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7M836 Animation & Rendering

7M836 Animation & Rendering. Animation. Jakob Beetz J.Beetz@tue.nl. Joran Jessurun A.J.Jessurun@tue.nl. Week 8. Subject: Virtual Reality and Examples When: June 14 th Where: Design Systems Lab. (Vertigo 9.16). Animation. History of cartoon and computer animation

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7M836 Animation & Rendering

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  1. 7M836 Animation & Rendering Animation Jakob Beetz J.Beetz@tue.nl Joran Jessurun A.J.Jessurun@tue.nl

  2. Week 8 Subject: Virtual Reality and Examples When: June 14th Where: Design Systems Lab. (Vertigo 9.16)

  3. Animation • History of cartoon and computer animation • Extensive description of techniques and algorithms Rick ParentComputer Animation, Algorithms and Techniqueswww.cis.ohio-state.edu/~parent/book/outline.html • How to make an animation • Exampleswww.pixar.com

  4. Animation • Animation • “To give live to” • Make objects change over timeaccording to scripted actions • By showing a sequence of fastchanging images • Series images (frames) • Film 24 fps • Video 30 fps => 1 hour animation 108000 frames

  5. What can be animated? • Position and orientation of objects • Geometry (shape) and scaling of objects • Illumination • Reflection • Camera • In fact, everything!

  6. Animation process - traditional • Storyboard • The story • Sequence of images with descriptions • Key frames • Draw a number of important images (key frames) • Motion-based description • Inbetweens • Draw the rest of the frames • Painting • Redraw frames onto cels • Color them in • Put animation onto film

  7. Key framing Computer animation • Computer animation pipeline • 3D modeling • Motion specification • Motion simulation • Rendering • Post-processing

  8. Keyframe animation • Each “keyframe” specified by a number of key-parameters (state) • Inbetweening: Interpolate these parameters

  9. Keyframe animation • For each key parameter, specify value at “important” frames • Computer creates path for each parameter by interpolating this key parameter for inbetween frames

  10. Interpolation • Linear interpolation • Usually discontinuities • Not a smooth movement

  11. Interpolation • Spline interpolation • Smooth transitions • Beware of unwanted side effects

  12. Interpolation – speed control • Include velocity of interpolation • It is often more realistic to start a movement slowly, then speed up, and end it again slowly • Use speed curve • Speed curve relates time with position on interpolation spline • Position on interpolation spline determines interpolated key parameter value

  13. Interpolation – speed control

  14. Keyframing summarized • Specification of key frames/parameters • Determine key parameters and their values at certain important points in time • Specify type of interpolation • Specify speed curve for interpolation • Computer generates inbetween frames

  15. Animation of articulated structures • Articulated structure: • Object consists of a number of (sub-)objects (links) connected by joints • Each joint is specified by at least one (key-)parameter • Movement of object described by changing parameter values

  16. Constraints on joints Examples of joints

  17. Skeleton consists of 14 joints Each joint has 2 or 3 degrees of freedom Some parameters constrained Articulated structure

  18. Kinematics • Kinematics is the study of movement of (hierarchical) objects • Position, orientation, velocity, acceleration • Without taking into account dynamic properties (forces) (dynamics) • Forward kinematics • Inverse kinematics

  19. Forward kinematics • Animator sets parameter values for joints • Computer computes positions/orientations for links links:

  20. Forward kinematics • Animation by specification / interpolation of joint parameters

  21. Forward kinematics

  22. Forward kinematics

  23. Forward kinematics

  24. Kinematics • What to do when animation knows the desired end-position of the (sub-)object? • E.g. to grab something?

  25. Inverse kinematics • Animator specifies position (and orientation) within scene at wich link (end-effector) has to be positioned • Computer computes joint parameter values to get link at desired position: • After that. computer computes positions of all links by applying these joint parameter values for all joints

  26. Inverse kinematics

  27. Inverse kinematics • Animation by specification / interpolation of end-effector position • Or animation by interpolation of joint parameter values at start and end frame

  28. Inverse kinematics • Problems • Often more than one solution • Extra requirements to solution • Result not always desired path (e.g. collisions) • What to do when end-effector position specified outside operation area of object?

  29. Inverse kinematics • Inverse kinematics is also used to compute dependency of joint parameter values • E.g. for object with closed loops

  30. Kinematics summarized • Forward kinematics • Animator controls through joint parameters • Direct control over object state • Often many parameters to control • Inverse kinematics • Animator controls through position/orientation end-effector • Simpler specification of movements • Less parameters • Better feeling for positions in scene • Complex computations

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