wing rotates
up, as shown in Figure 11-3. This
rotation is about the long central
axis of the plane, which can be
thought of as the X axis. To make
the airplane go up or down, the
pilot controls the pitch. When
taking off, the airplane nose is
rotated up and the tail is rotated
down. This rotation is about an
axis running from wingtip to
wingtip, which can be thought of
as the Y axis. The yaw controls
for the pilot come from the rudder
input. When the airplane turns to
the left with the rudder input, the
nose rotates to the left and the tail
rotates to the right. This rotation is
about a vertical axis, which can be
thought of as the Z axis.
Figure 11-2.
Translation is moving
an object from one
point to another.
Here, the ball is
translated from
(0,0,0) to (5,0,0).
Goodheart-Willcox Publisher
Figure 11-3.
When a plane turns, its wings rotate
about an axis.
Nata-Lia/Shutterstock.com

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324
Video Game Design Composition
Rotation
Rotation
is circular movement about a central point. In video games,
rotation occurs around the X axis, Y axis or Z axis of the object.
A good example of rotation can be seen in the movement of an airplane.
In a right-hand turn, the right wing rotates down and the left wing rotates
up, as shown in Figure 11-3. This
rotation is about the long central
axis of the plane, which can be
thought of as the X axis. To make
the airplane go up or down, the
pilot controls the pitch. When
taking off, the airplane nose is
rotated up and the tail is rotated
down. This rotation is about an
axis running from wingtip to
wingtip, which can be thought of
as the Y axis. The yaw controls
for the pilot come from the rudder
input. When the airplane turns to
the left with the rudder input, the
nose rotates to the left and the tail
rotates to the right. This rotation is
about a vertical axis, which can be
thought of as the Z axis.
Figure 11-2.
Translation is moving
an object from one
point to another.
Here, the ball is
translated from
(0,0,0) to (5,0,0).
Goodheart-Willcox Publisher
Figure 11-3.
When a plane turns, its wings rotate
about an axis.
Nata-Lia/Shutterstock.com

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325
Chapter 11 Animation Composition
Articulation
Articulation
is the bending and positioning of movable parts, such as arms
and legs in synchronization with the translation of a walking character. The legs
articulate in a stepping motion as the character is translated to a new position.
If the legs are articulated without translating the character, the active animation
would look as if the character is running in place.
Articulation is plotted by mapping a point on an object and following it
through the motion path, or animation arc. An
animation arc
is the path an
articulated feature follows through the animation. This is shown in Figure 11-4.
Video game designers need to be aware of the animation arc. How many games
have you played where a character’s arm or leg moves through another object
when it is articulated? This is an error and reflects poorly on the game.
In video game design, an artist often must duplicate the articulation of real
objects or humans. A 3D modeling animator might use a motion-capture system
to record the actual articulation movements of a person. Motion capture is
discussed later in this chapter.
Morphing
Morphing
is a change in the physical shape of an object. Objects can be
squashed, stretched, exploded, joined, and more. Each time the size or shape of the
object changes, a morph occurs. Objects that collide impart energy to each other
when they hit. This energy causes waves or deformations. Additionally, objects can
change state. Water can boil into a gas and metal can be melted into a liquid.
The law of conservation of energy states that energy cannot be created or
destroyed, but can change state. Kinetic energy is the energy of movement.
The kinetic energy of two items colliding cannot be destroyed. Rather it is
transformed into heat, sound, and stored energy. Stored energy is potential
energy. Potential energy can exist as gravitational, elastic, chemical, electrical,
or magnetic energy, as described in Figure 11-5.
Figure 11-4.
The animation arc is
the path an object
follows through an
animation.
Goodheart-Willcox Publisher
Animation
arc

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323
Chapter 11 Animation Composition
the perception is that the book is not moving. This is because you are seeing it
relative to your own frame of reference. You, the car, and the book are traveling at
the same speed. If you held up the book, a person on the side of the road would
see the book moving even though the book is not moving from your perspective.
In video games, perception is determined by the camera. In a side-scrolling
2D game, the camera is looking at objects from the side. Motion is perceived as
left, right, up, and down. In a top-down 2D game, the camera location is above
the game looking down. In this view, motion is perceived as North, South,
East, and West. In a first-person shooter (FPS) game, the entire game map
moves with each step of the player character. Motion is perceived as all objects
moving while the player remains still. The player’s view remains centered on
the screen.
Translation
The most basic of all movement types is translation motion.
Translation
is the movement from one point to another. This is simple right-left, up-
down, and in-out movement. If a ball is located in the Cartesian coordinate
system at the coordinate (0,0,0) and it is translated to coordinate (5,0,0),
the ball has moved five units from the origin on the X axis. This is shown in
Figure 11-2.
Translation is very important in video game design. Each object on the
screen is plotted using the coordinate system. A collision occurs when two
objects have the same coordinates. Game designers must create collision
detection for all of the interactive objects in the scene.
Figure 11-1.
Thank You/Shutterstock.com
A car has a positive acceleration vector when it is speeding up.
Positive Acceleration Vector
Velocity Vector
Negative Acceleration Vector
Velocity Vector

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