Animation 2: Computer Animation

Computer Animation

  • This week we will talk about computer animation proper
  • Go over some basic techniques
  • Demo blender
  • Talk about character animation if there is time

Overview and aims

  • This lecture will explain the basic computer animation techniques
  • By the end of the lecture you will be able to:
    • Describe transforming and keyframing in computer animation
    • Create and render a keyframe animation in blender

Computer Animation

  • A lot of computer animation is about saving time and effort
  • Many things can be automated
  • There are also lots of things that are hard to do traditionally (3D)

Computer Animation

  • Computer animation (both 2D and 3D) is quite a lot like Stop Motion Animation
  • You put a lot of effort into creating a (Virtual) model of a character
  • Then when animating it you move it frame by frame

Computer Animation

  • Computer animation (both 2D and 3D) is quite a lot like Stop Motion Animation
  • You put a lot of effort into creating a (Virtual) model of a character
  • Then when animating it you move it frame by frame

Computer Animation

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  • Characters (and all objects) are made out of polygons
  • Normally tirangles or quadrilaterals
  • Called a mesh
  • Can be very complex
  • We rarely aniamted the mesh directly

Controls

  • Most of the time you will be moving things around
  • Use “Transforms”
    • Translation (changing position)
    • Rotation
  • For characters you also get skeletons
  • Your objects can be as complex as you like, the act of moving them is simple

Controls

  • The animation software will automatically draw the frame when you move the character
  • Much, much less hard work than doing it by hand

Keyframing

  • Keyframing can reduce this effort even more
  • The animator only needs to define the “key frames” of a movement
  • The computer does the in betweening
  • Keyframes aren’t images
  • They are poses of a character

Character animation

  • To animate a human character you need to do more than just move them around
  • Control the movement of the parts of the body
  • Animate the character’s skeleton

Skeletal Animation

  • The fundamental aspect of human body motion is the motion of the skeleton
  • The motion of rigid bones linked by rotational joints (first approximation)
  • I will discuss other elements of body motion such as muscle and fat briefly later

Skeletal Animation

  • Circles are rotational joints lines are rigid links (bones)
  • The red circle is the root (position and rotation offset from the origin)
  • The character is animated by rotating joints and moving and rotating the root

Skeletal Animation

Problems with Forward Kinematics

  • Forward kinematics is a simple and powerful system
  • However, it can be fiddly to animate with
  • If you want to make sure that a hand is in contact with an object it can be difficult

Inverse Kinematics

  • Given a desired position for a part of the body (end effector) work out the required joint angles to get it there
  • The computer calculates the joint rotations
  • Simpler to animate with

Motion Capture

  • This motion can be created by an animator in an animation package
  • However, we can also record motion from a real actor performing actions
  • This process is called motion capture
  • Very heavily used in film and computer games
  • Gives very high quality motion

Motion Capture

  • Put markers on the body
  • Track the positions of the marker points

Making it look good

  • A skeleton is a great way of animating a character but it doesn’t necessarily look very realistic when rendered
  • Need to add a graphical “skin” around the character

Segmented Characters

  • Have a separate piece of geometry attached to each joint
  • e.g. a model for the hand and one for the head
  • OK but body is broken up

Smooth Skinning

  • We want to represent a character as a single smooth mesh (a “skin”)
  • This should deform smoothly based on the motion of the skeleton

Smooth Skinning

  • Associate each part of a mesh with one or more joints
  • Each part has a weight for each joint
  • The resulting position is a weighted average of the individual joint transforms

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