Computer Graphics Soft Body Animation - Skinning CO2409 Computer Graphics Week 22.
Computer Graphics Chapter 12 Computer Animation.
-
Upload
isaac-peters -
Category
Documents
-
view
257 -
download
1
description
Transcript of Computer Graphics Chapter 12 Computer Animation.
Computer Graphics Chapter 12Computer Animation LET US ENTER INTO
THE MAGICAL WORLD OF ANIMATION Contents INTRODUCTION APPLICATIONS
DESIGN OF ANIMATION SEQUENCES
GENERAL COMPUTER ANIMATION FUNCTIONS RASTER ANIMATIONS COMPUTER
ANIMATION LANGUAGES KEY FRAME SYSTEMS MOTION SPECIFICATIONS
Computer Animation What is Animation? What is Simulation?
Make objects change over time according to scripted actions What is
Simulation? Predict how objects change over time according to
physical laws Introduction Computer animation is the process used
for generatinganimated images (moving images) using computer
graphics. Animatorsare artists who specialize in the creation of
animation. FromLatinanimti, "the act of bringing to life";
fromanim("to animate" or "give life to") and-ti("the act of"). 2D
ANIMATION 3D ANIMATION APPLICATIONS Video games cartoon Mobile
phones Design Of Animation Sequences
Steps for designing animation sequences. Storyboard Layout Object
definitions Key frame specifications Generation of in-between
frames Storyboard Layout Object Definitions Key frame
Specifications In-between frames GENERAL COMPUTER ANIMATION
FUNCTIONS
Animation software provide basic functions to create animation and
process the individual object. Manipulate data object database.
FUNCTIONS Motion generation. Object rendering. Amorphium Art of
illusion Raster Animations Real-time animations can be generated
using raster operations. ORGANISATION OF A VIDEO COLOUR TABLE
1 41H 65 255 1 Monitor 24-bit 65 Pixel value Red Green Blue
Computer Animation Languages
GENERAL PURPOSE LANGUAGES: C,C++,Pascal, or Lisp(control animation
sequences). SPECIALIZED ANIMATION LANGUAGES
Key frame systems Parameterized systems Scripting systems Key frame
Systems Motion Specifications
Various ways in which motions of objects ca be specified as: Direct
Motion Specification. Goal-Directed Systems. Kinematics and
Dynamics. Direct Motion Specification Goal Directed System
Kinematics and Dynamics
Motion parameters such as position , velocity andacceleration are
specified without reference to the forces. INVERSE KINEMATICS:
Initial and final positions of objects atspecified times and from
that motion parameters . DYNAMICS: The forces that produce the
velocities and accelerations are specified(physically based
modeling). It uses laws such as Newtons laws of motion , Euler or
Navier -stokes equations. Outline Principles of Animation Keyframe
Animation Articulated Figures Principle of Traditional
Animation
Squash and Stretch Slow In and Out Anticipation Exaggeration Follow
Through and Overlapping Action Timing Staging Straight Ahead Action
and Pose-to-Pose Action Arcs Secondary Action Appeal Squash and
Stretch Stretch Squash Slow In and Out Anticipation Computer
Animation Animation Pipeline 3D modeling Motion specification
Motion simulation Shading, lighting, & rendering Postprocessing
Outline Principles of Animation Keyframe Animation Articulated
Figures Keyframe Animation Define Character Poses at Specific Time
Steps Called Keyframes Keyframe Animation Interpolate Variables
Describing Keyframes to Determine Poses for Character in between
Inbetweening Linear Interpolation Usually not enough continuity
Inbetweening Spline Interpolation Maybe good enough Inbetweening
Spline Interpolation Maybe good enough
May not follow physical laws Inbetweening Spline Interpolation
Maybe good enough
May not follow physical laws Inbetweening Inverse Kinematics or
Dynamics Outline Principles of Animation Keyframe Animation
Articulated Figures Articulated Figures Character Poses Described
by Set of Rigid Bodies Connected by Joints Base Arm Hand Scene
Graph Articulated Figures Well-Suited for Humanoid Characters
Articulated Figures Joints Provide Handles for Moving Articulated
Figure Inbetweening Compute Joint Angles between Keyframes Right
Wrong
consider the length constancy Right Wrong Example: Walk Cycle
Articulated Figure: Hip Upper Leg (Hip Rotate)
Knee Lower Leg (Knee Rotate) Hip Rotate + Knee Rotate Lower Leg
Ankle Foot (Ankle Rotate) Foot Example: Walk Cycle Hip Joint
Orientation: Example: Walk Cycle Knee Joint Orientation: Example:
Walk Cycle Ankle Joint Orientation: Challenge of Animation
Temporal Aliasing Motion blur Temporal Ailasing Artifacts due to
Limited Temporal Resolution
Strobing Flickering Temporal Ailasing Artifacts due to Limited
Temporal Resolution
Strobing Flickering Temporal Ailasing Artifacts due to Limited
Temporal Resolution
Strobing Flickering Temporal Ailasing Artifacts due to Limited
Temporal Resolution
Strobing Flickering Motion Blur Composite Weighted Images of
Adjacent Frames
Remove parts of signal under-sampled in time Summary Animation
Requires ... Scripting Inbetweening
Modeling Scripting Inbetweening Lighting, shading Rendering Image
processing Overview Kinematics Dynamics Consider only motion
Determined by positions, velocities, accelerations Dynamics
Consider underlying forces Compute motion from initial conditions
and physics Example: 2-Link Structure
Two Links Connected by Rotational Joints End-Effector X=(x, y) (0,
0) X=(l1cosQ1+ l2cos(Q1+Q2), l1sinQ1+ l2sin(Q1+Q2))
Forward Kinematics Animator Specifies Joint Angles: Q1 and Q2
Computer Finds Positions of End-Effector: X X=(x, y) (0, 0)
X=(l1cosQ1+ l2cos(Q1+Q2), l1sinQ1+ l2sin(Q1+Q2)) Forward Kinematics
Joint Motions can be Specified by Spline Curves
X=(x, y) (0, 0) Forward Kinematics Joint Motions can be Specified
by Initial Conditions and Velocities X=(x, y) (0, 0) Example:
2-Link Structure
What If Animator Knows Position of End-Effector End-Effector X=(x,
y) (0, 0) Inverse Kinematics Animator Specifies End-Effector
Positions: X Computer Finds Joint Angles: Q1 and Q2 X=(x, y) (0, 0)
Inverse Kinematics End-Effector Postions can be Specified by Spline
Curves X=(x, y) (0, 0) Inverse Kinematics Problem for More Complex
Structures
System of equations is usually under-defined Multiple solutions
X=(x, y) (0, 0) Three unknowns: Q1, Q2, Q3 Two equations: x, y
Inverse Kinematics Solution for More Complex Structures
Find best solution (e.g., minimize energy in motion) Non-linear
optimization X=(x, y) (0, 0) Summary Forward Kinematics Inverse
Kinematics
Specify conditions (joint angles) Compute positions of
end-effectors Inverse Kinematics Goal-directed motion Specify goal
positions of end effectors Compute conditions required to achieve
goals Inverse kinematics provides easier specification for many
animation tasks, but it is computationally more difficult Overview
Kinematics Dynamics Consider only motion
Determined by positions, velocities, accelerations Dynamics
Consider underlying forces Compute motion from initial conditions
and physics Dynamics Simulation of Physics Insures Realism of
Motion Space Time Constraints
Animator Specifies Constraints What the characters physical
structure is e.g., articulated figure What the character has to do
e.g., jump from here to there within time t What other physical
structures are present e.g., floor to push off and land How the
motion should be performed e.g., minimize energy Space Time
Constraints
Computer Finds the Best Physical Motion Satisfying constraints
Example: Particle with Jet Propulsion x(t) is position of particle
at time t f(t) is force of jet propulsion at time t Particles
equation of motion is: Suppose we want to move from a to b within
t0 to t1 with minimum jet fuel: Space Time Constraints
Discretize Time Steps Space Time Constraints
Solve with Iterative Optimization Methods Space Time
Constraints
Advantages Free animator from having to specify details of
physically realistic motion with spline curves Easy to vary motions
due to new parameters and/or new constraints Challenges Specifying
constraints and objective functions Avoiding local minima during
optimization Space Time Constraints
Adapting Motion Original Jump Heavier Base Space Time
Constraints
Adapting Motion Hurdle Space Time Constraints
Adapting Motion Ski Jump Space Time Constraints
Editing Motion Original Adapted Space Time Constraints
Morphing Motion The female character morphs into a smaller
character during her spine Space Time Constraints
Advantages Free animator from having to specify details of
physically realistic motion with spline curves Easy to vary motions
due to new parameters and/or new constraints Challenges Specifying
constraints and objective functions Avoiding local minima during
optimization Dynamics Other Physical Simulations Rigid bodies Soft
bodies Cloth
Liquids Gases etc. Cloth Hot Gases cgvr.korea.ac.kr Summary
Kinematics Dynamics Forward kinematics
Animator specifies joints (hard) Compute end-effectors (easy)
Inverse kinematics Animator specifies end-effectors (easier) Solve
for joints (harder) Dynamics Space-time constraints Animator
specifies structures & constraints (easiest) Solve for motion
(hardest) Also other physical simulations