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Tradigital MayaA CG Animator's Guide to Applying the Classic Principles of Animation
By Lee Montgomery
Focal PressCopyright © 2012 Elsevier Inc.
All right reserved.
Chapter OneArcs – Organic Movement/ Natural Motion
Very few living organisms are capable of moves that have a mechanical in and out or up and down precision. The Illusion of Life: Disney Animation – Frank Thomas and Ollie Johnston
In this chapter, we'll be looking at the basis of natural movement – arcs. Arcs are present in the majority of motions in the natural world; this is due to the effects of mass, weight, and inertia on objects, whether living or not. Think of an object traveling through the air, such as a ball being thrown; although the ball may follow a straighter line at the start of the throw, it will naturally follow more of an arc, as it loses speed and gravity takes hold. The natural phenomenon of arced motion needs to be replicated convincingly in animation to add believability, if the motion is not arced or the timing is even, it will look unnatural and the illusion will be lost.
Natural arcs can be seen in the animation exercises throughout this book. The following are some examples where you would see arcs in motion in the other tutorials exercises:
Bat Swing – In the baseball bat swing animation that we'll look at in later chapters, a clear arced motion can be seen on the swing; this is because the bat swings from the wrist, which is a fixed pivot on the hand. This pendulum type motion is typical in human or organic motion and also applies to the limbs on the body (see Fig. 1.0.1, left screens).
Jump Landing – In the jump animation that we'll look at in Chapter 11, there are natural arcs on the body throughout the animation, from the start through the motion in the air and on the landing. At the landing phase of the sequence, the body pivots around the foot that's planted on the ground, with natural arcs visible on the hips and torso (see Fig. 1.0.1, third screen from left).
Character Posing – Organic arcs are also visible in the body's form and shape in real life, even when the body is not in motion. This is due to the curvature of the spine and weight distribution on the body. Typically, the body distributes weight off center, which creates natural arced shapes running across the body (see Fig. 1.0.1, fourth screen from left).
If the body is posed with purely straight lines or blocky square shapes, the pose will look unnatural and robotic. This is something, which is common in many novice animations. Throughout the book, we will look at how to pose the body with natural arcs that give the animation weight and balance. We will look in detail at character posing specifically in Chapter 9.
Arcs in Object Motion
In the first two tutorials in this chapter, we'll look specifically at arced motion for object animation. As in the jump animation example that we touched on, objects moving through the air should have a natural fluid arced motion due to momentum, inertia (or loss of speed), and the effect of gravity.
Ball Bounce – In the first tutorial, we'll look at a ball bounce animation. Arcs are apparent in the motion in both the timing of the animation as the ball's momentum is lost and in the motion as the ball bounces across the ground (see Fig. 1.0.2, left screens).
Plane Trajectory – In the tutorial of Chapter 2, we'll look at a takeoff animation for an F16 fighter plane. Although the F16 fighter is being driven into the air by the rocket jets on the plane, there are still natural arcs that should be apparent on both liftoff (due to momentum and gravity) and flight as the plane maneuvers (see Fig. 1.0.2, right screens).
Localized Arcs – Human Motion
The third and fourth tutorials in this chapter will focus specifically on arcs in human motion. For these exercises, we will look at arcs on a couple of localized areas on the body. These tutorials will introduce common character animation concepts including posing and Inverse Kinematics.
In the arm swing tutorial, we will look at the pendulum swing on the arm; in addition to analyzing the arc on the arm swing, we will also touch on a couple of other principles of animation including follow-through and Ease In & Ease Out to mimic real-world motion through animation (see Fig. 1.0.3, left).
In the run cycle tutorial, we will look specifically at the arc on the hip trajectory in the animation. The natural arc of the hips during the weight shifts and foot plants on the run is key in creating believability in the run cycle (see Fig. 1.0.3, right).
Chapter 1.1 – Animation Test – Bouncing Ball
The bouncing ball animation test was originally used at Disney as a test of skill for new animators joining the studio. The test is still in use today at studios including Pixar:
no matter how seasoned you are, this is the first thing that an animator would do when they come into Pixar, because it shows timing, spacing, squash and stretch, anticipation, etc. Andrew Cordon, Senior Animator, Pixar – 3D World Issue 130, June 2010, p. 24.
In this tutorial, we'll be focusing initially on creating fluid blocked in movement for the ball bounce through the standard manipulation and handkeying tools in Maya. The tutorial will first introduce you to the fundamentals of creating and editing animation in Maya including the following: Animation Preferences, the Channel Box (for viewing motion values) Transformation tools for manipulation, keyframing, and playback controls (see Fig. 1.1.01).
Other key animation principles including Ease In & Ease Out, Squash and Stretch, and Timing & Spacing will also be introduced with the use of key edits using the Time Slider, Channel Box, and Maya Graph Editor to edit motion timing. The Maya Motion Trail feature will also be utilized alongside display ghosting to validate the final arc on the ball bounce as well as the timing intervals (see Fig. 1.1.02).
For our animation of the bouncing ball, we'll work on an initial bounce cycle that can be looped. For a ball bouncing, this would be less than 1 second, with the time varying based on the height of the bounce and mass of the ball.
For the length of the animation sequence and playback rate, this can be set from Maya's animation preferences. Let's take a look at how to set up animation and playback range within Maya:
Open a new session of Maya or select File > New Scene to clear the current scene.
The preferences for Maya's frame range can be set from a few different places:
Animation Preferences button – This is at the bottom right corner of the user interface; it is the small white icon with figure in red beside the key icon (see Fig. 1.1.1, top left screenshot). Clicking the "Animation Preferences" button will automatically open Maya's "Preferences" window to display the "Time Slider" options (see Fig. 1.1.1, middle screenshot).
Window > Settings/Preferences > Preferences (see Fig. 1.1.1, bottom left screenshot) – Selecting this option (from Window menu at the top of the UI) will open the Maya Preferences window; from here, select the "Time Slider" category from the left pane (see Fig. 1.1.1, middle screenshot).
In the Preferences window, under the "Time Slider" section, set the animation and playback range to 20 frames, which is just less than 1 second at 24 frames per second (fps):
Playback start/end = 1/20.
Animation start/end = 1/20.
The "Playback" and "Animation start/end" can also be set interactively from the input fields underneath the "Time Slider" in Maya (see Fig. 1.1.1, right screenshots). The gray box between the input fields can also be dragged left and right to increase or decrease the playback range.
In the Preferences window, under the "Playback" section, set the following:
Playback Speed: = real time [24 fps].
Setting playback to real time will force Maya to attempt to maintain a constant playback rate of 24 fps. This setting is critical in evaluating the animation in real time in the Viewport.
Maya Grid Display
For the ball bounce, we'll be working on animating the ball bouncing across the scene. While working, it is useful to have the Grid display in Maya setup appropriately for the scene to preview the animation. As we'll be animating the ball traveling a fair distance across the ground plane, let us set up the grid, so that it is larger and extends across more of the Viewport:
From the top of the user interface, select the Display menu and select:
Display > Grid Options.
To select options within Maya from any of the menus, click the small square-shaped icon at the right of the menu item (see Fig. 1.1.2, top left screenshot).
The "Grid Options" window will open (see Fig. 1.1.2, bottom left screenshot). From here, the display of the Grid in the Viewport can be customized. Set the following: Size > Length and width = 40.00 units (see Fig. 1.1.2, bottom left screenshot).
Hit "Apply and Close" at the bottom of the window to apply the change and close the dialog window. The size of the Grid displayed in the scene view will be larger (see Fig. 1.1.2, middle screenshot).
The background color in the Maya Viewport can be toggled from the default blue color to gray/black with the following shortcut key:
Alt + B = Viewport background color.
The Grid display can be toggled on/off from either of the following:
The Viewport panel icons at the top of the panel window. Toggle on/off the Grid icon (see Fig. 1.1.2, top right screenshot).
The "Show" menu from the panel drop-down menus above the panel. Toggle on/off "Grid" from here (see Fig. 1.1.2, bottom right screenshot).
Creating the Bouncing Ball
We'll use a primitive NURBS sphere for the bouncing ball animation.
From the top row of menus at the top of the Maya User Interface, select the "Create" menu and select:
Create > NURBS Primitives > Sphere.
This will activate the create tool, click and drag near to the origin of the scene (intersection of the grid) to create a new NURBS sphere (see Fig. 1.1.3, left screenshot).
The Maya Channel Box
Maya's Channel Box can be used to set the position of the ball and scaling:
With the NURBS sphere still selected, toggle on display of the Maya Channel Box with Ctrl + A shortcut toggle (see Fig. 1.1.3, second screenshot from left).
The Channel Box displays the following by default:
Name of the selected object listed at top – "nurbsSphere1".
Transform channels – Translate/Rotate and Scale X/Y/Z.
The values shown here correlate with the position (Translate X/Y/Z), rotation (Rotate X/Y/Z), and scaling (Scale X/Y/Z) of the object (or node) in the scene view (or Viewport), and the values update automatically when the object is transformed in the Viewport.
The Channel Box can be used to numerically position, rotate, or scale objects in the scene:
With the sphere selected, click with the left mouse button in the first numeric input field in the Channel Box for "Translate X". With the left mouse button still pressed down, drag downward to the "Rotate Z" numeric input field for the object and then release the left mouse button.
The selected channel input fields will be highlighted in blue to show that they are selected. The last selected input field (Rotate Z) will show the number selected and highlighted.
From the numeric keypad on your computer, hit 0 and Enter – this will set all of the selected attributes in the Channel Box to value = 0 (see Fig. 1.1.3, second screenshot from left). The sphere will be positioned at the global origin (Translate X/Y/Z = 0.0).
At the bottom of the Channel Box is a heading titled "INPUTS"; this is the input attributes for the sphere.
Under INPUTS, click on "makeNurbSphere1" to display the input attributes and double-click in the "Radius" section and type 2.4 to set the Sphere's radius to 2.4 units (see Fig. 1.1.3, second screenshot from left).
Shading in the viewport panel can be toggled between Wireframe and Shaded display from either the shading toggle buttons at the top of the panel, the Shading menu at the top of the panel, or shortcut keys 4 (wireframe) or 5 (shaded) (see Fig 1.1.3, right screens).
Excerpted from Tradigital Maya by Lee Montgomery Copyright © 2012 by Elsevier Inc.. Excerpted by permission of Focal Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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