Lec11 Advanced Computer Animation Techniques_2122.pdf

EIE 3101 Computer Animation Lec 11 Advanced Computer Animation Techniques 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 12 2021/22 sem 1 2 Content Ch12 Advanced Computer Animation Techniques Tutorial  Light Animation  B...

EIE 3101 Computer Animation Lec 11 Advanced Computer Animation Techniques 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 12 2021/22 sem 1 2 Content Ch12 Advanced Computer Animation Techniques Tutorial  Light Animation  Biped footsteps walking  MassFX Tools 3 Dynamics Simulations  Dynamics simulation techniques, also called motion dynamics, generate realistic motion of rigid body objects or fluids by simulating their physical properties and the natural laws of physical motion.  Motion dynamics techniques take into account the characteristics of  solids flexibility) (e.g. weight, mass, inertia, and  liquids and gases (e.g. density, cohesion, viscosity, even stickiness)  external forces (e.g. temperature, speed, pressure, friction or gravity)  Collisions with other objects  Dynamics simulations can be combined with other advanced animation techniques such as inverse kinematics and simple keyframe animation. 4 Rigid body dynamics simulation  A rigid body dynamics simulation calculates the motion of objects through time by providing the software with some of the physical properties of an object  Mainly its mass  Some information about the forces applied to the object (Fig 12.3.1)  Mass = density x volume  Forces have a specific strength or intensity, and a direction.  A dynamic simulation calculates the acceleration experienced by an object with a certain mass when a force is applied to it (force = mass x acceleration ).  The motion of objects is calculated by using the effects of acceleration on the object over distance and time to define the velocity and positions of the object through time. 5 6 Fluid dynamics simulation  Fluid dynamics simulation can simulate the motion of non-solid materials such as liquids and gases through time and space, using different pressures and temperatures to visualize changes in density, mass, and viscosity.  Some of the striking stresses and flow effects revealed by fluid dynamics simulations include turbulence with its trademark vortexes and swirling, perturbation, recirculation, compression, expansion, and diffusion.  Fluid dynamics simulations are commonly calculated on particle streams or blobby surfaces.  3dsMax 2018.4 Fluid Presets https://youtu.be/uKraHx9Q19I 7 Dynamic simulation  Dynamic simulations are calculated based on a particular length of real time and then sampled at a specific rate of frames per second.  Ideally the dynamic simulations should be sampled at a minimum of 24-30 frames per second, which is the rate at which film and video are recorded  Dynamic simulations are run by default on all of the elements present in the 3-D environment.  Cameras and lights have to be turned off in the simulation so that they are not affected by it.  Otherwise, the cameras can be moved by the simulated forces, and the moving lights can influence the final simulation. 8 Physical Properties of Objects  Mass is the physical property of an object that most influences a dynamic simulation.  The mass of object can be easily determined based on its volume and density.  The volume of 3-D objects can be automatically calculated by most computer animation programs.  So the density of an object is often the only value that animators are required to provide in order for the software to calculate the mass of the object. 9 Physical Properties of Objects  Other characteristics of the object can also contribute to the realism of its motion.  Elasticity and stiffness can be used to define the rigidity or flexibility of an object especially at the times of collisions (Fig 12.3.3)  Rigid objects do not bounce far from a collision, and their surfaces do not move much e.g. a steel ball  Flexible objects may bounce far away from the collision point. The surfaces of flexible objects also deform significantly as a result of the collision and may keep moving moments after the collision took place e.g. a solid ball made of hard rubber, a sphere made out of gelatin. 10 Types of Forces  Many types of forces can be simulated with motion dynamics techniques.  The basic forces include linear forces, point forces, and conical forces.  These basic forces can be used in combination with one another to create more complex forces.  A linear force is unidirectional; it has one intensity value, and is traditionally represented with a vector e.g. wind and gravity, punching, or throwing  A point force or radial force travels like rays in all directions e.g. bomb that explodes in all directions  A conical force resembles a collection of linear forces that spreads out of a single point resembling the shape of a cone. When these forces impact a surface, they are strongest at the center of the impact area and weaker at the edges e.g. fan 11 Types of Forces  Forces can be applied locally or globally.  Local forces affect only one object or one joint e.g. one ball pushing another ball on a billiard table  Global forces affect all the objects in the 3-D environment e.g. Earth’s gravity  Forces can also impact, attract, or resist objects.  Impacting forces push objects away from the source of the force e.g. wind  Attracting forces pull the objects in e.g. magnet  Resisting forces offer resistance or opposition to objects moving through the 3-D environment e.g. friction and viscosity that can slow motion down 12 Types of Forces  Friction happens when one surface rubs against another.  All spaces, unless they are a vacuum, have some amount of viscosity or environmental density that facilitates or impedes the motion of objects  E.g. in underwater scenes, moving objects encounter more resistance from the density of water than they do from the density of air 13 Collision and Collision Detection  The motion that results from a collision can be calculated in a variety of ways.  The simplest approach consists of aiming the collision forces at the center of the object, and assuming that the mass is distributed evenly throughout the object.  Other approaches can be used to simulate richer and more realistic motion, but they are also much more time-consuming to calculate.  Symmetric objects usually have a balanced distribution of mass, but irregular objects with an uneven distribution of mass such as meteorites tend to have unpredictable motion.  When forces are applied to objects on parts other than the center of gravity they tend to produce motion that is not linear.  These forces are call torques because the motion they produce is in the form of rotations or torsions with varying amounts of rotational velocity and acceleration, and changing orientations (Fig 12.3.8) 14 Facial Animation  The facial animation of a character ends up being a big part of what audiences see on the screen.  When blocking out the animation of a face, it is useful to start by animating the eyes because audiences usually look at the eyes first.  It is also important to keep different timings for each of the different major components of a face, such as the eyebrows, lips, and nose  Controlling the jiggle of skin motion is also an effective way to convey secondary motion and a sense of mass.  When synching the lips to the dialogue, it is best to focus on animating the important intonations 15 3ds Max - Morph Target animation test 16 Morphing Targets and Phonemes  Using targets and morph interpolation to keyframe specific emotions and using phoneme shapes to do lip synch is a common way to do facial animation.  A library of key expressions is a simple and convenient way to store and retrieve many facial expressions.  Fig 12.5.2 and 12.5.4 show a set of simplified phonemes that can be used as morph targets.  Fig 12.5.3 and 12.5.5 illustrate libraries of lip key positions, facial expressions, and an interface that allows animators to place those keyframes in the animation while viewing a graphic representation of the soundtrack.  The motion transitions between facial expressions have to be checked for details in the interpolation that may look unnatural and, therefore, be distracting. 17 18 19 Animating Facial Expressions in 3ds Max - Part 2 - Morpher Modifier  https://youtu.be/MMHfDujrGwo 20 Facial Motion Capture  Facial motion capture data is usually obtained with a face tracker and markers on the face.  The number and placement of sensors and markers in a face tracker varies from system to system.  Special contact lenses can be placed on the eyes to capture eyeball motion.  It is common to combine motion capture data with other facial animation techniques because often the motion capture data is not sufficient to generate well-defined expressions.  Usually, additional animation detail is built on top of the motion capture data. 21 The model pictured in Fig 9.3.3 was captured with 80 markers and 45 control points in the Vicon system. 22